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Integrating Multiscale Observations of U.S. Waters (2008)

Chapter: 4 Case Studies on Integrated Observatories for Hydrological and Related Sciences

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Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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4
Case Studies on Integrated Observatories for Hydrological and Related Sciences

Because the importance of hydrological observatories has been recognized for decades, many existing field study sites are available that illustrate how innovative sensor technologies and modeling approaches are being, or could be, applied. In this chapter, case studies drawn from the expertise of committee members and their many collaborators are presented. They represent a broad range of different types of projects in terms of motivation, location, design, and duration of study. Some primarily describe on-going activities while others represent proposed activities that would be overlain on existing but limited monitoring or science programs.

Each example is presented to highlight one or more important issues related to the design and operation of hydrologic observatories, test beds, and campaigns. However, this report is not recommending that these specific case studies be undertaken. Further, the individual case studies are intended only to illustrate the kinds of sensors, sensor networks, or data analysis that could be valuable in integrated observation systems, rather than to provide specific advice to any governmental entity. Generalized findings and conclusions derived, in part, from the case studies taken as a whole are found in Chapter 5.

INTRODUCTION TO THE CASE STUDIES

Monitoring the Hydrology of the Everglades in South Florida” provides an excellent example of a large, complex, integrated observatory designed for pressing water management needs in an ecologically sensitive area. This case study describes how the South Florida Water Management District (SFWMD) together with the U.S. Army Corps of Engineers and numerous other state, local,

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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and tribal partners are working together on issues of water quantity and quality, flood management, and ecosystem protection. The case study describes a large monitoring network of hydrological, meteorological, and other sensors along with the hardware and software infrastructure needed for data collection and management. Some new sensor systems that potentially could be employed to enhance ecosystem monitoring are identified. The case study illustrates the importance of interagency cooperation, which can be crucial to the success of complex observatories for hydrological and related sciences.

Impacts of Agriculture on Water Resources: Tradeoffs between Water Quantity and Quality in the Southern High Plains” addresses the impacts of agriculture on water resources, with a focus on semiarid regions where water availability is a critical issue and where cycling of salts has large-scale impacts on water quality. This type of study is particularly important given that world food needs will continue to increase, that many nations are turning to biofuels, and that climate change may worsen drought in many parts of the world. The case study discusses the types of measurement and monitoring programs that should be conducted to provide the necessary information to develop sustainable water and land resource management programs in the High Plains. In the High Plains, large time lags exist between forcing (land-use change) and response (increased recharge; change in water quality). Hence, the study provides a ‘classic’ example of why long-term observations often are critical, and why it is important that observatories have the capability to endure through changing budget cycles.

Hydrological Observations Networks for Multidisciplinary Analysis: Water and Malaria in Sub-Saharan Africa” extends the case study examples to include the Developing World and direct issues of world health and medicine. This study demonstrates the importance of establishing consistency in sampling locations for different parameters, in this case analysis of climate and hydrological conditions versus malaria outbreaks. Proper coordination of physical, chemical, biological, and medical data collection, at appropriate spatial and temporal extents, is a key to inferring the controls on malarial outbreaks or the best methods for preventing such outbreaks. This case study thus emphasizes the axiom that the nature of the research question or research hypothesis plays an important role in the design of the associated observation network.

Achieving Predictive Capabilities in Arctic Land-Surface Hydrology” explores a rudimentary strategy for robust remote sensing hydrology in the PanArctic, to identify capabilities needed to link in-situ observations to satellite sensor-scale observations. The assertion in this case study is that the appropriate mechanism for achieving this linkage is through robust models that span the scales of the hydrologic processes. Given the difficulty of access to Arctic sites and the sensitivity of the Arctic ecosystems, there is a pressing need for autonomous sensing stations at point- through plot-scales, airborne platforms for plot-through watershed scales, and satellite remote sensing for sub-watershed through Pan-Arctic scales. This case study therefore highlights the need for collecting

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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and integrating data at different scales and for developing novel methods for working in remote and challenging environments.

Integrating Hydroclimate Variability and Water Quality in the Neuse River (North Carolina, USA) Basin and Estuary” focuses on the impact of human activity and hydroclimate variability on watershed nitrogen sources, cycling and export, and their impacts on fresh water and estuarine ecosystem health. As outlined in this case study, the problem requires a synthesis of hydrologic, ecosystem and anthropogenic water, carbon, and nutrient processes within a coupled watershed and receiving estuary. Nutrient management in the Neuse watershed focuses on nitrogen, which is the limiting nutrient in the estuarine system. New sensing methods are emerging that promise to transform our ability to measure and understand nitrogen ecosystem dynamics. Hence, this case study demonstrates the need for integrating measurement of hydrologic, biogeochemical, and other ecosystem-related processes, and for building coordinated teams with interdisciplinary capabilities.

Mountain Hydrology in the Western United States” explains how snow in mountains of the West is the main source of the region’s water, with downstream hydrologic processes (e.g., groundwater recharge) and interactions with ecosystems controlled by processes at higher elevations. Hence, it is critical to develop models for water and energy fluxes in the western mountains that can take into consideration not only past and present conditions but likely changes brought about by climate change. The critical issue is the need for high spatiotemporal resolution due to sharp wet-dry seasonal transitions; complex topographic and landscape patterns; steep gradients in temperature and precipitation with elevation; and high interannual variability. Given the need for high spatiotemporal resolution data, this study illustrates the need for developing and taking advantage of emerging embedded sensor network technologies, coupled with already existing monitoring and modeling strategies.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

CASE STUDY I
—MONITORING THE HYDROLOGY OF THE EVERGLADES IN SOUTH FLORIDA

The Everglades

The Florida Everglades (Figure 4-1) is one of the world’s largest freshwater wetlands. It was once a free-flowing river of grass that provided clean water from Lake Okeechobee to Florida Bay. The marshes and swamps acted as natural filters that recharged underground aquifers in the South Florida region.

Historically the pre-channelized Everglades hydrologic balance was maintained through long, slow, continuous, gravity flow of water. Because of the diversion of water, channelization of transient rivers, and loss of elevation through oxidation of soils, pump stations are now required to move water from canals to marsh areas or from one canal segment to another or to return seepage water that would otherwise be lost from the greater Everglades. Over 50 such stations now exist, pumping volumes ranging from ~200 cfs to ~4800 cfs (Susan Sylvester, SFWMD, written commun., November 2006).

Accordingly, today the releases from Lake Okeechobee are controlled. During normal climatic conditions, Lake Okeechobee outflows are able to meet the large water needs to the south of the lake. However, when the climate remains abnormally dry for an extended period (for one or two seasons), inflows may diminish to very low levels during the same period that demands on the lake will peak. Consequently, lake stages may fall very quickly to extremely low levels. Conversely, when climatic conditions are wetter than normal, large volumes of water enter the lake, coinciding with periods when water demands to the south will be minimal. These events cause lake stages to rise very quickly and require large volumes of water to be discharged to the Water Conservation Areas (WCAs) or to the St. Lucie and Caloosahatchee estuaries. Abrupt changes in flow or very large releases through the estuaries are harmful to these ecosystems.

The WCAs are the primary source of supplemental water for the highly developed urban areas along the southeast coast of Florida, with the lake being the alternate source. The WCAs were built as large water-storage impoundments in the Everglades to provide both water supply and flood protection for the urban areas. In addition to the agricultural and municipal water consumptive needs, water releases from the lake are required to meet the needs of the Everglades and the numerous coastal ecosystems. The WCAs and the Everglades National Park (ENP) are known today as the remnant Everglades. Water held in and released from the WCAs effectively recharges the Biscayne aquifer in some areas.

Over the past half-century measures taken to satisfy agricultural and urban development goals have degraded the Everglades ecosystems. To restore and maintain the vitality of these ecosystems as well as to enhance the reliability and quantity and quality of water supplies, and provide flood protection, the U.S. Army Corps of Engineers (USACE), the South Florida Water Management District and numerous other federal, state, local, and tribal partners involved in water

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-1 Map of the Everglades region in South Florida. The South Florida Water Management District is responsible for managing the hydrology and ecology in this area. SOURCE: NRC (2006a). © International Mapping Associates.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

management in South Florida, have developed a plan called the Comprehensive Everglades Restoration Plan (CERP). To learn how to better manage the water, and to better understand the impact of various regimes of water-quantity flows, stages, volumes and qualities, and their durations and timing, timely, comprehensive, and accurate monitoring information is essential. Considerable sums of money have been spent in establishing an elaborate hydrologic, meteorological, and water-quality monitoring system throughout the Everglades. This is an excellent example of how an integrated hydrological observatory can provide essential data for managing water quality and quantity, flood control, and ecosystem protection.

The South Florida Water Management District

The South Florida Water Management District (SFWMD or the District) is the primary agency responsible for monitoring, managing, and protecting water resources in a 46,439 km (17,930 mi) region of South Florida. The District operates approximately 3000 km (1800 mi) of canals and more than 200 primary water control structures to serve a population of over 7 million people. The District’s annual budget exceeds $1 billion of which some $20 million (about 2 percent) is spent on hydrologic monitoring and associated data management activities. (This number would be larger if such activities in the area of water quality were included.)

The hydrologic monitoring network of the District is divided into five parts: (1) rainfall, (2) meteorological, (3) surface-water stage, (4) surface-water flow, and (5) groundwater. These networks are spatially distributed over the geographic areas of the District. For each network, the District maintains records on the history and evolution of the network; information on sensor(s)/instrument(s) used; number and location of instruments; frequency of data collection; time interval of the available data; optimization or design of the network conducted; and relevant references used.

The District has been gathering data about the region’s water and land resources for more than 40 years. Information about past and current weather, rainfall, and changes in vegetation or land use is essential for current and future planning, operations, research, and restoration initiatives. Real-time data, especially when combined with historic data, help the District make more informed water resources management decisions. Information about how natural and manmade systems are working (or not)—individually and interactively—is essential to short and long-term water resources management and restoration.

Data Collection and Management

Modern electronic hydrologic monitoring, data collection, and management

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

began at the District in 1974. This has allowed water managers to remotely monitor strategic flood gates and control hydrologic conditions. The backbone of this system today is a 24-station microwave infrastructure with two-way radio extensions. This recently modernized microwave communications infrastructure now supports voice radio relay, supervisory control and data acquisition (SCADA), telephone circuits/trunks, and computer network traffic. SCADA systems include hardware and software components that scan all remote data, log data and system events, send alarms when abnormal conditions occur, and issue operator commands to remote devices. The District’s SCADA and Hydro Data Management (SHDM) Department is responsible for data collection and management (Figure 4-2).

The District’s SCADA system transmits and receives information on water stages or levels, wind velocities, rainfall, water temperature, salinity levels, and other data. The system operates continuously and uses wireless communications to monitor and control water level, water control gate positions, and pumping activities. It provides an early warning of possible flood problems by observing water level and rainfall trends. This computerized data collection system comprises the cornerstone of the District’s data collection through a District-wide network of real-time and near-time data collection stations. The District also obtains and processes a variety of manual data logs.

Hydrologic data management includes processing the data collected, summarizing, deriving and analyzing, storing, and publishing. Processed data are archived into two different databases, namely, Data Collection/Validation PreProcessing (DCVP) and DBHYDRO. Instantaneous (breakpoint) data are stored in the DCVP database, while daily summary and 15-minute interval data are published in the DBHYDRO database. End users can retrieve data from either of these two databases. DBHYDRO data are accessible to users through the web browser. Internal users can also retrieve information from the DCVP archive using the web browser.

The District maintains a structured quality assurance/quality control procedure to ensure that data collected is of the best possible quality before it is further published. Pre-processing is the first stage of operations applied to “raw” time series data collected within the District’s monitoring network. Data records are collected and posted to DBHYDRO after data processing. Data quality assurance is normally performed during data processing. However, for some select legally mandated sites and for baseline data used in regional modeling and CERP, some post-processing quality assurance/quality control including graphical plotting and statistical analysis, are also performed.

Monitoring Networks

As of April 30, 2007, the District actively operates and maintains a network of 287 rain gauges to obtain rainfall data. These data are supplemented by radar

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-2 The hydrometeorological data flow and process. SOURCE: Pathak (2008).

rainfall NEXRAD (Next Generation Radar) data. The District also operates and maintains 45 active weather stations. In addition, data used to estimate daily potential evapotranspiration (PET) by “the Simple Method” several methods are available for 19 weather stations. A network of 1265 active surface-water stage gages provides surface-water stage data for various water bodies. Additionally, the District owns and operates a network of 446 active surface-water flow monitoring sites that provide instantaneous flow data at 15-minute intervals. From these data mean daily flows data are derived. The groundwater monitoring network has a total of 905 groundwater wells that are monitored on an interval basis of 15-minute, monthly, or greater than 1 month. The hydrologic monitoring network at the District is dynamic in nature and is constantly being expanded and optimized to the changing needs of the District.

Rainfall Measurements: The Importance of Employing Complementary Methods

An example of how different methods of data collection can complement one another is shown by the NEXRAD system. NEXRAD or Weather Surveillance Radar data provides complete spatial coverage of rainfall amounts unob-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

trusively using a predetermined grid resolution (usually 2 km × 2 km or 4 km × 4 km). The NEXRAD rainfall data is limited by reliance on the measurement of raindrop reflectivity, which can be affected by factors such as raindrop size and signal reflection by other objects. Because the reflected signal measured by the radar is proportional to the sum of the sixth power of the diameter of the raindrops in a given volume of atmosphere, small changes in the size of raindrops can have a dramatic effect on the radar’s estimate of the rainfall. For this reason, the radar is generally scaled to match volume measured at the rain gages. The best of both measurement techniques is realized by using rain gage data to adjust NEXRAD values.

Surface-Water Flow Monitoring Network: Linking Monitoring with Control

The District operates a network of 446 active flow monitoring sites that are used in operations, planning, and regulatory aspects of water management. The flow monitoring network is shown in Figure 4-3. The District works closely with the U.S. Geological Survey (USGS), USACE, and various local agencies in measuring and/or estimating flow throughout the District’s water control facilities. Water control structures are used to divert, restrict, stop, or otherwise manage the flow of water. These water control structures include pump stations, spillways, weirs, and culverts. District structures are typically designed to operate under a combination of water levels and operating regimes, which in turn result in varying flow conditions. Flow that moves through the structures are estimated by using a rating equation appropriate for the flow conditions based on the structure’s static and dynamic data. The “static” data include the geometric characteristics of the structure, whereas the “dynamic” data comprise the water stages (headwater and tail-water) and operating conditions (gate opening and pump speed).

Groundwater Monitoring Network: An Example of Interagency Cooperation

Groundwater monitoring data are needed to assess long-term trends in groundwater availability; to develop, verify, and calibrate groundwater flow models; to assess temporal groundwater conditions during droughts; to provide data for water-use permit application evaluations; to assist the District in legal proceedings involving regulatory and other groundwater disputes; and to use in designing and evaluating various District projects. The District groundwater network consists of wells that have data publicly available through the District’s DBHYDRO database but also in other databases not publicly accessible (these are mostly project specific). There are ongoing plans to migrate both of these databases into the DBHYDRO database. The groundwater network also con-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-3 District flow monitoring network. SOURCE: Reprinted, with permission, from Pathak (2008).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

sists of wells monitored by USGS through a cooperative agreement with the District. Most of the data on these wells are also available in DBHYDRO, but some can only be assessed from USGS’s Automated Data Processing Systems (ADAPS) database.

The District measures groundwater levels by using a pressure transducer, typically connected to a data logger. Thepressure transducers measure head pressure. The transducers communicate with the data loggers through an electronic cable. The data loggers then convert measured pressure values into water levels and record these data for subsequent downloads via laptop computers. Alternatively, data from some of the wells connected to the data loggers are sent via telemetry.

Ecological Monitoring: Merging Established and Emerging Approaches

The Everglades/Florida Bay landscape is a mosaic of different habitats that have evolved under a highly dynamic set of environmental conditions. As with any complex system, interactions among its different components are a fundamental aspect of its operation and play an important role in sustaining the Everglades. The physical hydrology, biogeochemical nutrient cycling, and biology of plant and animal communities are determinants of the emergent ecosystem properties that comprise the landscape. Monitoring these different “processes” that “drive” the system is providing data on how to best restore and maintain this dynamic landscape.

Monitoring the complex hydrologic, floral, and faunal changes associated with restoration activities is an enormous task. Many physical, chemical, and biological parameters have been identified as measures, or indicators, of overall performance of proposed restoration activities. Carefully designed and methodically implemented system-wide monitoring strategies are needed to successfully quantify both short- and long-term changes within the interdependent landforms, vegetation assemblages, and animal communities.

Due to the vastness (some 3 million acres) of the Greater Everglades, including the surrounding agricultural and urban environments, fixed monitoring stations (e.g., stage gages, water-quality collection sites), and vegetation/soil field sampling schemes (e.g., points, transects) cannot yield the high density of sampling data needed to adequately characterize and model the diverse ecosystems. Remotely sensed data, which is able to cover large areas with uniformly distributed high-density data points, has been and will continue to provide the essential synoptic view of restoration activities and their effects.

Work is underway to develop realistic and attainable strategies to expand the effective utilization of remotely sensed data for CERP system-wide adaptive monitoring and assessment. This involves the participation of biologists, chemists, hydrologists, and engineers in matching potential remote sensing technologies (sensors and analysis techniques) with the data required for effective water

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

and ecosystem management. These data include vegetation types and patterns over time and space, including invasive species, and measures of habitat change and suitability for selected ecosystem indicators ranging from the ubiquitous cyanobacteria periphyton to the Florida panther. These data also include water quality (e.g., nutrients and mercury), vegetation, and food webs that support wading birds and tree island communities, changes in topography, and the nesting and feeding activities of alligators and various species of wading birds.

The Florida Everglades are ripe for integration of embedded sensor networks for hydrological and ecosystem monitoring with the already existing monitoring systems. Embedded network ecosystem monitoring systems are currently being developed at the University of California James San Jacinto Mountains Reserve biological field station (http://www.jamesreserve.edu; Hamilton et al., 2007). In addition to the biogeochemical and meteorological embedded sensor systems described in Chapter 2, researchers at the James Reserve are equipping bird nest boxes with microclimate sensors and a downward-pointing, miniature, infrared, sensitive charged-coupled device (CCD) camera and a diffused, infrared light-emitting diode (LED) light source. The cameras deliver JPEG images at 10 frames per second, which are reviewed by a staff biologist to record nest box activity during the nesting season. Such approaches could be used in the Florida Everglades to help monitor the health of species and ecosystems.

Summary

The fate of the Everglades is a dramatic case study of a global issue: freshwater quantification and allocation. Monitored data obtained from the District’s databases provide water managers at any time with knowledge of the amounts of water available throughout the region. Based on this information, they make their flow allocation decisions that redistribute the water within the region each day.

Decisionmakers from around the world are watching South Florida, to see how wetland restoration will be balanced against economic development and societal demands. Scientists are currently developing interim goals and a strong monitoring and assessment plan for the Everglades. These efforts will supply the data needed to reduce the ecological and economic risks associated with adaptive restoration, and hopefully provide the framework for the successful restoration of this national treasure.

The Everglades serve as an example of several important axioms related to integrated observations of hydrologic and related sciences. First, integrated observatories can play an essential role for such critical activities as water management, flood control, and ecosystem monitoring. Second, observations in such politically, economically, and ecologically sensitive systems as the Everglades need to be done with great care, combining relatively simple and sophisticated and often expensive approaches. Finally, observational networks provide data, on which understanding can be built; however, understanding complex systems takes time.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

Hence, as shown in the Everglades, there needs to be a long-term commitment to hydrological and ecosystem monitoring, with development and integration of new and emerging methods.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

CASE STUDY II
—IMPACTS OF AGRICULTURE ON WATER RESOURCES: TRADEOFFS BETWEEN WATER QUANTITY AND WATER QUALITY IN THE SOUTHERN HIGH PLAINS

Problem Statement and Importance

Agriculture has large-scale impacts on water resources. This case study focuses on semiarid regions where water availability is a critical issue and where cycling of salts has greatly affected water quality. Large reservoirs of salts (e.g., chloride, sulfate, and nitrate) have built up in soils as a result of evapotranspirative enrichment of atmospherically derived salts under natural ecosystems over millennia in many semiarid regions, such as Australia, the southwestern United States, and Africa (Figure 4-4) (Allison et al., 1990; Edmunds and Gaye, 1997; Phillips, 1994; Scanlon et al., 2007). This system is generally not dynamic and responds slowly to land-use and climate change. Changes in the water cycle related to land-use change can increase recharge and mobilize salt reservoirs, degrading groundwater and surface-water quality.

Conversion of natural ecosystems (grasslands or forests) to rain-fed agriculture often increases water resources through enhanced recharge (Figure 4-4). The classic example of increased water resources caused by cultivation is provided by conversion of forests to crops in Australia, which increased recharge up to two orders of magnitude, raising groundwater levels and baseflow to streams (Allison et al., 1990). In contrast, irrigated agriculture decreases water resources through elevated water use (Figure 4-4). Irrigated agriculture accounts for about 80 percent of global water withdrawal and about 90 percent of global water consumption (Shiklomanov, 2000). Irrigation is also one of the primary users of water in the United States and currently accounts for about 64 percent of freshwater withdrawal (excluding thermoelectric use) (Hutson et al., 2004). The water balance changes associated with irrigated agriculture cause changes in water quality. Increased recharge is generally associated with degradation of the quality of groundwater and surface water resulting from mobilization of salts in semiarid vadose zones and application of fertilizers in arid and humid settings (Figure 4-4). Reduced water quantity related to irrigation is generally associated with degradation of water quality also as a result of soil salinization and nutrient contamination from fertilizers.

In the future agriculture will come under increasing stress to meet the food requirements of projected increases in human population from 6 billion (2000) to 9 billion (2050). Many different approaches are being proposed for increasing food production, including expansion of rain-fed agriculture into nonagricultural areas (forests, grasslands), expansion of irrigated agriculture, increased use of fertilizers, and limited irrigation through rainwater harvesting in rain-fed areas. Development of sustainable agriculture in newly converted agricultural areas and remediation of water-quality and -quantity problems in existing agri-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-4 Schematic of different land-use settings: natural ecosystems including (a) forest and (b) grassland, agricultural ecosystems including (c) rain-fed and (d) irrigated agriculture. There is little or no recharge beneath natural ecosystems in semiarid and arid regions and salt and nutrient reservoirs are found in the unsaturated zone. Conversion of natural ecosystems to rain-fed agriculture results in decreased evapotranspiration and increased runoff (not shown) or recharge (W, water), raising water tables and mobilizing salts (S) in semiarid regions and nutrients from fertilizers (F) in semiarid or humid regions. Salts are derived from precipitation and fertilizers and nitrate from precipitation, N fixing vegetation (V), and fertilizers (F). Irrigated agriculture has an additional input of irrigation water that can be derived from surface water or groundwater. Irrigated agriculture generally results in increased recharge from irrigation return flow (I). Salts are mobilized by increased drainage in semiarid regions in groundwater-fed systems. SOURCE: Modified, with permission, from Scanlon et al. (2007). © 2007 American Geophysical Union.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

cultural areas require a thorough understanding of how agriculture impacts water resources and land quality. Types of questions that need to be addressed include

  1. How does rain-fed agriculture increase groundwater recharge?

  2. How can water-quality problems caused by increased recharge and flushing of salts related to agriculture be remediated without greatly reducing water quantity?

  3. Can natural ecosystems be converted to agriculture in the future with minimal impacts on water quality?

  4. What impact do government programs that remove land from cultivation have on water resources?

  5. What impact does conversion of agriculture to natural ecosystems (forests, grasslands) have on water resources (water quantity or quality)?

  6. Can irrigation be managed to minimize negative impacts on water resources?

  7. Can impacts of land-use change be reversed by simply reversing the land use?

  8. What time lags are associated with forcing (land-use change) and response (impact on water or land resources)?

Many water resources problems related to agriculture are being addressed in different programs. Australia is trying to develop schemes to reverse dryland salinity problems caused by cultivation through crop management programs (reduced fallow periods, perennial versus annual crops) and afforestation without greatly reducing water quantity. In developing countries, rain-fed agriculture is projected to expand by 13 percent by 2030 to meet increased food demands of a growing population (Bruinsma, 2003). It will be important to manage such landuse changes to minimally impact water resources and land quality. In many areas, cultivated lands are being converted to natural ecosystems through unmanaged land abandonment, afforestation for timber production or carbon sequestration, and government policies such as the Conservation Reserve Program in the United States; however, the impacts of many of these land-use changes on water resources are generally not evaluated. Irrigated agriculture is projected to increase by 20 percent by 2030, further stressing scarce water resources (Bruinsma, 2003). There is increased interest in reducing water use associated with irrigated agriculture; however, extremely water-efficient irrigation systems can result in soil salinization because salts built up in the soils are not flushed through the system. The challenge will be to develop irrigated agricultural programs that are sustainable without negatively impacting land and water quality. Rotations of irrigated and rain-fed agriculture or minimal irrigation of rain-fed agriculture with rainwater (rainwater harvesting) may provide solutions to this problem (Rockstrom and Falkenmark, 2000).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

The Southern High Plains

The southern High Plains provide an excellent case study for the problem of assessing impacts of agriculture on water resources (Figure 4-5). The basic issue addressed in this case study is which measurement and monitoring programs would need to be conducted to provide the necessary information to develop sustainable water and land resource management programs.

The High Plains (450,000 km2 area), extending from South Dakota to Texas, are one of the most important agricultural areas in the United States. They represent 27 percent of the irrigated land and 20 percent of the groundwater used for irrigation in the United States (Dennehy, 2000; Qi et al., 2002). The southern High Plains (75,470 km2) in Texas include 11 percent irrigated agriculture, 44 percent dryland or rain-fed agriculture, 32 percent grassland, and 12 percent shrubland (Scanlon et al., 2005). Although the percentage of land use represented by irrigated agriculture in the southern High Plains is low, irrigation accounts for about 94 percent of groundwater use and has resulted in groundwater-level declines (average 43 m over 10,000 km2 over approximately 55 yr) from pre-development levels (Figure 4-6) (Qi et al., 2002; Fahlquist, 2003; McGuire, 2004). The southern High Plains are extremely flat, and most of the surface water drains internally to approximately 16,000 endorheic ponds or playas (Figure 4-5). Recharge is focused beneath playas; regional rates are about 11 mm/yr (Figure 4-7) (Wood and Sanford, 1995). There has been no recharge for the past 10,000 to 15,000 yr (since the Pleistocene) in natural ecosystem settings (grasslands and shrublands) in interplaya regions (Figure 4-7) (Scanlon and Goldsmith, 1997). Conversion of natural ecosystems to rain-fed, cultivated crops has increased recharge to about 25 mm/yr over a 3200-km2 area (median value; about 5 percent of mean annual precipitation). Irrigated agriculture is fed entirely by groundwater and has resulted in groundwater depletion. The fate of drainage water or irrigation return flow is not known for most areas; however, studies by McMahon et al. (2006) indicate that irrigation return flow is still within the unsaturated zone and has not reached the water table. Groundwater quality is degrading, as shown by 31 to 221 percent increases in total dissolved solids and nitrate beneath cultivated areas (Scanlon et al., 2005).

Potential land-use and water-use scenarios that may be considered to maintain or increase food production and improve water resources include

  1. Enhancing productivity of rain-fed agriculture,

  2. Expanding agriculture into natural ecosystems (grasslands and shrublands), and

  3. Increasing water- and nutrient-use efficiency of irrigated agriculture.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-5 Groundwater-level changes caused in the southern High Plains, declines resulting from irrigation and increases resulting from conversion of rangeland to dryland agriculture. The area of greatest declines in the northeast region has an average value of 43 m (average pre-development time of 1945 to 2003). SOURCE: Modified, with permission, from Scanlon et al. (2005). © 2005 by Blackwell Publishing.

FIGURE 4-6 Typical view of a playa in the High Plains in Texas. There are approximately 30,000 playas in the southern High Plains that cover ~2 percent of the surface area. SOURCE: Photo courtesy of High Plains Underground Water Conservation District No. 1, Lubbock, Texas.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-7 Schematic of water cycle in the southern High Plains, emphasizing focused recharge beneath playas and no recharge (evapotranspiration) in interplaya settings under natural ecosystems. Pressure heads close to 0 and low chloride concentrations in soil water beneath playas result from focused recharge. Upward pressure head gradients and bulge-shaped chloride accumulations beneath natural ecosystems in interplaya settings result from no recharge during the past ~10,000 yr since the Pleistocene glaciation. SOURCE: Based on data from Scanlon and Goldsmith (1997). © 1997 by American Geophysical Union.

Methods of enhancing food productivity of rain-fed agriculture include limited irrigation with rain (rainwater harvesting) over short dry periods, reduced fallow periods, terracing, even cropping to reduce bare soil evaporation and increase water use by crops (transpiration), and reduced drainage beneath crops (Scanlon et al., 2007). A large part of the southern High Plains (44 percent) is uncultivated. Can rain-fed agriculture expand into this region without negatively impacting water resources? Approaches to increasing water- and nutrient-use efficiency in irrigated areas include various irrigation systems, such as subsurface drip to reduce evaporation of irrigated water, precision agriculture using global positioning systems to collocate water and fertilizer applications with crop roots, various tillage approaches (no till, minimum tillage) to reduce runoff and increase infiltration, and perennial cropping to sequester nitrate and reduce groundwater contamination.

Current research in the southern High Plains is focusing on subsurface drip irrigation and water-quantity issues, with little emphasis on potential for soil and water salinization. Salinization may take decades to develop, and this issue may be more readily assessed using modeling analyses to determine the potential for

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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salinization. Soil profiling at 5-year time intervals to measure water, salt, and nutrient balances and electrical conductivity changes over time associated with different types of irrigation systems would also be useful in tracking the development of salinization. Remote sensing of vegetation parameters, such as leaf area index, over long time periods may also be used to evaluate early development of salinization associated with deficit irrigation. Baseline data can be collected in areas with center pivot or other types of irrigation systems. Overall, such measurements and modeling analyses will be essential to assessing sustainability of different agricultural programs with respect to land and water resources.

Information Needs

Fundamental information on various fluxes and stores in the water, salt, and nutrient cycles would be required to understand potential impacts of different land-use changes related to agriculture. It is critical to consider linkages and feedbacks among these various cycles within the context of water and land resources. Fluxes include precipitation, irrigation application, salinity and nutrient application, evapotranspiration (ET), runoff, groundwater recharge, and groundwater pumpage. Storages that would need to be quantified include surface-water storage (ephemeral lakes or playas), soil moisture storage, groundwater storage, and salinity and nutrient storages in surface, unsaturated zone, and groundwater. At a minimum, information on these fluxes and stores would be required at seasonal timescales that can be scaled up to annual timescales. In addition, crop phenology (leaf area index, root growth) would need to be quantified.

Existing Capabilities

A network of precipitation gages monitors hourly and/or daily precipitation in the southern High Plains. Information on chloride, sulfate, and nitrate in precipitation is being collected annually as part of the National Atmospheric Deposition Program (two stations in southern High Plains, 1994-2004; http://nadp.sws.uiuc.edu). Information on nutrient application rates at the county level is based on county fertilizer sales data and is available from the National Agricultural Statistics Service (http://www.usda.gov/nass/). Solar radiation, required for estimating PET, was available from meteorological stations in Lubbock and Midland from 1961 to 1990; however, these stations were discontinued. A new PET network was established that includes weather stations with solar radiation for PET estimation (Texas South Plains ET network). Estimation of reference crop ET from potential ET requires information on crop coefficients. Crop coefficients are currently being quantified using weighing lysimeters at the U.S. Department of Agriculture (USDA) laboratory in Bushland in the central High

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Plains (e.g., Howell et al., 2004). There is currently no monitoring of runoff to the 16,000 playas or variations in water levels in playas. Groundwater recharge has been estimated regionally using the chloride mass balance approach with groundwater chloride data (Wood and Sanford, 1995). Most of the recharge in natural rangeland settings is focused beneath playas. In addition, specific studies have been conducted at several sites throughout the southern High Plains to estimate recharge rates (Wood et al., 1997; Scanlon et al., 2005; McMahon et al., 2006). Regional recharge estimates have been provided by groundwater chloride data (Wood et al., 1997). Recharge beneath playas has been estimated using environmental tracers such as chloride and tritium (Wood and Sanford, 1995; Scanlon and Goldsmith, 1997). Recharge beneath rain-fed and irrigated agriculture has been estimated at about 10 sites using environmental tracers in the unsaturated zone and groundwater-level fluctuations in the saturated zone (Scanlon et al., 2005; McMahon et al., 2006). Groundwater levels have generally been measured once every 5 yr in the southern High Plains since the early 1900s, and data are available on the Texas Water Development Board (TWDB) website (http://www.twdb.state.tx.us). There is very little information on groundwater pumpage. Recently a program was implemented to install meters in irrigation wells to begin to characterize this flux.

There is little information on surface-water storage. Water levels in playas are not being monitored. Limited monitoring of soil moisture is being conducted at a few sites in natural ecosystems and irrigated sites (Scanlon et al., 2005). This system was installed as part of the USGS National Water Quality Assessment Program in the High Plains. Soil moisture is monitored annually by USDA prior to crop planting using a neutron probe. Groundwater storage can be estimated from annual groundwater level measurements conducted by the TWDB and is available on-line. Salinity and nutrient storage information is not available for surface water. Limited information on salinity and nutrient storages are available for the vadose zone in natural ecosystems and rain-fed and irrigated sites funded by USGS National Water-Quality Assessment (NAWQA) Program and Bureau of Reclamation (Scanlon et al., 2005; McMahon et al., 2006). This information is extremely valuable for quantifying potential loading of salts and nutrients from the vadose zone to groundwater caused by increased recharge related to cultivation. Long-term records on groundwater concentrations of major and minor elements are available for the past 40 to 60 yr on-line at the TWDB website. This excellent database of very high quality, which is provided by the state, is not available in most states within the United States.

A detailed groundwater model has been developed for the southern High Plains. All the data used to develop the model are available on-line at the TWDB database (http://wiid.twdb.state.tx.us).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Information Gaps

There are various gaps in our measurement and monitoring system of the water, salt, and nutrient cycles that need to be addressed. Many of the questions related to agriculture posed earlier can be evaluated using baseline measurements of environmental tracers, salts, and nutrients in the unsaturated zone. Before natural ecosystems are converted to agriculture, it is important to characterize the stores of salts and nutrients in the vadose zone because increased recharge related to cultivation can mobilize these salts and contaminate underlying aquifers, as seen in Australia (Allison et al., 1990). The issue is more critical for nitrate contamination relative to contamination with sodium chloride salts because of the lower maximum contaminant level (MCL) for nitrate-N (10 mg/L) relative to total dissolved solids (TDS) or chloride (500 mg/L TDS, secondary MCL for Cl, 250 mg/L).

Time series in groundwater quality over decades beneath agricultural areas would be required to assess impacts of agriculture on groundwater quality. The time lag between conversion to agriculture and increased groundwater recharge can also be evaluated using chloride profiles in the unsaturated zone in agricultural areas. Velocity of the solute front movement related to cultivation can be estimated beneath rain-fed agriculture and projected in order to estimate the time that the increased flux reaches the water table. Time lags are commonly long (decades to centuries). Therefore, negative impacts of land-use change may not be immediately apparent. In addition, attempts to reverse negative impacts of land-use change, such as dryland salinity in Australia, will also require long time periods.

A combination of unsaturated zone and groundwater data for nitrate can be used to determine whether fertilizers are being leached beneath cultivated areas. However, most measurements related to agriculture are restricted to the root zone, and rarely are profiles measured below the root zone or to the depth of the aquifer to assess leaching of nutrients. Chloride profiles can also be measured beneath irrigated agriculture to determine whether deficit irrigation, as is practiced in the southern High Plains, results in soil salinization. Preliminary results from limited profiles in the southern High Plains indicate that soil salinization is an issue because chloride concentrations in irrigation water are relatively high (≥500 mg/L TDS) and recharge from precipitation is insufficient to prevent this buildup of salts. These data suggest that current trends toward more efficient irrigation systems (e.g., ≤95 percent efficient) will increase salinity of the applied water by a factor ≤20. By focusing on water quantity alone, these programs are ignoring impacts on land resources.

Large time lags between forcing (land-use change) and response (increased recharge) often result in limited use of monitoring to address many of these issues. However, monitoring can provide process understanding related to impacts of cultivation on water and nutrient cycles. Monitoring ET over different land uses, such as natural ecosystems and rain-fed agriculture, can be used to

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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determine whether reduced ET associated with winter fallow periods in agricultural areas can account for increased recharge beneath rain-fed agriculture. If ET monitoring proves that fallow periods lead to increased recharge, then programs to reduce fallow periods to increase food production would reduce groundwater recharge. Impacts of reversing land-use changes to remediate water-quality problems associated with cultivation or abandoning agricultural areas can also be examined using ET data.

The current system of using potential ET and crop coefficients is based on limited spatial distribution of meteorological stations and crop coefficient data. This information could be greatly enhanced by using optical satellite-based data (Landsat Thematic Mapper [TM], Moderate Resolution Imaging Spectroradiometer [MODIS]) in programs such as Surface Energy Balance Algorithm for Land (SEBAL) and Disaggregated Atmosphere-Land Exchange Inverse Model (DisAlexi) to estimate regional ET (Bastiaanssen et al., 1998a, b; Anderson et al., 2004). One of the main problems with the satellite data is that the thermal band on Landsat TM is no longer functioning, and if the National Aeronautics and Space Administration (NASA) does not reinstitute a high-resolution thermal imaging system on future Landsat platforms for regional ET estimation this problem will continue indefinitely. The spatial scales of the Landsat TM (30 m) are appropriate for estimating ET at the field scale; however, data are available only once every 17 days. In contrast, the resolution of temperature data from MODIS is much coarser (250 m), although the temporal resolution is twice daily. Both Landsat and MODIS data can be used together to offset differing spatial and temporal resolutions.

Recently developed Large Aperture Scintillometer (LAS) systems can be used to provide information on sensible heat flux at scales up to 1 km. The relatively large scale of these LAS measurements makes these data suitable for ground-referencing sensible heat-flux estimates from satellite-based approaches. In addition, LAS systems can be used to estimate ET by monitoring other components of the energy balance equation (net radiation and soil heat flux). ET can also be estimated using GRACE (Gravity Recovery and Climate Experiment) satellite data (Rodell et al., 2004), using a water balance approach. The large footprint of GRACE data indicates that reasonable estimates of ET may be possible only for the entire High Plains system because of coarse spatial resolution. The proposed GRACE follow-on mission would likely improve the spatial resolution considerably.

Although monitoring of surface runoff is generally routine, very little information is available on spatial and temporal variability in storage in endorheic ponds or playas. Satellite data can be used to monitor variations in the surface area (Smith et al., 2005) and water depth (Alsdorf and Lettenmaier, 2003) of these playas; however, ground-based information on water levels and topography of playa floors would be required to translate area or depth information to storage volumes. Recent reductions in irrigation over the past two decades and projected future reductions in irrigation may result in reduced irrigation return

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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flow to playas, which would negatively impact these habitats for migrating birds. Monitoring playa water storage is also very important for recharge estimation because playas are the focal points of recharge (Scanlon and Goldsmith, 1997). Although many studies document impacts of climate variability on surface runoff, studies examining impacts of climate variability on endorheic water storage are limited.

Estimates of groundwater recharge are needed for all the different land-use settings in the region, which can be partly addressed through unsaturated zone profiles using environmental tracers such as chloride (Scanlon et al., 2005; McMahon et al., 2006). Soil physics monitoring can also be used to determine flow directions (upward or downward). If these recharge estimates can be linked to surface parameters such as vegetation or leaf area index, there is a potential to use satellite-based vegetation indicators to estimate spatial variability in recharge.

Groundwater storage is currently being estimated from annual groundwater-level monitoring data. GRACE satellites can also provide estimates of monthly, seasonal, and annual changes in groundwater storage over the entire High Plains (Rodell et al., 2002, 2006; Strassberg et al., 2007), as well as for smaller, regional aquifer systems (Yeh et al., 2006). Recent post-processing studies indicate that GRACE is capable of providing reliable information on water storage variations as much higher resolution (~150,000 km2) than was previously thought possible (Swenson et al., 2006). However, monitoring of groundwater levels should be increased to seasonal or monthly timescales to provide ground validation of the GRACE output. A recently developed commercial field superconducting gravimeter can also be used to estimate changes in subsurface water storage (precision <0.1 microgal, equivalent to water-layer thickness of 24 mm) over spatial scales similar to water-table depths (Peter et al., 1995; Goodkind, 1999). Survey gravimeters can be used to extend results from the point gravimeter to larger spatial scales.

Modeling analyses can be used to integrate measurement and monitoring data from different space and timescales, isolate controls on flow and transport processes, and conduct sensitivity analyses with respect to proposed future landuse changes and potential impacts on water and nutrient cycles. Because of generally long time lags associated with impacts and responses related to initial land-use changes or remediation schemes in these semiarid regions, it is essential to use modeling to assess different proposed management strategies. A variety of codes are available to simulate appropriate processes in this type of system, including land atmosphere, regional water balance, unsaturated zone, and groundwater codes.

Measuring and monitoring various components of the water cycle, such as precipitation, ET, runoff, and groundwater recharge, associated with different land-use practices can be used to provide information to water resources managers on linkages between land-use and water resources, including both water-quantity and water-quality issues. A comprehensive evaluation of total system performance that includes land use and degradation, water quantity, and water

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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quality is essential for considering trade-offs between water-quantity and water-quality impacts of different land-use changes, as well as land degradation associated with salinization. Although traditional approaches focus on single agricultural programs such as rain-fed agriculture or irrigated agriculture, combining or rotating these approaches may help to minimize negative environmental impacts. Rotating rain-fed agriculture with irrigated agriculture may help minimize salt buildup beneath deficit irrigated areas. Limited irrigation of rain-fed agriculture is being proposed in sub-Saharan Africa to increase food productivity of rain-fed systems and may be appropriate in the southern High Plains also. Modeling analyses can be used to evaluate more complex rotations. Results of the measurement, monitoring, and modeling analysis in the southern High Plains may be applicable to many water-scarce, semiarid regions facing similar problems of increasing food production with more limited water supplies, such as in Australia, Africa, India, and China.

Summary

The High Plains case study emphasizes the importance of linking land-use and water resources management and also the tradeoffs between water-quantity and water-quality impacts of land-use changes. Long time lags between land-use changes and water resource impacts, such as changes in recharge and salinization, place increased emphasis on use of environmental tracers such as chloride that archive impacts of land-use changes on groundwater recharge and salinity. Monitoring programs that quantify the various components of the water cycle and integrate ground-based and satellite information on precipitation, ET, runoff, and groundwater storage, can provide process information to assess controls on land-use change impacts on water resources. Sustainable water resources management in semiarid regions, such as the southern High Plains, will require an in-depth understanding of land-use change impacts on water resources and will likely require a shift from irrigation to rain-fed agriculture in many areas.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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CASE STUDY III
—HYDROLOGICAL OBSERVATIONS NETWORKS FOR MULTIDISCIPLINARY ANALYSIS: WATER AND MALARIA IN SUB-SAHARAN AFRICA

Malaria: A Global Health Problem

The nature of the research question or research hypothesis should play an important role in the design of the associated hydrological observation network. If the research question requires integration of knowledge and data from several disciplines, then it is necessary to design a network of observations that includes a suitable set of sensors or sensor systems, not necessarily limited to the traditional set of sensors used in hydrologic research. The observations network should be designed to sufficiently characterize the relevant physical, biological, and/or chemical processes at the appropriate spatial and temporal resolutions, and with sufficient precision and accuracy to be able to make useful decisions. In this section, a case study on the challenges of monitoring the interactions between the hydrology and the ecology of malaria in Africa is presented.

This is only one example of a broad set of water-related diseases. In the United States, mosquito-borne disease transmission (e.g., West Nile virus) is an important public health issue. Addressing these important research problems requires integration of concepts and tools from climatology, hydrology, entomology, and medicine. The approach used here is an example of landscape epidemiology, which involves identifying areas where a disease is present and/or transmitted. Key environmental factors such as temperature, precipitation, elevation, vegetation, and water levels, are combined with human factors such as population centers, land use, and transportation networks, and with characteristics of the disease itself (range, mode of transmission, etc.). Numerous examples of this approach are given at http://geo.arc.nasa.gov/sge/health/landepi.html.

Malaria profoundly affects people around the world, killing 3 million out of 300-500 million infected each year. The majority of the victims are children under the age of five (Persidis, 2000). This alarming rate has waned in the past as anti-malarial drugs became available but is now in a period of rapid resurgence in sub-Saharan Africa. It is estimated that in 1995, 200 million Africans were infected with malaria, and of these 1 million died (Snow et al., 1999). This recent trend has been widely reported (Hay et al., 2002), and as a result the disease has once again become a priority. Classic malaria drugs such as quinine and chloroquine have become substantially less effective as pathogens have developed immunity to them (Persidis, 2000), a factor that is likely to be partly responsible for the rising malaria death rates. Much of the ongoing research seeks to develop new drugs, vaccines, and other prevention strategies.

The societal concerns about malaria are not limited to conditions under the current climate. The International Panel on Climate Change (IPCC) concluded that malaria will likely be on the rise as a result of climate change. However, investigators disagree about the extent of the effect of climate change on the rate

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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and geographical extent of malaria incidence (Hay et al., 2002). Previous attempts to link the two processes have focused on statistical analysis of climate variables and malaria data at nearby locations. These attempts lack consistency in the spatiotemporal resolution and locations of the two different types of data, which are derived from observations networks in hydrology and human health that were designed independent of each other. In order to address this limitation, an observations network has to be designed in a consistent fashion to sample all relevant variables. The distribution of vectors for the mosquitoes carrying the disease depends on local climatic factors, and the occurrence of outbreaks and outbreak intensity are likely to depend on local weather and hydrology (Epstein et al., 1998). These connections are evident in Figure 4-8 from Niger, which illustrates clearly how reported incidence of malaria peaks following the rainy season.

Towards Better Understanding of the Connections between Water and Disease

A group of scientists from the Massachusetts Institute of Technology’s School of Engineering, the Harvard School of Public Health, the National Oceanographic and Atmospheric administration, and the Pasteur Institute has recently initiated a multidisciplinary research project that brings together their complementary expertise to address the complex interactions that lead to malaria transmission. This project is motivated by the following set of research questions:

  1. What is the role of local environmental conditions and microclimatic niches in dictating the local dynamics of individual mosquitoes and mosquito populations (dynamics being defined as mean level of abundance and rates of biting and survival)? What physical and biological processes dominate the complex interactions that take place between mosquito populations, human populations, and the environment?

  2. What are the relative roles of natural and man-made surface-water bodies in providing suitable habitat for sub-adult mosquitoes?

  3. Can the response of mosquito populations to seasonal and interannual climate variability in Africa be predicted?

The aim of this project is to develop an integrated computational model that is capable of simulating the spatial and temporal dynamics of malaria transmission in sub-Saharan Africa. Such a model is likely to provide a new tool for prediction of malaria outbreaks and in the screening of different strategies for combating malaria transmission, and will provide fundamental data on climate associations with malarial outbreaks that will enable assessment of the impact of climate change on malaria transmission and its regional extent. A detailed nu-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-8 Weekly malaria cases in Niger from 2001 to 2003 and precipitation data (average monsoon conditions).

merical representation of all the physical and biological processes that govern the rate and extent of malaria transmission is included. The researchers envision a numerical simulator that will explicitly describe, at fine spatial and temporal resolutions (~10 m, 10 minutes), the interactions between the natural environment and the populations of mosquitoes, parasites, and humans. Such a tool will provide a suitable framework for integration of hydrological and entomological observations with other information about soil type, vegetation cover, and topography.

The three main objectives of the project are

  1. To build consistent data sets on climatic conditions, hydrologic conditions, mosquito populations, and malaria incidence; these data sets are needed for characterization of processes, calibration of model parameters, and verification of model performance;

  2. To develop a discrete model of mosquito population dynamics incorporating variables affecting the development rate, pupal productivity, and adult longevity of Anopheles gambiae s.l. mosquitoes; and

  3. To couple this mosquito population model to a detailed, fine-scale, hydrologic model that describes the natural environment for mosquito population including seasonality, distribution, and persistence of suitable larval habitats.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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In order to achieve objective 1, the foundation for the other objectives, a network was designed to collect observations of rainfall, incident solar radiation, air temperature, humidity, wind speed and direction, soil saturation, microtopography, levels in water pools, spatial extent of pools, groundwater level, mosquito density, larva count, and malaria incidence (see Figure 4-9).

The design of this network integrates sensors that are traditionally used in hydrology for monitoring rainfall rate and soil moisture level, and in entomology for monitoring mosquito density and larva count, as well as standard meteorological sensors of temperature, humidity, and wind. The monitoring of the micrometeorology and soil hydrology is automated, and these observations are recorded by data loggers at about hourly resolutions. The weekly monitoring of the larva prevalence is done by dipping small containers into the water body of interest followed by visual identification, and counting. The monitoring of adult mosquito density is carried using standard U.S. Centers for Disease Control (CDC) light traps followed by laboratory identification of the mosquito species, and counting. There are needs for development of new automated sensors for monitoring the mosquito population at the adult and larva stages. Automatic cameras can be deployed to monitor the larva prevalence in water bodies. New sensors that respond to the movement and associated sound of adult mosquito may provide information about their density.

FIGURE 4-9 Deployed sensors in villages of Banizombou and Zindaru, near Niamey in Niger. CDC - U.S. Centers for Disease Control, RH - is relative humidity.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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The density of the sensors in Figure 4-9 characterizes the spatial resolutions resolved by the network. The resources needed for the labor-intensive processes of field counting of larva and laboratory identification of adult mosquito species are the main limiting factors for expanding the density of the deployed sensors. Extrapolation of these observations from the village scale to the regional scale would require the use of remote sensing technology, from satellites and other airborne platforms, in order to study the same processes at the regional scale. The new generation of active microwave sensors (such as those deployed in RADARSAT2) will offer a great potential for monitoring of water bodies that are likely to provide the breeding sites for mosquito. These sensors will enable monitoring of these water bodies at a resolution of a few meters.

A New Role for Remote Sensing Observations in Global Health Research

Because ground observations of surface-water prevalence are time consuming and difficult to carry out over large areas, an attractive alternative has been to use remote sensing measurements of land-surface wetness. Many such top-down studies have associated the abundance of vectors or vector-borne disease incidence with satellite imaging (e.g., Rogers and Randolph, 1991; Hay et al., 1996). Such investigations have generally used vegetation classification or the Normalized Difference Vegetation Index (NDVI), which measures vegetation greenness, as proxies for soil moisture and land-surface wetness. However, the NDVI and other similar indices were designed for monitoring vegetation conditions in large-scale climate studies, and do not capture all the detailed environmental conditions that influence the processes leading to malaria transmission. For addressing the malaria problem, there is need for developing new indices that characterize, among other variables, the fraction of the large area covered by persistent water pools that is suitable as habitat for sub-adult mosquitoes. In order to develop these indices one needs to use remote sensing data (such as products from active microwave remote sensing) that describe the size of the land area covered by water pools. The formation of water pools is affected not only by meteorological conditions such as rainfall and evaporation rates but also land-surface conditions such as topography and soil type.

Key elements to make significant progress in this important research area, as well as other similar areas of multidisciplinary research, would include the following:

  1. Design the integrated observations network to suit the specific research problem at hand, instead of using observations that were collected with the objective of addressing a different research problem; for this project, the hydrologic and climatological sampling are being coordinated with the sampling of mosquito populations and health data so that the spatial and temporal sampling strategies will be comparable.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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  1. Identify the appropriate spatial and temporal resolutions that are needed for characterizing and modeling the interactions within the environment that are critical to answering the research question; this involves sensitivity testing of the model in combination with field study.

  2. Integrate information about the environment from several types of measurements including ground, airborne, and spaceborne measurements. Such integration is best achieved through optimal assimilation of data into appropriate environmental models (see Chapter 3).

  3. Integrate embedded sensors with community-based observations and remote sensing by using database management technologies.

  4. Integrate information on the physical, biological, and chemical environments using a consistent multidisciplinary framework.

  5. Develop a “collaboratory”—a web-based system of data, predictive models, and management projects for access by researchers and users in different fields and with e-mail and chat options for cross-disciplinary discussion.

  6. Incorporate the recent advances in sensor technology, computing technology, geographic information systems, and satellite remote sensing.

Summary

This case study has shown an application of integrated observations to a major global disease that kills millions and infects hundreds of millions each year. This study demonstrates the importance of establishing consistency in the spatiotemporal resolution and locations of four very distinct types of data—in this case data related to climatic conditions, hydrologic conditions, mosquito populations, and malaria incidence. These data exist in part, but they come from observations networks that were designed independent of each other. Without coordination of physical, chemical, biological, and medical data collection at appropriate spatial and temporal extents, and data assimilation and modeling to move across scales and simulate the dynamics of malarial transmission, it would be difficult to infer the controls on malarial outbreaks or the best methods for preventing them.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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CASE STUDY IV
—ACHIEVING PREDICTIVE CAPABILITIES IN ARCTIC LAND-SURFACE HYDROLOGY

Climate change associated with global warming is arguably occurring most dramatically in the Pan-Arctic because, to first order, the forcing of the Arctic water cycle is categorically governed by the phase transition between ice and liquid water. The Pan-Arctic, an area defined by the Arctic Ocean and the lands that drain into the Arctic Ocean, encompasses a significant portion of the Earth’s land area. How the Arctic climate evolves will influence the planetary heat balance and the circulation of the global oceans. Rapid climate warming, expressed as drying soils, rising average temperatures, and melting permafrost, is changing the ecosystem (Olsson et al., 2003), shortening winter access for oil and gas extraction (NRC, 2003), and damaging roads and structures on the tundra (Nelson et al., 2002). Two consequences, transition of tundra as a carbon sink to its being a carbon source (Oechel et al., 2000) and decreasing albedo (Chapin et al., 2005), serve as positive feedbacks to climate warming. Current warming is already having an impact upon the indigenous people of the North. The melting of permafrost presents challenges to infrastructure, rising sea levels are forcing abandonment of some coastal villages, and some traditional hunting and fishing practices are no longer viable (USGCRP, 2003).

The importance of the Arctic water cycle to global processes argues that these processes be well monitored as a means of checking the predictive accuracy of our models and, as humankind begins to manage the global climate, as a means to monitor the effects of our actions. There are currently temporal gaps associated with the difficulty of access to many regions of the Arctic in winter, spatial gaps associated with national willingness or ability to maintain comprehensive monitoring systems, and thematic gaps associated with the emerging comprehension of the impact of climate change in the Arctic. The need for an integrated hydrologic monitoring system in the Pan-Arctic prompted creation of a series of recent research programs. Among these are the international Arctic Monitoring and Assessment Programme (AMAP), the National Science Foundation (NSF) Arctic Research Consortium of the U.S. (ARCUS) Study of Environmental Arctic Change (SEARCH), and, most relevant to this report, NSF’s Pan-Arctic Community-wide Hydrological Analysis and Monitoring Program (Arctic-CHAMP) (Vörösmarty et al., 2001). The overarching theme of these reports is captured in the National Research Council report, Toward an Integrated Arctic Observing Network (AON) (NRC, 2006b). An AON would integrate all relevant physical, biological, and social observing and data management elements to comprise an Earth observing system for the Arctic—essentially the Arctic component of the Global Earth Observing System of Systems (GEOSS). An integrated Arctic land-surface hydrologic observing system would be a subset of the AON.

Both the Arctic-CHAMP and AON proposals are comprehensive and compelling. Both identify remote sensing as an integral element of any Arctic ob-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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serving system. However, neither differentiates among the potential contributions of airborne and satellite sensors, nor identifies the research and supporting infrastructure needed to fully realize the potential of satellite remote sensing. The objective of this case study is to explore a rudimentary strategy for robust remote sensing hydrology in the Pan-Arctic, specifically, to identify capabilities needed to meaningfully link in-situ observations to satellite sensor-scale observations. The assertion here, and as a general assertion of this report, is that the appropriate mechanism for achieving this linkage is through robust models that span the scales of the hydrologic processes.

The report from the workshop defining Arctic-CHAMP observed, “The water cycle of the Arctic plays a central role in regulating both the planetary heat balance and circulation of the global oceans. Recent and unprecedented environmental changes, such as declines in the total area of winter snow cover on land and declining sea ice cover throughout the Arctic Ocean, are now well documented. The causes of these changes and their impact on the global ocean and atmosphere are still poorly understood. The cycle of freshwater in the Arctic land atmosphere-ocean system is central to these observed changes” (Vörösmarty et al., 2001). This same report lists several key unresolved issues, namely:

  • What are the major features (i.e., stocks and fluxes) of the Pan-Arctic water balance, and how do they vary over time and space?

  • What are the hydrologic cycle feedbacks to the oceans and atmosphere in the face of natural variability and global change?

Among the principal recommendations of the report are

  • A substantial commitment should be made to rescue, maintain, and expand current meteorological and hydrological data collection efforts, and

  • An assessment of the feedback mechanisms through which progressive hydrological change influences both the natural and human systems is urgently needed (Vörösmarty et al., 2001).

That is, an observing infrastructure is needed that offers more information about the current Arctic hydrological system at all scales, and captures key aspects of the system’s evolution with climate warming.

Any design of an Arctic hydrologic observing system is constrained by the temporal and spatial scales of processes being observed, and by the difficulty of access in winter, because of weather, and in summer, because of fragility of the active layer. Temporal scales of interest vary from hours, e.g., significant precipitation, to days, e.g., spring melting of the snow pack, to seasons, e.g., melting and refreezing of the active layer. The spatial scales of interest vary from point-scale for intrinsic measurements like temperature or soil moisture, to plot-scale for measurements like moisture fluxes in the active layer, to catchment-scale to relate drainage to topography, to watershed-scale for issues of water balance, to Pan-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Arctic-scales for the global water cycle. An example of an almost integrated Arctic hydrologic observing system would be the sum of the building blocks identified in the AON report. These are the Toolik Lake LTER (point- and plot-scale measurements in three characteristic terrains of Arctic tundra, Figure 4-10), the Imnavait Creek microscale system (a 2.2 km2 headwater catchment), and the Kuparuk River watershed. Each has been extensively instrumented and studied.

Difficult access in winter or summer argues for autonomous sensing stations at point through plot scales, embedded sensor networks for plot through catchment scales, airborne platforms for plot through watershed scales, and satellite remote sensing for catchment through Pan-Arctic scales (Figure 4-11). Elements comprising proven autonomous stations, though not cheap, are commercially available for many key measurements. Satellite instruments have grown in number and sophistication. The weak elements are mature technologies for embedded sensor networks and ready access to airborne sensing technologies. These systems, were they available, overlap the scales of autonomous sensing at the pot-scale end of the scale spectrum and satellite-scale sensing at the other end of the scale. If those robust models that link hydrologic processes at plot-scale to the watershed-scale are to be developed and validated, embedded sensor networks, airborne sensors, and the interpretive skills to integrate the observations with in-situ data and satellite data are essential.

Embedded Sensor Networks

Given the fragility of the active layer and the difficult access, Arctic areas would benefit greatly from the new and emerging sensor technologies described in Chapter 2. Use of in-situ microcosms for measurement of chemical weathering rates has been demonstrated in the Antarctic (Maurice et al., 2002); a combination of static and continuous flow in-situ reactors coupled with temperature sensors and piezometers could be highly beneficial for studying hydrobiogeochemical processes in the active layer of soils and hyporheic zones during the warmer months. Microelectrode sensors, such as those used by Haack and Warren (2003) (Figure 2-3), would be useful for probing biogeochemical processes in tundra soils. Wireless embedded sensor technologies would have the potential to expand tremendously the spatiotemporal resolution of sampling, particularly of parameters such as incident sunlight (including various ultraviolet and visible wavelengths and photosynthetically active radiation) and temperature, both of which are cheap, easy to measure using current technologies, and can be integrated into tiny wireless devices. The mobile networked infomechanical systems (NIMS) tram cable sensor systems for surface-water, soil, and associated microatmospheric sampling shown in Figure 2-8 (Harmon et al., 2006) would be particularly useful to prevent damage to fragile soils and plant communities in locations where stable columns could be safely and reliably emplaced.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-10 Three terrain types found on the Alaskan North Slope. These and the open water of thermokarst lakes comprise the “canonical” terrain types that might be used to characterize the low-relief regions of Arctic tundra. SOURCE: Reprinted, with permission, from England and De Roo (2006), University of Michigan.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-11 Schematic showing the geographical coverage versus response time of different sensing approaches as discussed in the text. The x axis shows how spatial extent of sampling increases from microsensors and in-situ sensors through airborne sensors to satellites, while the y axis demonstrates that the increase in spatial extent can come with a cost (in terms of actual cost and/or in terms of amount of time between design of a system, implementation, and return of data to investigators). A sensor network or sensor web allows increased spatial sampling with less time for deployment and data return, because the sensors are meant to be easily deployable and widely distributed with continuous data feed to web-based platforms. SOURCE: False color satellite image from NASA; microsensors courtesy of L. Warren, McMaster University, Canada; insitu sensors courtesy of E. Boyd and G. Geesey, Montana State University.

Considering the sensitive environment, remote locations, and difficult terrain, a variety of challenges will need to be considered and overcome, such as:

  1. difficulties with battery life and solar recharge systems in cold climates;

  2. need to make systems capable of resisting severe winter conditions, including freeze-thaw, or to emplace and remove seasonally;

  3. environmental considerations; if sensors are widely scattered, for example dropped from airplanes, then the sensors themselves could become a new source of widespread environmental pollution.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Nevertheless, such remote and difficult terrains are some of the prime locations whereby wireless sensor technologies could have the greatest effects on data collection. Key to this will be further development of robust systems and of new types of sensors for a wider variety of biogeochemical parameters.

An Example of a Potential Airborne System for Observing Moisture in the Active Layer

Radiometers operating below the Debye relaxation frequency of liquid water (~10 GHz) are sensitive to moisture in the upper few centimeters of soil (Jackson et al., 1984, 1995; Schmugge and O’Neill, 1986; Jackson and O’Neill, 1987; Schmugge and Jackson, 1992; Njoku and Entekhabi, 1996). Radiometers at 1.4, 6.9, 19, and 37 GHz, among other frequencies, have long been carried on large NASA aircraft to support terrestrial hydrology. A similar remote sensing approach is appropriate for the Arctic, but new digital technologies (Fischman and England, 1999; Fischman et al., 2002; Pham et al., 2005) enable fabrication of compact systems that can be carried by low-cost, Piper Cub-class aircraft. These aircraft can operate with very little maintenance out of unimproved landing strips, which would allow them to support season-long campaigns in the Arctic.

Airborne observations would allow investigations of the scale-dependent distribution of soil moisture that span the spatial gap between point and satellite observations. For example, Advanced Microwave Scanning Radiometer – EOS (AMSR-E), a microwave radiometer currently flying on NASA’s Aqua satellite, produces data that are sensitive to moisture in the Arctic tundra. Figure 4-12 shows plot-scale, microwave brightness observations of tussock tundra during a diurnal cycle for several of the AMSR-E frequencies. Diminished brightness at 6.7 GHz relative to the higher frequencies is a consequence of moisture in the active layer. While this moisture sensitivity is expected, there have not been investigations to quantify the interpretation nor to extend them to the scale of the satellite footprint, ~50 km. Of potentially greater relevance for soil moisture sensing, the European Space Agency Soil Moisture Ocean Salinity (SMOS) mission, being developed for launch in 2007, will be the first satellite to carry a 1.4 GHz imaging radiometer (Kerr et al., 2001). Like AMSR-E, its footprint will be ~50 km. Without investigations of remote sensing signatures of scale-dependent processes between point observations and the SMOS spatial resolution, SMOS data are likely to have limited impact upon our understanding of land-surface hydrology in the Arctic.

An airborne sensor system capable of spanning the point-to-satellite scales is illustrated in the design study shown in Figure 4-13. Digital radiometer technologies enable robust designs of this power, weight, and size, but none have been built for the aircraft environment (Fischman and England, 1999), and no organization has the appropriate airborne platform to carry them. Airborne systems, like that in the design study shown in Figure 4-13, could be used to cali-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-12 Diurnal temperatures at a 350 incidence angle for 6.7, 19, and 37 GHz brightness and for the thermal infrared radiometer (TIR) for tussock tundra. Lower brightness values for the lower frequencies are caused by moisture in the active layer of the tundra—clearly an important parameter for evaluating climate change and carbon cycling in such terrain. SOURCE: Reprinted, with permission, England and De Roo (2006), University of Michigan.

FIGURE 4-13 An Aviat Husky aircraft showing location of radiometers in a pod attached to the float fittings of the aircraft. The design study included 1.4, 6.9, and 19 GHz nadir-viewing, profiling radiometers, and a thermal infrared (TIR) profiling sensor. All sensors have a 17° beamwidth yielding 30 m footprints at 100 m heights above ground. Radiometers were Dicke-capable with two-point calibration and digital detection. 60 kn airspeeds yield 110 ms integration times with a 10 percent footprint smear, a NEΔT of ~0.8 K at 1.4 GHz, and ~0.4 K at higher frequencies. Modified, with permission, from Aviat Aircraft, Inc., Afton, Wyoming.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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brate and validate land-surface models of the energy and moisture fluxes that are being developed for the canonical terrains shown in Figure 4-10. Their data would also help disaggregate the inherently low spatial resolution satellite data for the canonical terrain types within the radiometer footprint. Such systems enable hydrologic process studies at spatial scales that are difficult to capture with point measurements. Relatively inexpensive systems like this address two of the three uses of airborne systems identified in Chapter 2. They enable interpretation of satellite data, and contribute to the science of land-surface hydrology as it occurs in the Arctic. Both are essential elements of understanding and skillfully predicting the rapid evolution of the Arctic climate.

Summary

The Pan-Arctic region is experiencing rapid climate change associated with global warming, expressed as drying soils, rising average temperatures, and melting permafrost. There is a compelling need for an integrated hydrologic monitoring system in this region. This case history has explored some opportunities for hydrologic remote sensing in the Pan-Arctic, with a specific example given for observing moisture in the active layer of the soils. Opportunities range from microsensors and embedded sensor networks through airborne and satellite observations. Given the difficulty of access to Arctic sites and the sensitivity of the Arctic ecosystems, there is a pressing need for these technologies. However, there are also enormous challenges to developing and maintaining in-situ sensors and sensor networks for use under such extreme conditions.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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CASE STUDY V
—INTEGRATING HYDROCLIMATE VARIABILITY AND WATER QUALITY IN THE NEUSE RIVER (NORTH CAROLINA, USA) BASIN AND ESTUARY

Problem Statement and Background Information

This case study focuses on the impact of human activity and hydroclimate variability on nitrogen sources, cycling and export in coastal watersheds, and their impacts on fresh water and estuarine ecosystem health. The problem requires a synthetic treatment of hydrologic, ecosystem, and anthropogenic water, carbon, and nutrient (WCN) processes within a coupled watershed and receiving estuary. The focus was on the Neuse River Basin and Estuary (NRBE) in North Carolina. Nutrient management in the NRBE focuses on nitrogen as the limiting nutrient in the estuarine system, although interactions of nitrogen, phosphorus, and other constituents require an integrated, multicomponent approach.

Over the last two decades, major debates have developed over the condition and management of the NRBE, involving water quality, quantity, agriculture, urban sprawl, and coastal development. Headlines in local newspapers were filled with coverage of massive fishkills in the Neuse and its estuary, harmful algae blooms, the development of anoxic dead zones in the estuary, and their links to watershed runoff and nutrient loading from rapidly expanding industrial hog operations, intensified row crop production, urban sprawl, and renewed hurricane activity. Burkholder et al. (1997) reported a newly discovered dinoflagellate with a complex life cycle including a toxic and predatory stage stimulated by nutrients and other substances as a cause of fishkills and a toxic threat to human health. The popular press referred to Pfisteria piscicida as “flesh eating”, because of the open lesions found on many of the dead fish. Reports of adverse human health responses to direct contact with estuarine water or inhalation of toxins emerged in the Neuse and as far north as tributaries of the Chesapeake. The complexity of the linkages between water quality, anoxia, microbial dynamics and fishkills, uncertainty in causal mechanisms, and general lack of adequate monitoring led to scientific and management controversy. Significant disagreement and debate in scientific publications and the popular press ensued, and an emergent response from state and municipal government, nongovernmental organizations (NGO), and other industrial and community groups developed within a framework characterized by strong positions, but very little observational data. One major source of agreement was that nitrogen loading from the watershed was a prime cause of the lower river and estuarine eutrophication. Since then, significant additional monitoring and sampling has been developed in the estuary, but an integrated sampling plan sufficient to characterize and explain watershed WCN dynamics is yet to develop.

The Neuse is a ~15,000 km2 watershed draining into the Neuse Estuary, part of the Pamlico-Albemarle Sound complex (Figure 4-14). Nitrogen from point

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-14 Location of currently active stream gages in the Neuse watershed, North Carolina.

and non-point sources cycles through multiple media and flowpaths in the atmosphere, surface water, soils, and groundwater as well as the built agricultural, residential, and industrial environment. Complex coupling between the stores and fluxes of WCN and variable hydroclimatic forcing (with record drought and floods in the last decade) create episodic and spatially heterogeneous loading, transformations and export of nitrogen from the terrestrial to the aquatic system. Nitrogen (N) flushing, referring to a build-up of terrestrial nitrogen stores during dry periods and subsequent mobilization during storm events, provides nitrogen pulses on top of chronic loading. Hydrologic state, through soil moisture influence on redox conditions and microbiological activity, is an important determinant of biogeochemical transformations of N. As an example, nitrification and denitrification, the microbially mediated transformation of nitrogen promoted by different redox conditions as influenced by soil saturation levels. Riparian zones, with typically organic-rich, moist soils, are often sites of high denitrification potential, converting nitrate into N2 or N2O gas. However, during dry periods, riparian soils may become aerobic and transform from largely denitrifying to nitrifying conditions, becoming a source of nitrate. Therefore, sources and sinks of runoff and nutrients can be highly variable in space and time, corresponding to “hot spot” and “hot moment” phenomena (McClain et al., 2003).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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River discharge-driven variations in estuarine residence time and nitrogen flushing have been associated with spatial and temporal patterns of estuarine phytoplankton assemblages, repeated algae blooms, low dissolved oxygen events, and trophic system disturbance (Paerl et al., 2006a,b; Burkholder et al., 2004). Efforts to decrease nitrogen entering the NRBE require reductions in N point and non-point sources, as well as increasing ecosystem uptake and retention by best management practices (BMPs). These BMPs include land-use zoning, buffer strips, detention basins, constructed wetlands, stream restoration, and a set of other practices. Non-point sources are difficult to quantify as they are spatially diffuse and episodic, including large confined animal feed operations (CAFO), row crop and residential land use, and atmospheric deposition. A major impediment to the design and implementation of N reductions has been a general lack of understanding of the following:

  1. what the individual and cumulative effects of BMPs are, particularly their performance over the distribution of hydrologic events the area is subject to,

  2. where and when the bulk of N loading and delivery to the river and estuary occurs,

  3. where and when N retention occurs, including storage and transformation into forms that can be later released, as well as denitrification and volatilization loss, and

  4. what the magnitude and timing of river and estuarine ecosystem response would be to specific reductions in nitrogen loading.

The issues described in this section have immediate, practical applications. Regulation of N loading into the NRBE and implementation of BMPs are priorities for municipal, state, and federal agencies charged with protecting fresh water and estuarine ecosystems and resources. The issues and questions are also at the core of the field of ecohydrology, particularly the interaction of hydrologic storage and flux of water with ecosystem material (carbon and nutrient) balances. Progress in these areas are limited by a general lack of modeling frameworks that couple WCN interactions at the watershed scale, as well as observational programs with a sampling regime appropriate to the space and timescales characterizing key processes and feedbacks.

To date, the collection and synthesis of hydrologic and ecosystem information has not been coordinated as part of a centralized informatics system, as contrasted to the South Florida Water District. A set of monitoring programs in the NRBE funded by state and federal agencies are building important data sets on specific aspects of watershed and estuary ecosystems but requires enhanced observational methods, modeling, and institutional support and organization. Progress has been made on integration of diverse information stores through the state coordinated Modeling and Monitoring (MODMON) Project (http://www.unc.edu/ims/neuse/modmon), a prototype (paper) design of a Hydrologic Obser-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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vatory (Reckhow et al., 2004). A more integrated project leveraging on these efforts could take advantage of recent advances in instrumentation, informatics, and modeling to provide a more fundamental understanding of the controls on magnitude and timing of N export, and response of the estuary. Such a project would need to last for a few to several years, in order to sample a range of hydroclimatic conditions with sufficient replication of seasonal dynamics to determine sources, sinks, and variability in the system sufficient to develop and test management options. Longer-term monitoring at reduced intensity would be coupled with distributed models and available remote sensing resources to track and evaluate temporal trends of N cycling and transport in response to management activities, land use, and climate change.

Sampling Strategy

Given the size and heterogeneity of the NRBE, nested sampling is designed to generate ecohydrologic storage and flux information to be scaled to the full watershed with the use of remotely sensed and other spatially distributed information and ecohydrologic models. The nesting would proceed at increasing levels of spatial detail from the full watershed to selected subwatersheds covering dominant land use and geomorphology, and hillslope/riparian systems within the subcatchments. Information required over this scale range includes

  1. Land-use specific runoff quantity, pathways, and nutrient loads in wet-dry conditions,

  2. Residence time, retention, and transformation of N in terrestrial and aquatic systems, and

  3. Interaction of watershed discharge and N loading with estuarine dynamics.

Existing Measurement Capability and Information Synthesis

Currently available instrumentation and informatics in the Neuse are briefly described, and improvements for more efficient use of current technology, as well as new measurement technologies, are proposed following the discussion in Chapter 2. The existing major monitoring networks within the NRBE, and how they could be augmented to address the major research and management questions, are also described.

Much of the large-scale spatial information describing the Neuse (available on-line at http://www.env.duke.edu/cares/neuse/GIS.html) has been incorporated into the Neuse digital watershed (Maidment et al., 2005; Merwade et al., 2005). Figure 4-15 shows the locations of a series of these data layers for different measurements (or centroids for Next Generation Radar [NEXRAD]), each

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-15 Point locations associated with time series objects within an Arc-Hydro digital watershed representation of the Neuse. MonitoringPoints are USGS NWIS streamflow stations, RainStations are National Climatic Data Center (NCDC) rainfall stations, WQPoints are National Water Information System (NWIS) water quality measurement stations, GWPoints are NWIS groundwater wells, RiverNetPoints are water quality stations operated by North Carolina State University (http://rivernet.ncsu.edu), and HRAPPoints contain center points of the Hydrologic Rainfall Analysis Project (HRAP) grid for NEXRAD precipitation estimates. SOURCE: Reprinted, with permission, from Merwade et al. (2005). © 2005 by CUAHSI.

linked to a time series of data values. Additional point feature classes are associated with centroids of the North American Regional Reanalysis (NARR) grid cells, and are linked to time series of 3 hr and monthly simulated meteorological, energy balance, and soil moisture values for the NARR time domain of 1979-2003. Additional information provided by a group of federal and state agencies and universities includes

  1. Surface-water discharge: ~40 active USGS stream gauges and 5-10 additional gages operated by universities.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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  1. Surface-water quality: Sampling of inorganic and organic stream nutrients, pathogens, sediment load, and other water-quality parameters carried out at USGS gages and other state and local sampling sites, typically at quarterly to monthly frequencies.

  2. The Rivernet Program (http://www.rivernet.ncsu.edu): Sampling of water quality at high frequency (1 hr) of water temperature, conductance, pH, NO3, and turbidity on six higher order streams.

  3. Soil moisture/temperature: Rooting depth (0.2 m) soil moisture and temperature are measured at several sites by the North Carolina State Climate Office (http://www.nc-climate.ncsu.edu/cronos/map).

  4. Groundwater measurements: USGS groundwater measurements are typically limited to one measurement at the time of well completion, concentrated in the Coastal Plain. More intensive groundwater monitoring networks include a site with ~66 wells installed and monitored by USGS and North Carolina State Department of Water Quality in a CAFO in the Contentnea Creek subwatershed to study transport and transformation of hog waste-derived nutrients in complex Coastal Plain groundwater systems (Spruill et al., 2004, Tesoriero et al., 2005) and drought monitoring wells.

  5. Atmospheric inputs: National Weather Service (NWS) NEXRAD rain radar systems in Raleigh and Wilmington provide full coverage for the NRBE. The North Carolina State Climate Office operates and distributes meteorological information that report 15-minute to daily precipitation, and min/max temperature collected from a network of different measurement sites (http://www.nc-climate.ncsu.edu) with a subset of sites providing hourly measurements of temperature, relative humidity, precipitation, solar radiation, and photosynthetically active radiation. Dry and wet N deposition are measured and estimated at National Atmospheric Deposition Program and Clean Air Status and Trends Network sites in and around the NRBE.

  6. Estuarine physical, chemical, and biological state: Estuarine monitoring is carried out by state- and federal-funded efforts, including fixed buoy, periodic ship transects (http://www.marine.unc.edu/neuse/modmon) and a novel method of high spatial and temporal frequency measurement carried out in association with the North Carolina Department of Transportation (http://www.ferrymon.org). Physical, chemical, and biological information on the state and dynamics of the lower river and estuary are regularly collected, geolocated and distributed on these sites, and integrated into hydraulic and biogeochemical modeling of the estuary (http://www.unc.edu/ims/neuse/modmon).

  7. Remote sensing information: High-resolution remote sensing products are available that characterize land cover, topography, and estuarine conditions. These include

  1. A high-resolution land-cover classification using recent Enhanced Thematic Mapper, System Pour l’observation de la Terre, and aerial photographic interpretation that has been developed by the U.S. Environmental Protection Agency (Lunetta et al, 2003).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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  1. Annual land-cover change products from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery (http://maps6.epa.gov).

  2. LiDAR elevation data produced by the state of North Carolina, the Federal Emergency Management Agency, and other agencies include statewide bare earth (BE), 20' and 50' elevation grids (http://www.ncfloodmaps.com).

  3. Remote sensing of estuarine and lower river water quality carried out by high spectral resolution airborne imagery (AVIRIS, CASI) detection of chlorophyll and phytoplankton assemblage (Figure 4-16) for selected time periods.

Information Gaps—Extension of Existing Resources

To adequately address the research questions posed above, additional measurement and monitoring of new variables, and extension of current sampling regimes at key scales and locations need to be planned. Reckhow et al. (2004) designed a prototype Hydrologic Observatory sampling scheme for the Neuse supplementing existing monitoring programs, over a scale range that includes major geomorphic zones and land-use conditions in the watershed. The elements of a hypothetical extended network are summarized in Table 4-1. Readily available instrumentation, as well as emerging and envisioned measurement technologies that we expect may be available over the next decade, are both included. The overall goal is to locate individual sensors as part of a multiscale and multidisciplinary observation network. Plot-scale sampling will be clustered within gaged subcatchments, reflecting the theoretical paradigm of the hillslope ecohydrologic models that are used as both a conceptual framework to study N flushing mechanisms and modeling in this case study. Sampling from ridge to riparian zone would capture hydrologic and biogeochemical evolution along hillslope surface and subsurface flowpaths within the drainage areas of small gaged catchments. Sampling along specific channel reaches would investigate in-stream routing and nutrient processing of water from the contributing catchments. In the Coastal Plain, sampling would be arranged along flow gradients accounting for potential lack of correspondence between surface and subsurface flow directions. One gap that would be filled is the addition of small, land-use-specific catchments. The existing network would be expanded following the methods suggested by (Maidment, 2004) using a GIS-driven allocation to develop both nesting and representativeness of the gage network for a desired range of land use and drainage areas. As an example, Figure 4-17 shows percent urban land use in subcatchments in the upper NRBE extracted with a 10-km2 drainage area threshold from the North Carolina LidAR dataset and the land-use classification of Lunetta et al. (2003).

The scale, nesting, and distributed paradigm for information required suggests a specific watershed model framework be used as a synthetic template, analogous to the Everglades Landscape Model (ELM) and South Florida Water Management Model (SFWMM) which are used to evaluate management and

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-16 Spatial relationships between the phytoplankton biomass, as chlorophyll a, and freshwater discharge in the Pamlico-Albemarle Sound estuarine system. Surface-water chlorophyll a concentrations were estimated using an aircraft-based SeaWiFS remote sensing system (Courtesy L. Harding, University of Maryland Center for Excellence in Service), calibrated by FerryMon and ModMon samples. Under relatively low flow and long residence time conditions, phytoplankton biomass is concentrated in the upstream reaches of the estuaries. Under moderate flow, phytoplankton biomass maxima extend further downstream. Under high flow (i.e., short estuarine residence time) phytoplankton biomass maxima are shifted further downstream into the open Pamlico Sound. SOURCE: Reprinted, with permission, from L. Harding, University of Maryland.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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TABLE 4-1 Nested Sensor Design With In-Situ and Remote Sensor Systems Covering Six Orders of Magnitude of Hydrologic and Biogeochemical State and Flux Variables

Length scale

10−1-101 m point – plot time domain reflectometry (TDR), tensiometer

Depth nested through rooting zone

102–103 m

Catchment TDR, tensiometer wireless sensor networks

104–105 m

Regional watershed microwave, thermal remote sensing

Soil moisture and tension

Soil solution chemistry

Tension lysimeters, nitrate microsensorsa through rooting zone

Nitrate microsensorsa, redox probes coupled to wireless sensor networks

 

 

Hillslope transects, over-sampled in riparian zones

 

drainage lysimeters below rooting zone

 

Groundwater level, chemistry

Transducer, grab samples, nitrate microsensorsa/

Well clusters in wireless sensor network—transducer network

GRACE

Wells screened to multiple depths

Hillslope and flowpath transects

Evaporation transpiration

Evaporation pan, Bowen ratio station

Eddy covariance

MODIS visible/NIR and thermal remote sensing estimation evaporative fraction

GOES estimation of net radiation

 

Tower flux systems in multiple land-covers

Standard station height, Below canopy and in clearings

Precipitation and precipitation chemistry

Precipitation gage throughfall collectors wet/dry collector

Precipitation gage clusters throughfall collectors wet/dry collectors

Polarimetric radar, precipitation gage and disdrometer network

Paired gages

 

Runoff and streamflow quantity and quality

Runoff plots

Runoff plots in multiple land use, soils, topographic settings

Stream gage network sampling channel flow/chemical/sediment concentrations from catchments ranging from 10−1–104km2, stratified by major physiographic province/land use, altimetry

lab analysis of storm event water chemistry

 

Nitrogen isotopes

 

 

Real-time reagent analysis, turbidimeter, nitrate microsensorsa

 

 

Monthly lab analysis of fuller chemical and sediment concentration

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Microbial ecology

Hyporheic zone and soils: cell counts with DAPI, enumeration of target taxa with FISHb/

Downstream transects: cell counts with DAPI and enumeration of target taxa with FISHb/

15N analysis

15N addition experiments to small hyporheic zone subplotsc/

Natural 15N and 18O analysis of stream samplesd/

NOTE: NIR = Near Infrared; GOES = Geostationary Operational Environmental Satellites.

aAs per Bendikov et al. (2005); see Chapter 2. Additional micro/nanosensors could be incorporated as they become available and are field tested.

bA suite of different microbial ecologic methods may be used, most likely to include the DAPI staining method of Porter and Feig (1980) to determine total cell counts along with fluorescent insitu hybridization (FISH) for phylogenetic identification without colonization (Amman et al., 1995).

cE.g., Mulholland et al. (2000), Hamilton et al. (2001).

dSee Kendall (1998).

restoration strategies in South Florida. Given the watershed characteristics and the nature of the management problems, these models should have the capability to simulate hillslope and stream reach routing and biogeochemical transformations. This class of model systems would include (but are not limited to) RHESSys (Band et al., 1993, 2001; Tague and Band, 2004), the ecosystem land models (see Costanza and Voinov, 2004, of which the ELM is one example), and a set of distributed hydrologic models to which carbon and nutrient dynamics could be added such as distributed hydrology soil vegetation model (DHSVM) (Wigmosta et al., 1994), Real-Time Integrated Basin Simulator (tRIBS) (Ivanov et al., 2004a, b), TOPMODEL-based Land Atmosphere Transfer Scheme (TOPLATS) (Famiglietti and Wood, 1994), and others. The set of models could also be used to develop instrument deployment strategies based on expected value of additional measurements and testing of simulated behavior as specific hypotheses. In all cases, simulation modules addressing biogeochemical transformation within the channel network would require refinement and coupling to the nested watershed modules at appropriate scales.

Estimation of Hillslope/Riparian Connectivity, Transformations, and Transport

Within the drainage areas of the small, gaged catchments as well as representative areas draining directly into larger reaches, sampling is designed to assess the connectivity and development of organized moisture and shallow groundwater patterns. These properties are seen as a key factor controlling runoff production (e.g., Western et al., 1999) and transport of nutrients (Band et al.,

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-17 Land use for the Upper Neuse River Basin with 10 km2 threshold subcatchment partitioning.

2001). Soil moisture and tension would be monitored at multiple depths along topographic flowpaths in representative land uses in each of the NRBE geomorphic zones. In order to assess the flushing mechanism hypotheses, sampling spatial and temporal frequency in wireless “intelligent” sensor network design would be designed to increase prior to and following recharge events as indicated by precipitation gage and radar networks. Sufficient sampling density would be carried out to estimate mean and variance of soil moisture conditions within areas commensurate to coarse resolution satellite sensors (e.g., MODIS TERRA and AQUA/AMSR) for calibration of remotely sensed moisture patterns.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

Riparian groundwater wells at the downslope terminus of these transects would monitor groundwater level and gradients to determine connectivity and flux of hillslope or riparian water stores to the streams. Sensors recently developed to continuously monitor soil redox potential (e.g., Vorenhout et al., 2004) would be deployed in transects parallel to the wells, and both sets of sensors would be configured as part of the wireless soil water sensor system. These wireless and automated sensors would be complemented by periodic tracer experiments under different wetness and flow conditions designed to estimate hydrologic connectivity between upland, riparian, and stream/river channels of water and material constituents.

Additional geophysical tools need to be utilized to map soil and bedrock structure (e.g., ground penetrating radar) that influence the structure and transience of subsurface flowpaths. It is expected that these applications may be much more difficult due to current high uncertainty of subsurface flowpath patterns and high-frequency variations in actual patterns, but intelligent, wireless design may be useful to trigger the periodic mapping and sampling necessary to understand their transient dynamics. A particularly interesting application would involve the pore-scale nitrate sensor technology described in Chapter 2, extended to include other N species and coupled to the dissolved organic carbon and redox sensors to measure the timing, conditions, and rates of N transformations in upland and riparian nodes along transient hillslope flow networks.

Measurement Along Hydrologic Flowpaths

Novel assessment of groundwater/surface-water interaction along flowpaths in specific stream and hillslope flowpaths would extend the current set of sites to sample evolution of runoff and stream-water across the order-of-magnitude scale range. New technology for rapid, automated sampling of streamwater nutrient concentrations and transformations would be collocated with a larger subset of the stream gage network to compute concentration-discharge relationships and loads. These methods would be designed to detect and quantify denitrification and other transformation rates within reaches. Reaches would be chosen to sample dominant land-use and geomorphic conditions over a range of catchment drainage areas. Existing and emerging technologies that could be used include

  1. Use of fiber optic cables along stream reach bottoms to estimate benthic water temperature with high precision and high spatial resolution (Selker et al., 2006) to map areas of upwelling tied to local hydrogeologic and fluvial geomorphic form and flow patterns to target measurements of water biogeochemical properties along the reach.

  2. Instrumentation for real-time measurement of nutrient concentrations to monitor stores and fluxes of specific nitrogen species, as well as conservative trac-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

ers through stream reaches as targeted by the stream bottom water temperature patterns and bed configuration. New technologies that have recently emerged include wet chemistry analyzers (e.g., http://www.lachatinstruments.com/products/qcfia), ultraviolet nitrate sensors (in-situ ultraviolet spectrometer—ISUS, MBARI), and multi-parameter sondes. In addition, field-deployed mass spectrometers are becoming available that would also determine oxygen and nitrogen isotopic signatures of evolving streamwater composition.

  1. In larger, low-gradient river reaches, Membrane Inlet Mass Spectrometry (MIMS) can be used to gain integrated measurements of flowpath denitrification over heterogeneous reach conditions as demonstrated by McCutchan et al. (2003).

Characterization of the hyporheic environment in each of these reaches would be carried out to provide details of reach hydraulic and biogeochemical conditions associated with downstream evolution of streamwater chemistry and used to develop relationships with easily observed geomorphic and biological stream and riparian variables. Existing and emerging sensor technologies that would be useful for these purposes include

  1. In-situ microcosms and continuous flow reactors to determine biogeochemical transformations of nitrogen and associated reactants.

  2. Micro- and nanosensors to characterize biofilm composition and activity in hyporheic zones. These methods are still in development phase (especially for aqueous systems) but would provide the potential to estimate spatial and temporal variations in microbial dynamics in hyporheic and riparian zones within and between stream reaches.

  3. Coupling of (1) and (2) above with characterization of microbial community structures in stream and hyporheic zone environments to determine the microbial effects on nitrogen cycling (e.g., Maurice et al., 2002).

  4. Nitrogen enrichment experiments (e.g., Gooseff et al., 2004) and nitrogen isotope (N-15) tracer studies (e.g., Peterson et al., 2001) to determine rates and mechanisms of N cycling in streams and to differentiate autochthonous versus allochthonous N sources.

Summary

The design of a program following this case study integrates a nested measurement and monitoring system that samples at spatial and temporal scales appropriate to the coupling of WCN cycling, transport, and retention processes. In contrast to the Everglades case study, there is not a centralized institutional coordination for research and management in the Neuse, other than collaboration between federal and state agencies, as well as local universities and a set of nongovernmental organizations.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

The geographic scale and complexity of this case study is intermediate to the typical principal investigator or small-team investigations and the national-scale environmental observatories (e.g., CUAHSI, CLEANER, NEON). It envisions a finite period of more intense instrumentation to test specific hypotheses regarding N sources, sinks, and transport, and to calibrate remote sensing and distributed modeling of WCN dynamics in the NRBE, followed by less-intensive but long-term in-situ instrumentation, remote sensing and modeling methods in support of watershed management.

To summarize, the NRBE is currently the site of a comprehensive set of measurement and monitoring efforts of federal, state, and local agencies, as well as the several universities in the area. To integrate and coordinate these efforts into a framework to better support the major hydrologic science and management issues, additional activity could include

  • Development of an integrated information system that could access information generated by the diverse set of research and management entities and synthesize the information into a framework emphasizing spatiotemporal trends in WCN storage, flux, and residence time.

  • Further development and integration of a nested monitoring and measurement system that incorporates in-situ sensor networks and is adaptable to spatial and temporal events.

  • Parallel evolution of spatially distributed modeling approaches capable of resolving processes at scales commensurate with the sensor network and designed to characterize both continuous and episodic events. These models would serve as conceptual and operational frameworks for watershed system behavior, would be continuously tested and evolved by the observational network, and would be designed to assimilate information generated by the full sensor network estimation of system state and flux variables.

  • Incorporation of human individual/institutional activity as integral components of the watershed. This is necessary to develop a management model capable of forecasting both short-term and long-term response of environmental policy and regulatory activities. The instrumentation technologies discussed here would need to be matched by social science research instruments to investigate controls and factors influencing individual and institutional behavior relative to WCN cycling and transport in multiple societal and geographical sectors.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

CASE STUDY VI
—MOUNTAIN HYDROLOGY IN THE WESTERN UNITED STATES

A number of recent documents, including Water 2025: Preventing Crises and Conflict in the West (U.S. Department of the Interior, 2005), highlight the need for new water information to enable better decisionmaking for water resources management, and for the myriad of other decisions that are influenced by water. Mountains are the primary source regions for water across the West. Challenges of complex topography, limited access, and large distances in mountains mean that new approaches to measurement of hydrologic properties, beyond those now in use, are needed to estimate spatial hydrologic variables and drive the next generation of predictive models. Integrated measurement systems that combine representative local but accurate ground-based data with broad spatial coverage from satellite remote sensing will be essential.

The demand for water information is large and growing. Western states, more than the rest of the country, depend on the judicious allocation of their water resources to support their industry and increasing population. For example, rivers draining to the California Bay-Delta, through a network of reservoirs and other hydraulic works, provide two-thirds of California’s drinking water, support the $1.4 trillion state economy, and irrigate 7 million acres of the world’s most productive farmland. The region is home to 130 species of fish, 225 species of birds, 52 types of mammals, and 400 plant species (California Bay-Delta Authority, 2000). In addition, the network of reservoirs on rivers draining to the Delta protects millions of people in major California cities against flood disasters.

Real and Emerging Problems

Explosive population growth and changing climate have combined to create mismatches between water supply and demand across the West. Mountain snow pack, the main source of the West’s water resources (Figure 4-18), is particularly vulnerable. Water stresses are pervasive, affecting freshwater and coastal water quality, ecosystem/forest health in Arizona, Sacramento- San Joaquin Delta levee failure, groundwater mining for irrigation in California’s Central Valley, and forest-fire occurrence across western forests, to highlight just a few phenomena. As water becomes a more valuable commodity, more accurate information than is currently available to support estimates of natural-water reservoirs (e.g., snow pack, groundwater), understanding of fluxes (e.g., evapotranspiration, groundwater recharge), hydrologic forecasting (e.g., water supply, floods, droughts), and decisionmaking is not just essential but critical. The technology in current use on these problems is decades old, and the blueprints for modernization are in most cases lacking.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-18 Persistence of snow-covered area in the Colorado River Basin, western United States over the 1995-2002 period for March and April, reported as number of years each 1 km2 Advanced Very High Resolution Radiometer (AVHRR) pixel had detectable snow cover during that month. Snow pack, which covers a relatively small fraction of the basin, provides over 85 percent of the annual discharge in the Colorado River. SOURCE: Reprinted, with permission, from Bales et al. (2008). © 2008 by the American Geophysical Union.

While research challenges span water issues in the West, the potential for integrated observation systems involving new measurement technologies to impact these issues is perhaps greatest in mountain hydrology (Bales et al., 2006). In the mountains of the western United States, sharp wet-dry seasonal transitions, complex topographic and landscape patterns, steep gradients in temperature and precipitation with elevation, and high interannual variability make hydrologic processes and variations significantly different from lower-elevation regions or those that are humid all year. Hydrologic feedbacks in mountainous regions control the availability of water, influence the distribution of vegetation, dominate biogeochemical fluxes, and contribute to global and regional climate variability. Snow in mountains of the West is the main source of the region’s water, with downstream hydrologic processes (e.g., groundwater recharge) and interactions with ecosystems controlled by processes at higher elevations.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

Despite the importance of mountain regions to the hydrologic cycle, the processes controlling energy and water fluxes within and out of these systems are not well understood. Further, the lack of integrated measurement strategies and data/information systems for hydrologic data hamper improvements. As examples, we lack a robust framework for accurately describing and predicting the partitioning of snowmelt into runoff versus infiltration and into evapotranspiration versus recharge (Figure 4-19), and we lack strategies to exploit emerging technology to more accurately measure the spatial variability of snow cover and soil moisture in the mountains. The volume of mountain-block and mountain-front recharge to groundwater and how recharge patterns respond to climate variability are poorly known across the mountainous West (Earman et al., 2006; Wilson and Guan, 2004).

Three aspects of the mountain water cycle in the western United States are used to illustrate the needs and opportunities: (1) precipitation and microclimate, (2) snow pack, and (3) soil moisture. In each of these, researchers must determine the optimal sampling strategy based on such considerations as cost versus resources, reliability, effectiveness, variability of the parameters in question, sensitivity of models to the given parameter(s), potential for new methods to make a substantial impact, and needs of regulators and managers. One important application for this new knowledge is illustrated, hydrologic forecasting, including the water/energy cycle coupling and data integration needed for the emerging generation of forecast tools.

Microclimate and Precipitation

Microclimate can vary substantially at a scale of meters in the mountainous West, with large diurnal fluctuations. Direct measurements of precipitation in mountain environments are particularly challenging, because of the need to cover a large range of elevations and orographic positions. Mountains often have too much topographic variability to effectively use the Doppler Radar systems that have proven useful for monitoring extent and intensity of precipitation throughout the Midwest. Moreover, much of the precipitation falls as snow, and precipitation gages catch too little of the snowfall. Although it is possible to infer snowfall rates from snowpack accumulation measurements, direct observations of precipitation are needed for research (for example, to explore changes in precipitation type [e.g., Knowles et al., 2006] associated with climate variability and change), and for applications, such as to drive flood forecasts.

The spatial patterns of precipitation in mountainous terrain are nearly impossible to measure at the resolution of basin-scale hydrologic models (e.g., ~1 km). The primary ground-based resources available to estimate these patterns are several existing, overlapping networks, including NWS cooperative stations, RAWS (Remote Automated Weather Stations), USDA SNOTEL (Snowpack Telemetry) stations, and some smaller networks. Most of these stations lack the

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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FIGURE 4-19 Schematic of the inter-related fluxes comprising the mountain water cycle, and partitioning of snowmelt. Photograph courtesy of Noah Molotch, University of California, Los Angeles.

capacity to differentiate snow from rain. The National Weather Service installed the Next Generation Radar system (NEXRAD) in 1994 to improve operational measurements of precipitation around the country. However, NEXRAD signals are occluded by mountains and thus are less reliable in the complex terrains where snowfall occurs. Even where precipitation is measured in situ, wind effects limit measurement accuracy. Traditional precipitation gages catch too little snow and cannot discriminate solid from liquid precipitation; when they catch snow, the measurement typically registers when the snow caught by the gage melts, not necessarily when it falls, causing a temporal lag.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

Satellites offer an advantage over the operational radars in producing spatially distributed estimates in mountainous areas due to the unobstructed field of view. The high spatial and temporal resolution of precipitation estimates and the short latency of data availability make geostationary satellites the platform of choice for operational applications. However, microwave data from polar orbiting satellites or combinations of data from geostationary and polar orbiting platforms offer more reliable estimates for applications for which coarse resolution and long data latency are not of concern (Anagnostou, 2004). Distinguishing snowfall from rainfall remains a significant problem in satellite precipitation estimation, with current approaches relying on temperature thresholds or on the use of microwave satellite sensors (e.g., the Advanced Microwave Sounding Unit—AMSU).

A network for mountain precipitation, along with associated microclimate measurements important for determining energy fluxes and energy/water interactions, would ideally take advantage of both strategically placed ground sensors and satellite-based (or airplane) remote sensing. However, a major limitation is the availability of accurate precipitation sensors for remote deployments. Other components of microclimate should be measured spatially using a combination of a relatively few well-instrumented conventional measurement stations that offer low spatial resolution but multiple types of well-calibrated and conventionally accepted measurements, complemented by widely distributed embedded sensing devices that greatly increase spatial sampling resolution, but with cheaper probes and fewer types of measurements. For example, temperature and solar radiation (at a variety of wavelengths) probes can be attached cheaply to a microprocessor with radio transceiver and solar battery for wide distribution in a sensor network. For integrated, comprehensive, water balance measurements, at least some of the sensor nodes should be equipped with additional measurement devices such as wind speed and direction measurement; atmospheric moisture sensors, snow, soil moisture and temperature and other sensors. Installing these sensors in an embedded sensor network would help to control more complex sensing devices, to “flag” events in real-time for greater attention by researchers or managers, and to interact directly with models and control devices. Use of digital cameras to visualize the snowline and weather conditions, and potentially to read gages, is feasible provided icing can be controlled.

Scientists must often assess the trade-off between more expensive but potentially more labor-intensive measurements of a wide variety of parameters versus highly distributed inexpensive sensors for fewer parameters, some of which may be at lesser precision and accuracy. Given the physiographic variability of mountains, network design that encompasses both types of sampling strategies, along with remotely sensed information, is likely to result in significant success (Figure 4-20). It will be important to use remotely sensed data in the initial sampling network design, and as a potential independent method of data validation and verification. On the other hand, the sensing network should help to ground-truth remotely sensed information. Together with modeling, the combination of methods will provide a strategy for merging data at different scales, hence maximizing spatial and temporal resolution. Models can also help guide measurement design.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-20 Conceptual design and deployment of instrument clusters in a mountain basin, integrating satellite remote sensing with strategically placed ground measurements. Selected instrument clusters are anchored by an eddy-correlation flux tower extending above the forest canopy, with ground measurements extending 1-2 km from the tower. Other clusters would consist of sensors and sensor networks but not a tall tower. Adapted, with permission, from Conklin et al. (2006). © 2006 by the American Geophysical Union.

Special consideration will need to be made for engineering embedded sensor pods for harsh and variable mountain conditions, and to designing the sensor network in concert with the topographic challenges (e.g., appropriate relay stations to get around obstacles to wireless communication). In some locations, there may be the need for sensor network data from an array of local sensors to be stored on-site for periodic download rather than telemetered directly to the observer.

Snowpack Properties

Hydrologic and land-surface models are increasingly including mass balance and physically based snowmelt models (e.g., Cline et al., 1998). While several of such models are being used by the research community, improvements in the treatment of snowmelt as well as other model components depends on data. For snowmelt, data needs include spatially distributed components of the surface energy balance, as well as snow properties (Figure 4-20). Ground observations of snow water equivalent (SWE) have been used in conjunction with remotely sensed snow-covered-area (SCA) data to estimate the spatial distribution of SWE across mountainous watersheds (Fassnacht et al., 2003). However, such efforts cannot be expected to yield representative measures of snow distribution across a basin owing to the non-representative location of SWE measurements (Molotch et al., 2006).

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

Several sources of seasonal snowcover data exist, ranging from information collected as part of weather monitoring to hydrologic data from networks dedicated to snow data collection, and more recently to remotely sensed products from polar orbiting and geostationary satellites. Remote sensing is the only practical way to measure the spatial extent and variability of snow cover and albedo, and, during the past decade, methods for mapping snow-covered area from visible and infrared instruments on satellites have become well developed (Dozier and Painter, 2004). However, none of the satellite data sets encompass enough system interactions to be considered “snow system” data (Bales et al., 2006). Snow water equivalent is measured at over 1700 points in the Western United States, from a combination of manual snow surveys and transmitting snow pillows. While this large number of samples provides regional knowledge of the spatial distribution of SWE, it is insufficient to resolve the variability of SWE and snowmelt at the basin scale (Figure 4-21). Moreover, most of snow courses and automated stations are situated on flat or nearly flat terrain, and are preferentially placed high enough to that they stay snow covered most of most winters (to justify the expenditures), which means that we are largely blind at altitudes where snow pack is more ephemeral. Also, there are no stations at the highest elevations, which contribute most of the late-season snowmelt. Glaciers, which also help sustain baseflow after seasonal snow has disappeared, are also severely undersampled. The existing snow measurements are used as indices of streamflow, rather as direct measurements of basin-scale snow volumes.

A comprehensive snow-measurement network would blend sparse but detailed, accurate measurements of snow water equivalent, microclimate, and other water-balance variables with satellite remote sensing and spatially extensive lower-cost measurements of snow depth and other low-cost sensors. The ground-based system would ideally be composed of low-cost sensors in embedded sensor networks (Figure 4-22) that build outward from existing ground-based snow pillows and snow courses to capture the physiographic variability across a catchment (Molotch and Bales, 2005, 2006). Building outward from existing measurement sites takes advantage of their long and valuable record of measurement, and provides the additional measurements needed to use distributed depth measurements. As snow density varies much less spatially than does snow depth (Molotch et al., 2005), many more depth than SWE measurements are needed. Low-cost temperature sensors can also be used to infer snow depth, and other technologies are under development. Satellite data can reliably and accurately provide SCA information. Various interpolation and modeling strategies are available to blend the ground-based SWE and satellite SCA to provide basin-scale estimates of SWE for predictive modeling. Periodic SWE measurements from aircraft platforms can also contribute to this mix (e.g., gamma ray sensors). Thus snow properties are an excellent example of how relatively modest investments in integrated observation systems can immediately provide critical data products.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

FIGURE 4-21 Contributions of various 300 m elevation bands to snowmelt in Merced River Basin, Sierra Nevada, California. Data derived snowcover depletion based on MODIS satellite data. Fraction of basin in each elevation band is given for reference. Continuous, ground-based snow measurements are limited to three sites in the basin (2100-2500 m elevation). SOURCE: Reprinted, with permission, from Bales and Rice (2006). © 2006 by the American Geophysical Union.

FIGURE 4-22 One pod in a sensor web that was installed to measure snow depth over a 20,000 m2 study area in Yosemite National Park. Depth sensor is on right and wireless pod on left. Photograph courtesy of Margot Wholey Photography.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

As satellite radar retrievals of SWE advance, they will and can be integrated into the spatial interpolation schemes developed around the in-situ network. However, for the foreseeable future, there are no operational radar satellites with sufficient spectral and polarization capabilities to infer snow water equivalent in the mountains. A ground-based observational network remains an important component of the snow observing system that will not be replaced by the satellite system because of inherent uncertainties in retrievals. Satellite-based snow cover/depth observations might cover the future needs of some users of snow data, but economics and scientific objectives now require a merging of all available snow information in an enhanced data set. Judicious and strategic extensification of in-situ measurements to lower and higher elevation sites coupled with advancements in remote sensing acquisitions will provide the means to a long-term, high-resolution monitoring of snow pack properties.

Soil Moisture

Soil moisture is a primary state variable of the land surface. In mountains, soil moisture is greatest following spring snowmelt and lowest in late summer and fall after the soil dries. Its spatiotemporal variability affects surface and subsurface runoff, modulates evaporation and transpiration, determines the extent of groundwater recharge, and initiates or sustains land surface-atmosphere feedbacks. Soil moisture is influenced by: (1) precipitation history, (2) soil texture, which determines water-holding capacity, (3) land-surface slope, which affects runoff and infiltration, and (4) vegetation, land cover, and bedrock slope/depth, which influence evapotranspiration and deep percolation. The partitioning of soil moisture to groundwater recharge, evapotranspiration, and surface/subsurface runoff at different spatiotemporal scales and under different hydroclimatic conditions poses one of the dominant challenges in quantifying water cycle variability (Jacobs et al., 2006).

Soil moisture is measured at some RAWS and SNOTEL sites, but these generally do not lie in mountain settings. Remote sensing of soil moisture is made in the microwave frequencies.

As in the case of SWE, passive microwave retrievals of soil moisture are too coarse for the spatial variability and rugged terrain in mountain regions. Radar retrievals of soil moisture (and SWE) are in research mode now but again the lack of an operational radar satellite presents a significant obstacle to the implementation of these retrievals (Shi et al., 2002; Oldak et al., 2003; Western et al., 2004). Moreover, rugged terrain and vegetation cover can confound retrievals. While the technical difficulties are great, definition of the spatial variability of soil moisture is critical in modeling hydrologic response in mountain catchments (Zehe and Blöschl, 2004).

The strategy for measuring soil moisture in mountain catchments mirrors that for snow depth, that is, design a network that captures the spatial variability

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
×

in physiographic features (e.g., north- versus south-facing), plus distance from trees. A number of low- to moderate-cost soil moisture sensors are available that can be incorporated into sensor networks, and new technology is emerging. As radar retrievals of soil moisture advance, they should be integrated into the spatial interpolation schemes developed around the in-situ network. Like SWE, proper network design for soil moisture measurement remains a research issue.

Data Integration and Applications

An additional, more-general challenge that cuts across all aspects of water in the West is that of data integration. Current computing environments, investigator-specific research practices, and agency data distributions are disjoint and do not readily facilitate system/data integration. Typically, these systems use ad hoc scripts to perform the required processing and idiosyncratic naming conventions for the files that hold the products. Data extraction from a variety of systems is, therefore, time-consuming and subject to error proliferation, especially when assembling a synoptic view or parsing the data according to a suite of criteria (e.g., data from all snow courses above some particular elevation in a particular basin with more than some threshold length of record). Our current modes of analysis usually require reorganization of data and creation or rediscovery of metadata values for each product. Dissemination, especially where custom processing such as subsetting, reprojection, or reformatting is required, is often treated in a similarly ad hoc fashion. The technologies to solve most of these problems are at hand already, but implementation will require a concerted, collective commitment by users and providers (Bales et al., 2006).

Cyberinfrastructure advances can overcome many of the current data problems by making data and information available in ways that are convenient for users. That does not necessarily mean that data are made available to users in the same way that they access data now. Rather, technologic advances that are tailored to be responsive to community needs can both make users more cyber-savvy and information more accessible.

Hydrologic forecasting is used to illustrate the role of new, integrated measurement systems. Hydrologic forecasting methods for operational management are well established, and are based on several decades of historical data from sparse networks that monitor surface precipitation and temperature, snow pack, and river stage or discharge. Specifically, flow-forecast reliability and accuracy depend critically upon the use of historical data to calibrate the operational hydrologic models for the watersheds of interest (Fread et al., 1995; Finnerty et al., 1997) and upon the use of reliable quantitative precipitation forecasts (Olson et al., 1995; Sokol, 2003). However, forecast skill for spatially distributed flow forecasts over small areas in the populous coastal mountainous basins or for seasonal forecasts of reservoir inflows in large reservoir projects on the Sierra Nevada is in many cases poor for effective emergency and water supply management.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Long-range reservoir inflow forecasts depend largely on long-range forecasts of surface climatic variables (temperature and precipitation). Nevertheless, reliable estimation of forecast uncertainty for such long-range forecasts will benefit directly from improved good quality hydrologic observations, and recent integrated forecast-management demonstration projects show that reliable forecast uncertainty is necessary for improved reservoir management (Yao and Georgakakos, 2001; USACE, 2002; Georgakakos et al., 2005). The improvement of flow forecasts over small areas will require improvements in high-resolution measurement technology for precipitation and temperature (NRC, 2005) and the use of real-time flow-forecast assimilation procedures (Seo et al., 2003). Here again, good quality data will contribute directly to improved emergency management effectiveness. In addition, future conditions (e.g., warmer temperatures, snow-to-rain transitions) are expected to be outside the range of past system behavior. Several recent studies find evidence that climatic impacts on western water resources are in transition to a new regime (Stewart et al., 2005). This would make large improvements in hydrologic observations and information even more important.

Summary

Mountain snow pack is the main source of the American West’s water resource. However, this resource is particularly vulnerable to ongoing spatial and temporal changes in melt patterns, which will directly affect the seasonal availability of water to the multitude of stakeholders in the region. Three aspects of the mountain water cycle in the western United States were used to illustrate the region’s needs and opportunities: (1) precipitation and microclimate, (2) snowpack, and (3) soil moisture.

The integration of many types of observations can assist the management of mountainous water resources. In most cases, the resulting data and information need to be continuous, reliable, and rapidly available for effective prediction and management. For these reasons, effective strategies such as the use of embedded sensor network technology would contribute greatly to the progressive use of new data sources and types in the water resources management process and for quantifying their benefits and associated costs. The organization and careful monitoring of prototype demonstration projects with the participation of measurement specialists, scientists (including communication and computer scientists), forecasters, and managers is an effective means to develop and test such strategies.

To summarize the chapter, the six case studies presented above are located in climatic regions from subtropical to semiarid to alpine highland to circum polar. They range from large scale to medium scale, and from programs that are largely ongoing to initiatives that are nascent or proposed. Some are more oriented toward scientific understanding; others are oriented toward improving man-

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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agement decisions. Because of this, they provide a wide variety of lessons for government agencies, academic institutions, and even the private sector. These lessons are summarized and discussed in the following chapter.

Suggested Citation:"4 Case Studies on Integrated Observatories for Hydrological and Related Sciences ." National Research Council. 2008. Integrating Multiscale Observations of U.S. Waters. Washington, DC: The National Academies Press. doi: 10.17226/12060.
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Water is essential to life for humans and their food crops, and for ecosystems. Effective water management requires tracking the inflow, outflow, quantity and quality of ground-water and surface water, much like balancing a bank account. Currently, networks of ground-based instruments measure these in individual locations, while airborne and satellite sensors measure them over larger areas. Recent technological innovations offer unprecedented possibilities to integrate space, air, and land observations to advance water science and guide management decisions. This book concludes that in order to realize the potential of integrated data, agencies, universities, and the private sector must work together to develop new kinds of sensors, test them in field studies, and help users to apply this information to real problems.

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