Research Strategies for the U.S. Global Change Research Program (1990) / Chapter Skim
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5 Water-Energy-Vegetation Interactions
5 Water-Energy-Vegetation Interactions
Pages 131-163
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From page 131... ...
This chapter focuses on the interactions between the vegetated land surface and the atmosphere, particularly on the exchanges of energy, water, sensible heat, and carbon dioxide between the two. The aim of the research strategy discussed here Is not merely to describe such exchanges but to fully understand them so that predictive modeling can be used to explore possible future states of the earth system.
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From page 132... ...
Additionally, the data are to be used for monitoring the global environment and testing new hypotheses and for diagnostic or retrospective studies. · To conduct manipulative experiments, field campaigns, and process studies to improve our understanding of the processes controlling the transfer of energy, water, heat, and carbon dioxide between the land surface and the atmosphere at appropriate scales and to develop better methods for quantifying the controls.
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From page 133... ...
. The sections on data needs and modeling follow the structure outlined in Figure 5.1 by first reviewing global data set needs and then reviewing data needs at progressively finer spatial and temporal scales.
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From page 134... ...
GIMMS; National NASA, NOAA Environmental Satellite, Data, and Information Service; and other national programs Retrospective land cover IRAP/Intemational Satellite NASA studies Land Surface Climatology Project Soil moisture, vegetation Goddard Space Flight Center NASA cover Snow and ice Goddard Space Flight Center NASA, NOAA Runoff ? WCRP Carbon dioxide Background Air Pollution NOAA Monitoring Network TABLE 5.2 Manipulation Experiments/Gradient Studies (Ongoing)
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2 Energy balance, 1987, 1989 FIFE Kansas, USA NASA biophysics, 1988 on KUREX Kursk, USSR USSR meteorology, remote sensing (15 km) 2 TABLE 5.3b Field Campaigns (Planned)
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From page 136... ...
Global Data Needs Global data are needed for the specification of boundary conditions for global models as well as for the framework for analyzing and detecting global change. The data would come from extensive ground and aircraft surveys as well as from satellites.
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From page 137... ...
The resolution of available global data sets for the land surface is either 5 or 10 minutes, depending on the continent. Present data are inadequate for many land surface studies.
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The temporal and spatial variations of soil moisture are not well known. In most models, the soil-water-holding capacity associated with different vegetation types is specified, but there is no observed climatology of the field capacity.
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From page 139... ...
Long-Term Monitoring A global network of minimally instrumented sites is needed to provide data for diagnosing the effects of climatic change over long periods of time, · testing basic models and hypotheses, and · anchor stations to perform satellite algorithm inversion. The first objective, diagnosing the effects of climatic change, will require different measurement strategies in different parts of the world.
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From page 140... ...
At minimum, these sites should be committed to collecting meteorological data and conducting periodic surveys of the vegetation and soils in their locale. Integrated Monitoring and Process Studies Out of the larger set of long-term monitoring sites, a few (fewer than one hundred worldwide)
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From page 141... ...
, ecosystem structure and productivity, land use and soil information, atmospheric optical depth, large-area surface fluxes (tower) , trace gas concentrations, and occasionally fluxes, and selected satellite data.
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From page 142... ...
watershed approach may be also be valuable for lumped soil moisture modeling studies, which can be integrated with remote-sensing-based procedures for estimating this variable. Particular attention needs to be given to procedures for making largescale estimates of soil moisture in a timely and cost-effective manner.
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From page 143... ...
need to be improved. The NCAR Atmosphere-Surface Turbulent Exchange Research (ASTER)
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From page 144... ...
Integrated Ecosystem Experiments Integrated ecosystem experiments, manipulations that expose whole ecosystems to simulated climatic change or components of climatic change, will be critical for two reasons. First, they will provide the most concrete and complete evidence of the response of ecosystems to climatic change, and they can potentially provide it in a way that facilitates quantification of the mechanisms driving the responses.
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· Ecosystem sensitivity. Process studies and historical observation have identified several ecosystems likely to be greatly affected by or especially sensitive to climatic change (e.g., coastal marshes and arctic tundra, respectively)
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Field experiments should be sited within longterm monitoring sites, and measurement should be integrated with the longterm effort as far as possible. · Theoretical framework.
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Areas where there are large-scale ongoing impacts, e.g., the Amazon tropical forest, should have a high priority for combined long-term process studies and field campaign investigations. Such studies should address changes in surface energy and water balance, soil hydrological processes, soil physics and chemistry, species succession, and dynamics (socioeconomic)
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. Fundamental Research and Laboratory Work Fundamental research needs to be supported in a number of key areas, including remote sensing techniques, detailed ecological and hydrological process studies, and the development of improved measurement techniques.
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The challenge of developing ecosystem models competent to predict ecosystem responses to climatic change has several aspects that need to be supported with process studies. Some of these process studies (e.g., species change)
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The interface between the indications of interspecific generality and species individuality is a critical area to resolve, both because of the potential simplification that results from a species-independent perspective and because the ecosystem consequences of species change are central components of ecosystem responses to climatic change. · Community ecology.
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· Population biology. Ecosystem responses to global change will almost certainly result from the combined effects of (1)
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From page 152... ...
\Module I Seconds Days Years Centuries Ecosystem Dynamics | I Models l Time ~ FIGURE 5.3 Relationships between land surface parameterizations, atmospheric general circulation models, and ecosystem dynamics models show disparity in time and space scales. For more effective global change research, two new "communication" techniques or "modules" must be developed to interpret results between model classes.
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From page 153... ...
. Essentially, the LSPs assume a static ecosystem structure and a prescribed phonology, which in turn define the albedo and roughness length characteristics of a given area and the evapotranspiration response as a function of soil moisture.
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(c) Ecological change in species composition results in changes in land surface characteristics of albedo, roughness, and soil moisture availability with possible feedbacks on near-surface climatology.
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However, before significant progress can be made in the area of medium- to long-term atmosphere-biosphere interactions, it will be necessary to construct more rigorous linkages between the LSP-GCMs and EDMs. It is proposed that this be done by constructing "forcing modules," to convert GCM output into "forcing" climatologies for EDMs, and "aggregation modules" to aggregate the effects of ecosystem dynamics changes into representative LSP parameter sets.
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From page 156... ...
In particular, the following physiological phenomena should be described as functions of GCM prognostic variables (temperature, humidity, soil moisture, radiation, and so on) : time series of green leaf area index; rooting depth; and roughness length, albedo, photosynthetic capacity, and maximum canopy conductance if these are not functions of leaf area index and rooting depth.
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Ecosystem Structure Models The models discussed in previous sections can describe the effects of changes in land surface biophysical parameters (e.g., albedo, roughness, and moisture availability) and biogeochemical properties (e.g., nutrient cycling rates)
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It is strongly recommended that research efforts be encouraged on a broad front: the preliminary biogeographical models will provide us with the means to explore the possible sensitivity of land-surface- atmosphere interactions to changes in surface conditions. This approach is represented by Loop I in Figure 5.5, where a climatic change scenario leads to a simple definition of a new (steady state)
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Output to ecosystem function models FIGURE 5.5 Proposed approach for modeling vegetation (ecosystem) charge subject to large changes in forcing functions.
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For example, if analyses indicate that GCM-simulated climates for continental interiors are sensitive to the successional stage of the vegetation cover there, it would be highly desirable to increase the flow of resources for improving the ecosystem dynamics models, which could then provide more realistic boundary conditions for the GCM. For this and similar problems, a gradualist approach to the sensitivity problem should be used.
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From page 161... ...
Summary The above analysis has called out the need to vigorously promote research efforts in a few areas of obvious weakness. However, it should be reemphasized Hat modeling efforts in all the relevant areas should be supported to a much greater extent than they are now; these include the ecosystem dynamics models, land surface parameterizations, and atmospheric general circulation models.
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From page 162... ...
To address the goals of ensuring a continuous, high-quality monitoring effort while suitable for intensive field experiments of the scale of FIFE or larger, there should be permanent research staff attached to each center. These staff, in cooperation with visiting scientists, should also carry out an educative and training function.
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1982. Land Surface Processes in Atmospheric General Circulation Models.
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