Land Use and Climate.

Terrestrial ecosystems affect climate through exchanges of energy, water, momentum, mineral aerosols, CO2, and other atmospheric gases. Changes in community composition and ecosystem structure alter these exchanges and in doing so alter surface energy fluxes, the hydrologic cycle, and biogeochemical cycles. As a result, changes in land cover through natural vegetation dynamics or human uses of land can alter climate. Much of our knowledge of the influence of vegetation on global and regional climate comes from climate models. In these models, the absorption of radiation at the surface, the exchanges of sensible and latent heat between land and atmosphere, storage of heat in soil, and the frictional drag of the surface on wind influence climate. Important surface properties that determine these exchanges include: albedo, which determines the absorption of solar radiation at the surface; surface roughness, which affects turbulence and the turbulent fluxes of sensible heat, latent heat, and momentum; soil water, which affects the partitioning of net radiation into sensible and latent heat; vegetation, which alters the hydrologic cycle and also affects albedo, surface roughness, canopy physiology, and the leaf area from which heat and moisture are exchanged with the atmosphere; and soil texture, which affects infiltration, runoff, and soil water. The first generation of land models coupled to atmospheric models parameterized these processes using simple aerodynamic bulk transfer equations and simple prescriptions of albedo, surface roughness, and soil water (Sellers et al., 1997). These models evolved into a second generation of models such as the Biosphere-Atmosphere Transfer Scheme (BATS, Dickinson et al., 1993) or Simple Biosphere Model (SiB, Sellers et al., 1986) that include the full hydrologic cycle and vegetation effects on energy and water fluxes. [ABSTRACT FROM AUTHOR]