Characteristics of the surface affect the evolution of water distribution through a variety of processes such as evapotranspiration, surface radiation, energy fluxes, precipitation, and surface and subsurface water flow. Vegetation is one of the principal variables affecting land surface properties, water flux and, ultimately, regional and global hydrologic processes. Of particularly high priority to the overall Global Change Program is reducing uncertainty in climate models which requires a better understanding of the role that clouds play in key climate processes. Energy and water are also intricately woven in governing biogeochemical cycles. The interactions among the atmosphere, earth and biosphere are complex and further complicated by the range in spatial scales at which these interactions occur.
Water plays a central role in the evolution and health of ecosystems and climate processes.
Understanding the physical and biological processes that govern the distribution of water will be essential as input for economic planning and decisions relating to agriculture and forestry, desertification, energy needs, and biodiversity as well as the basis for understanding and eventually modeling and predicting long-term climate and global change.