Water serves as the primary conduit of energy transfer in the overall earth system.
Variations and long- term changes in climate are both the result of and result in changes in the ways water is integrated by geological, biological and atmospheric systems. 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.