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1
Introduction
THE ADVANCED HYDROLOGIC PREDICTION SERVICE (AHPS) SOMETIME IN THE NOT-SO-
DISTANT-FUTURE....It has begun to rain throughout the Susquehanna River basin, and forecasts call for several
days of rain due to a low pressure system stalled over the region. Warmer temperatures throughout the East have
caused rapid melting of the heavy snow pack at high elevations. Emergency managers throughout the region have seen
conditions like this before, sometimes with resulting floods and other times not. Two county emergency managers check
the National Weather Service (NWS) AHPS website to get a flood forecast for the upcoming two weeks. In one
watershed, inundation maps project a 50 percent chance of significant flooding, but no flooding is predicted in the other
watershed. Evacuation procedures are reviewed and plans made, with a timeline for taking specific actions, as the time
draws nearer. The emergency managers check AHPS several times a day as they put their plans in motion. Forecasts
have been accurate and consistent for two days, confidence in the forecast is increasing, and industries in the floodplain
are prepared to take flood-mitigating actions. Reservoir managers begin to alter their operations by increasing their
flood control storage and releases in anticipation of expected flood flows.
***
Weather and climate have strong and sometimes destructive impacts on lives, livelihoods,
and property. Of all weather-related hazards in the United States, floods are by far the most
devastating: they claim hundreds of lives and cause billions of dollars in damages each year (NHWC,
2002; NOAA, 2001). Less dramatic, but perhaps even more serious in the long term, droughts
impact vast areas of the United States sometimes for many years at a time, causing shortages of
water, diminished water tables, damaged crops and other vegetation, outbreaks of noxious insects
and other costly damages. As climate warms, the hydrologic cycle is likely to become more active,
with more frequent and more severe occurrences of floods and droughts. It is crucial for people's
health, safety and prosperity to understand connections among climate, weather, and the hydrologic
cycle and to use this understanding to make accurate predictions of floods and droughts to
efficiently manage water resources.
Society's health, safety, economic, social, and environmental needs depend on accurate
descriptions and prediction of hydrologic events across a broad range of time and space scales.
Early awareness of the timing, duration, and intensity of hydrologic events contributes to better
understanding and can allow people to anticipate and respond in ways that mitigate the damage, and
more importantly, save lives.
FLOOD LOSSES IN THE UNITED STATES
Two types of floods can occur. Flash-floods are the most rapid flood events that can
develop very quickly after the onset of heavy precipitation. This short window of time provides
limited response time to mitigate losses. Slow-rise floods can produce extensive damage over longer
periods of time, but often allow enough time for evacuations and other mitigating measures.
Regardless, all floods can result in damage to large- and small-scale infrastructure, disruption of
business activity, property damage, and most regrettably, loss of life.
8
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Introduction 9
The NWS hydrologic forecasts and warnings are effective in reducing flood damages in the
United States (NHWC, 2002), and downward trends are visible in deaths attributed to floods. From
1970-2000, 3,829 deaths were attributed to floods; 128 deaths is the annual average (NHWC, 2002).
Three 10-year cycles show a trend of reduced deaths: 1971-1980, 175 deaths; 1981-1990, 112; and
1991-2000, 91 (NHWC, 2002).
The recurrence of floods has remained relatively steady, flood-attributable deaths have
declined, and the economic damage caused by floods has increased markedly in the last century
(Institute for Business and Home Safety, 2001). This increase is due primarily to population growth
in flood-prone areas, such as low-lying floodplain and coastal areas. In the 20-year interval between
1981 and 2000, the average amount of flood damages in the United States was $4.3 billion annually
(Stallings, 1997). The average annual flood damage for 1981 1990 was $3.2 billion and $5.4 billion
for 1991-2000, which includes the record-setting floods of 1993 on the Mississippi River ($18.4
billion in damages) (USACE, 2000). The NWS is working to continue to reduce flood damages
through the enhancement of hydrologic forecasts, warnings, and services.
HYDROLOGIC SERVICES
Hydrologic services are products that provide technical information that can be used in
water resource management, water rights administration, water planning, and water resource
protection1. Hydrologic services enhance or complement the usefulness of weather forecasts with
new hydrologic science; hydrologic techniques developed for operational use; and advanced
hydrologic products (i.e., river stage forecasts, flood inundation maps) that meet user needs.
As demands for hydrologic services evolve and rapidly grow more complex, the stakes of
meeting those demands (whether expressed in terms of public safety, or dollars, or environmental
and ecosystem protection) continue to escalate. Useful descriptions and hydrologic predictions rely
on (1) science and technology; (2) the ability to communicate the information to those who need it;
and (3) the timing and relevance of the information to the end users.
Uses and users of hydrologic services and products form a large and growing contingent. A
broad set of users from agriculture, transportation, energy and water management, emergency
management, and infrastructure planning rely on hydrologic information to mitigate damage from
floods and droughts and make decisions that save lives and property, and add billions of dollars to
the economy each year (NHWC, 2002). The most useful hydrologic services support forecasts that
facilitate primary goals of water supply reliability, potability, and affordability and achieve high levels
of timeliness and accuracy (Rayner et al., 1998). Decisions for efficient water resource use are
increasingly based on hydrologic forecasts across wide-ranging temporal (day-to-day, seasonal, inter-
annual, decades and longer) and spatial (local, regional, continental) scales. This diversity of needs
and services requires a variety of hydro-meteorological and hydro-climate forecasts.
Damages from droughts not withstanding, the needs for timely and accurate hydrologic
predictions most strongly relate to floods and fast rising river levels. The lead-time for mitigating
flood damages is much shorter than that of mitigating and planning for circumstances of drought;
for this reason, AHPS and other providers of hydrologic services most often emphasize accurate
hydrologic predictions for flooding scenarios.
Hydrologic services in the United States predate World War II. In 1940, the Weather
Bureau was transferred into the Department of Commerce, and a river division, known as the NWS
Office of Hydrology, was formed. This river division divided the country into river districts, each
1http://www.idwr.state.id.us/hydrologic/.
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10 Toward a New Advanced Hydrologic Prediction Service (AHPS)
with an associated Weather Bureau office to meet the hydrologic needs of that area. By the end of
World War II, the expanded responsibilities of the regular Weather Bureau offices prompted
separate River District Offices, which through the 1960s combined into the current 13 River
Forecast Centers (RFC2; Figure 1-1). Today, many governmental and non-governmental
organizations share the responsibility of providing hydrologic services in the United States in the
collection and management of hydrologic data and information. AHPS operates as a part of this
hydrologic services enterprise.
ADVANCED HYDROLOGIC PREDICTION SERVICE
The NWS has the primary responsibility among the federal agencies to provide advanced
alerts via flood warnings and forecasts in the United States. Because hydrologic services generate
nearly $2 billion of benefits each year (NHWC, 2002) through timely flood and weather forecasting,
the NWS has made hydrologic understanding and forecasting a priority at national and regional
scales. The NWS Hydrologic Services Division develops hydrologic services for use in accurate,
timely, and useful forecasts with respect to many aspects of the hydrologic cycle. The AHPS
program is a primary vehicle for this mission and has set out seven goals to fulfill it (see Box 1-1).
FIGURE 1-1 Map showing RFC regions.
SOURCE: http://www.weather.gov/ahps/rfc/rfc.php.
2http://aprfc.arh.noaa.gov/resources/docs/apmission.html .
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Introduction 11
BOX 1-1
Goals of the Advanced Hydrologic Prediction Service
· Produce more accurate products incorporating advanced hydrologic science into NWS models
· Provide more specific and timely information on fast-rising floods with increased lead time
· Create new formats, including graphics, for products that are easier to use
· Create more information that is useful to assess risk to flooding, including forecast probability
· Provide products with forecast horizons two weeks or further into the future
· Increase the distribution of products using advanced information technologies (such as the
internet and web-based geographic information system (GIS) formats) to provide broader and
more timely access and delivery of information
· Expand outreach and engage partners and customers in all aspects of hydrologic product
improvement
SOURCE: NWS, 2002.
The NWS began to implement AHPS technologies in the 1980s. At that time, the program
was known as the Water Resources Forecasting System (WARFS). The first prototype of these
technologies occurred in 1997 for the Des Moines River Basin in Des Moines, Iowa. Following this
implementation, AHPS first appeared in the President's Budget Request to Congress for fiscal year
(FY) 1999, and Congress first approved funding for AHPS at $1 million for FY2000.
Congressionally approved funding increased to $6 million in FY2003. In FY2004 and FY2005,
AHPS had more than 1,300 forecast points, and the designated $6 million annual budgets had
portions redirected which resulted in effective budgeting decreases.
Through AHPS, the NWS seeks to provide accurate forecasts that can support timely
warnings for all users of hydrologic forecasts. Throughout history there are numerous examples of
the important role that accurate, effectively communicated warnings play in keeping people and
property safe from water-related disasters. A hydrologic forecast that is accurate, timely, and
relevant is most useful when it elicits a response that leads to an effective action (NWS, 1982). Two
examples demonstrate this connection and application to AHPS.
First, Hurricane Katrina (August, 2005) has brought much attention to the almost
unimaginable destructive power of weather systems and flooding, in particular, as a leading cause of
loss of life and property. With sustained winds during landfall of 125 mph (a strong category 3
hurricane on the Saffir-Simpson scale), Katrina caused widespread devastation along the central Gulf
Coast states of the U.S. New Orleans, LA, Mobile, AL, and Gulfport, MS bore the brunt of
Katrina's force. The National Hurricane Center provided accurate track forecasts and predicted that
Katrina would be a major hurricane 56 hours before landfall. According to emergency management
estimates, 80 percent of the total population of New Orleans evacuated the city before Katrina;
likely 83 percent of the residents of Jefferson Parish, LA, were evacuated (Pedro Restrepo, NWS,
personal communivation, 2006).
However, extreme flooding events caused by Katrina illustrate the need for a hydrologic
prediction system, such as AHPS, to work with an emergency response plan for probable or
imminent flooding. Warnings and response must be much more closely aligned to realize the
benefits of accurate, timely hydrometeorological forecasts. Flooding is often a major problem and
concern associated with hurricanes, and Katrina displays the need for merged advanced storm
surge/coastal water level models and stream flow modeling to improve flood level predictions
during hurricanes and tropical storms. An advanced hydrologic prediction capability could provide
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12 Toward a New Advanced Hydrologic Prediction Service (AHPS)
timely and accurate flood stage forecasts for coastal and inland rivers, which, as Katrina shows, can
be critical in the path a hurricane. A system like AHPS, when fully developed, could also support
retrospective and scenario analyses and generation of flood inundation maps.
The second example is related to the 1997 El Nino year in the southwestern United States.
Statistically, winter precipitation in the Southwest increases during an El Niņo year. In fact, during
the strong El Niņo event of 1997, approximately a 55 percent increase in precipitation (Gelt et al.,
1999) was observed over the Southwest, due in part to Hurricane Nora in September. The short-
term forecasts developed within 24 hours prior to Nora's arrival predicted the path of the hurricane
moving between Tucson and Phoenix, toward the eastern portion of the White Mountains of
Arizona. Four to five inches of precipitation in a 24-hour period were predicted. This amount of
rain would have had a profound impact on the management of the Salt River's reservoir system,
upstream from the Phoenix metropolitan area (Sorooshian et al., 2002). Despite this meteorological
prediction, operators of the largest reservoir on the system, the Roosevelt Dam, followed their usual
operating guidelines and did not release any major amount of water in preparation for the incoming
storm's precipitation and runoff. It is not clear whether hydrologic predictions were made available or
used for this event. In the end, the meteorological forecast was inaccurate, and the hurricane's
actual path deviated 200 miles to the west of its predicted path. Only a trace of rainfall fell in the
Salt River watershed. In hindsight, the reservoir operators made the correct decision, but for the
wrong reason. If the forecasted hurricane path had been correct, then major flooding downstream
of the reservoir, including the greater Phoenix area, would have occurred and the reservoir
operators' decision would have made them responsible for the ensuing losses and damages.
This example illustrates the need for an improved end-to-end hydrologic forecast system.
Such a system would facilitate accurate and accessible hydrologic forecasts, reliable delivery of the
forecasts to decision-makers, and appropriate responses to the hydrologic forecasts. A hydrologic
prediction system, such as AHPS, can provide decision-makers with probabilistic estimates of
potential runoff, which would allow them to formulate responses within a scientifically established
framework. Without such a framework, the full potential and benefit of hydrologic predictions may
not be realized. The reliability and accuracy of hydrometeorological forecasts are expected to
improve over time; decision-makers will learn to use hydrologic information, or ignore it at their
own peril. The operators of the Roosevelt Dam may not be as lucky the next time.
These examples illustrate how prediction and response together make hydrologic predictions
valuable. AHPS, as described by the NWS, strives to provide the information needed at the right
time to facilitate adequate response to mitigate damages to life, livelihoods, and property. This
provision would include predictions from the climate-scale to short-term weather-scale events with
the appropriate representation of uncertainties so that AHPS users can respond to the information
presented to them the best ways possible.
THE NATIONAL RESEARCH COUNCIL STUDY
AHPS is slated to be fully implemented nationwide in 2013. With seven years still remaining
in its development and implementation timeline, a review of the program now is timely and poised
to provide the NWS with information it needs to make AHPS the most useful it can be. In an effort
to help realize the vision for AHPS, the NWS requested a National Academies review of the AHPS
program in the summer of 2003. That fall, the National Research Council's (NRC) Water Science
and Technology Board appointed a committee to assess the full scope of the AHPS program,
including aspects that relate to the nation's needs for operational flood and drought forecasting,
research components of AHPS, and communication and coordination activities associated with
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Introduction 13
flood and drought warning. The committee conducted its deliberations and its report production in
response to the task statement listed in Box 1-2. This report fulfills its charge to review the
scientific, technical, and programmatic aspects of the AHPS program.
Basis for Evaluating AHPS
The NWS provided the NRC committee with documents, oral presentations, and web-
access to relevant AHPS information. These sources of information were used by the committee as
primary descriptors of the AHPS program and formed the basis of the program evaluation. The
AHPS program is described best in and evaluated against the following NWS source documents
which were provided to the committee by NWS' Office of Hydrologic Development:
· NWS. 2001. Implementation of Advanced Hydrologic Prediction Service
· NWS. 2002. Advanced Hydrologic Prediction Service Concept of Services and Operations
· NWS. 2004. Draft: Advanced Hydrologic Prediction Service (AHPS) Development and Implementation
Plan
To supplement information in these source documents, the committee conducted interviews
across the country with internal and external AHPS users. These interviews were used to determine
how well the AHPS mission is being communicated, how a national program is being received and
implemented through local channels, and how well AHPS efforts are coordinated and incorporated
into or affect changes in local operations. Together, the NWS program descriptions and the site
interviews formed the information foundations from which the committee conducted its evaluation
of AHPS. A major challenge that the committee encountered in evaluating AHPS, which is also
BOX 1-2
Statement of Task
The study will review the new program of NOAA's National Weather Service, known as the
"Advanced Hydrologic Prediction Service" (AHPS). The study will assess the full scope of the
program, aimed at improving the nation's river forecasts, in respect to hydrologic science and
technology research, river routing and mechanics, "systems" engineering aspects, and
implementation. Specifically, the study will assess and make recommendations in respect to:
1. the nation's needs in respect to operational flood and drought forecasting and the overall
strategy of AHPS to meet these needs, with emphasis on promoting advances in climate and
weather forecast and the application of modern hydrology, hydraulics, and modeling techniques
and technologies to enhance predictions;
2. assessment of research aspects of AHPS, priorities for science and technology, and means to
facilitate application of research results into hydrologic operations;
3. opportunities to assure optimal communication of warnings and other information generated by
AHPS, including potential new uses of information provided; and
4. the level of coordination with other agencies and entities engaged in flood and drought warning.
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14 Toward a New Advanced Hydrologic Prediction Service (AHPS)
reflected in this report's recommendations, was the surprisingly sparse written or reviewed record of
AHPS models, products, developments, or implementation plans or progress. Therefore, much of
the information used as the basis for evaluating AHPS stems from personal communication with the
NWS and other researchers familiar with AHPS development.
The reliance on personal communication, website information, and power point
presentations provided very little structure against which specific, targeted metrics of assessment
could be developed for and applied to evaluate AHPS. Instead, the committee used the stated goals
of the AHPS program to provide a framework for the program's evaluation and commented on how
the current modeling system, products, approaches, and developments are poised to fulfill AHPS
stated goals. The report's recommendations were aligned with the program's goals to help the NWS
make progress towards achieving them (listed in Box 1-1).
This committee was charged to evaluate the "full scope" of the AHPS program (Box 1-2).
The committee interpreted that charge to include programmatic, scientific, technical, and user-
related aspects of AHPS. Programmatic elements are evaluated against components needed to
support a national program, such as description and statement of program goals, plans for
development, measurable criteria for implementation, and commensurate fiscal and human
resources. Scientific and technical aspects are evaluated against the state-of-the-science research and
ways of incorporating modeling and technical upgrades to the current NWS hydrologic forecasting
operations. User-related issues of AHPS are discussed in terms of current users, their needs, and
how best to address their needs, as well as users expected to access AHPS products in the future,
and how best to use resources for them. For the purposes of this review, the seven AHPS goals are
grouped among programmatic, scientific and technical, and user-related aspects AHPS (Box 1-3).
The Report
The specific charges in the committee's statement of task (Box 1-2) are mapped into this
programmatic, scientific and technical, and user-related framework. Chapter 2 discusses and
evaluates the programmatic aspects of AHPS; it focuses on AHPS implementation and
development, budget, and federal/non-federal coordination and cooperation of hydrologic services.
The AHPS program goal of expanding outreach and partnerships and coordination and cooperation
with other agencies (statement of task item 4), are addressed in Chapter 2. The bulk of the
statement of task charges, and thus the major emphasis of this report, relate to scientific and
technical aspects of AHPS, which are presented in Chapter 3. Chapter 3 evaluates progress and
approaches towards AHPS goals of (1) producing more accurate products, (2) forecasting fast-rising floods, (3)
assessing risk of flooding, and (4) long-term forecast horizons. These goals are evaluated based on current
descriptions of AHPS models, plans for model development, and needs for these types of
hydrologic services. Statement of task items numbers 1 and 2 are addressed in Chapter 3.
Finally, the user-related AHPS goals are evaluated in Chapter 4 in discussions of development and
distribution of graphics and formats of AHPS information and products; ways to identify and
deliver products to a varied user base; and opportunities to assure optimal communication of
warnings and other information (statement of task item 3).
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Introduction 15
BOX 1-3
Categories of AHPS Goals
Programmatic Goals of AHPS
· Expand outreach and engage partners and customers in all aspects of hydrologic product
improvement
Scientific and Technical Goals of AHPS
· Produce more accurate products incorporating advanced hydrologic science into NWS
models
· Provide more specific and timely information on fast-rising floods with increased lead time
· Provide products with forecast horizons two weeks or further into the future
· Create more information that is useful to assess risk to flooding, including forecast
probability
User-Related Goals of AHPS
· Create new formats, including graphics, for products that are easier to use
· Increase the distribution of products using advanced information technologies (such as the
internet and web-based GIS formats) to provide broader and more timely access and
delivery of information
REFERENCES
Gelt, J., J. Henderson, K. Seasholes, B. Tellman, and G. Woodard. 1999. Water in the Tucson
Area: Seeking Sustainability: A Status Report Prepared by the Water Resources Research
Center, College of Agriculture, University of Arizona. Available on-line at
http://ag.arizona.edu/AZWATER/sustainability/ report_html/index.html. Accessed January 19,
2006.
Institute for Business and Home Safety. 2001. Subcommittee on Natural Disaster Reduction.
Lessons from Living with Earth's Extremes. Washington, DC: Institute for Business and
Home Safety.
NHWC (National Hydrologic Warning Council). 2002. Use and Benefits of the National Weather
Service River and Flood Forecasts. Available on-line at http://www.nws.noaa.gov/oh/aAHPS/
AHPS%20Benefits.pdf. Accessed May 25, 2005.
NOAA (National Oceanic and Atmospheric Administration). 2001. Weather Impact on USA
Economy. NOAA Weather Magazine. Online. Available on-line at
http://www.noaanews.noaa.gov/magazine/stories/mag4.htm. Accessed April 13, 2004.
NWS (National Weather Service). 1982. Program Development Plan for Improving Hydrologic
Service. Silver Spring, MD: NWS.
NWS. 2001. Implementation of Advanced Hydrologic Prediction Service. Silver Spring, MD:
NWS.
NWS. 2002. Advanced Hydrologic Prediction Service Concept of Services and Operations. Silver
Spring, MD: NWS.
NWS. 2004. Draft: Advanced Hydrologic Prediction Service (AHPS) Development and
Implementation Plan. Silver Spring, MD: NWS.
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16 Toward a New Advanced Hydrologic Prediction Service (AHPS)
Rayner, S., D. Lach, H. Ingram, and M. Houck. 1998. Weather Forecasts are for Wimps: Why
Water Resource Managers Don't Use Weather Forecasts. Available on-line at
http://www.ogp.noaa.gov/mpe/csi/econhd/1998/rayner_final.pdf. Accessed August 4, 2005.
Sorooshian, S., M. Whitaker, and T. Hogue. 2002. Regional and global hydrology and water
resource issues: The role of international and national programs. Aquatic Sciences 64: 317-
27.
Stallings, E. 1997. The Benefits of Hydrologic Forecasting. Silver Spring, MD: NOAA.
USACE (U.S. Army Corps of Engineers). 2000. Annual Flood Damage Report to Congress for
Fiscal Year 2000. Washington, DC: USACE.
Representative terms from entire chapter:
advanced hydrologic
