Abstract

Despite the significance of water, our knowledge of it as part of the global, interacting system is meager. Consequently, we are far from understanding how the hydrologic cycle will respond to a changing Earth system, or the nature of water's influence across the components of the system. To address these issues, the primary research strategy of this investigation, centers on nesting or coupling coarse resolution GCMs, with high resolution mesoscale models, with models including soil moisture, vegetation, and surface and groundwater hydrology. In this manner, we are attempting to produce global change predictions, in response to a variety of factors ranging from increases in greenhouse gas concentrations to changes in land cover, at a spatial scale which is appropriate to assess their impact. This research strategy is accomplished through an emphasis on integrated regional studies and the development of coupled earth system models. A basic requirement to accomplish these goals is also to develop data sets for initialization and validation of the various models at a variety of spatial scales, and to focus on critical limitations in current models (e.g. cloud parameterizations). During this process, we also contribute to the production of data sets which describe changes in climate and the nature of climate variability.

Background

The critical facets of climate and hydrology research needs have been described in NRC reports (e.g. 1985), in planning documents of the USGCRP and the WCRP (e.g. CLIVAR and GEWEX), and in "Earth System Science: A program for global change." The primary research objectives are clear: determine and understand the dynamics of the major reservoirs of water, the mechanisms for transfers of water between global reservoirs, predict changes in the distributions, volumes, fluxes of water resulting from change and from human activities, and understand better the coupling of water with other components of the Earth system.

We proposed to develop methodology and modeling capabilities to describe quantitatively the presently uncertain rates associated with the sources, sinks, and fluxes of the global water cycle with the ultimate goal of increasing our ability to predict changes in the hydrologic cycle associated with natural variability and human activities. A key element is to address changes in the hydrologic cycle at a scale appropriate for considering its impact on human activities, including agriculture and water resources. The proposed research included 31 specific objectives, which are summarized here, for the sake of brevity, as 12 primary objectives:
  1. Evaluate GCM capability to simulate hydrologic cycle components
  2. Evaluate GCM sensitivity to lower boundary forcing
  3. Generate global data sets for documentation of global change, specifically for hydrologic variables, and for global model validation and verification
  4. Develop improved treatment of cloud and precipitation processes
  5. Develop and test components of high resolution regional atmospheric models critical for water and energy fluxes
  6. Test the adaptability of terrestrial hydrologic models for sensitivity to spatial and topographic scales
  7. Develop and test indirect measures of soil water content, with the objective of integrating these results into mesoscale model simulations
  8. Develop and test coupled (nested) GCM-Mesoscale-Hydrologic Forecast models
  9. Develop comprehensive databases and GIS for regions, such as the Susquehanna River Basin, the Cape Region, and others, to facilitate the development and evaluation of the nested model approach to regional prediction.
  10. Determine ice sheet mass balance, linking climate and hydrologic changes to the future evolution of the cryosphere
  11. Develop and test a landscape evolution model in order to link climate and hydrologic changes to the evolution of the land surface
  12. Develop improved climate-agriculture models in order to link climate and hydrologic changes to the human dimensions of global change
These objectives incorporate three major integrating elements: (1) Documentation of Earth system change (4-dimensional multiphase water, temperature and diabatic heating, ice sheet mass balance, and regional scale terrestrial and atmospheric water and energy budgets), (2) focused studies on controlling processes (cloud processes, the interface of the atmosphere with ocean, cryosphere, biosphere and land surface), and (3) integrated conceptual and predictive models (extension of predictive capability across a spectrum of spatial scales, verification and validation of hydrologic cycle predictive capability, and coupled Earth system models).
The objectives and the integrating elements include a large number of challenging scientific issues requiring focused research and the interactions of a significant number of disciplines. Such a comprehensive set of objectives presents challenges for even a large team of investigators. As a practical element, the significant advances of this project are occurring because of the development of regional-scale "experiments" designed to improve understanding of important physical processes, develop coupled models, and assess and validate model predictions. Almost the entire research team contributes to these regional-scale experiments, each cooperatively seeking to advance the research objectives outlined above.

To date, much of the emphasis of the project has focused on the Susquehanna River Basin, with additional research on the Cape region of Florida. Much of the future work is proposed for the Ohio and Tennessee River Basins. These regions have been the focal point for assessing GCM capability, coupling and evaluating GCMs with mesoscale models, incorporating improved surface processes within the mesoscale models, integrating soil moisture measurements and models, evaluating and linking terrestrial hydrologic models of surface flow and groundwater, developing comprehensive GIS with a full spectrum of data for specification of model boundary conditions and evaluating predictions, and linking these models with other elements of the Earth system (e.g. landscape evolution) and societally-important issues (e.g. impacts of changes in the hydrologic cycle on agriculture).

The primary research strategy of this investigation, therefore, centers on nesting or coupling coarse resolution GCMs, with high resolution mesoscale models, with models including soil moisture, vegetation, and surface and groundwater hydrology. In this manner, we are attempting to produce global change predictions, in response to a variety of factors ranging from increases in greenhouse gas concentrations to changes in land cover, at a spatial scale which is appropriate to assess their impact. Such a strategy introduces the potential that we will link the errors of one model with the errors of each of the nested models. However, we have not jumped to make regional global change predictions. Rather, our efforts are directed to a series of careful studies designed to improve understanding and assess model capability critically. The completed and planned studies of this investigation are not only describing the uncertainties, but are, perhaps more importantly, substantially increasing our knowledge of a variety of processes, and providing a strong foundation for high resolution, coupled Earth system models. We are establishing a greater capability to utilize EOS observations to describe key hydrologic and climatic processes, to further develop and validate models, increasing our understanding of the past and the future and their relationships to Earth system components and thus providing a more robust predictive capability.

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Comments to: R. White, raw@essc.psu.edu