The surface of the earth is the gateway for energy (heat), moisture, and trace gases to enter or leave the atmosphere. It also is where kinetic energy of mass motion is extracted from the atmosphere. Global and regional climate models require accurate information on the rates of input of heat and moisture and extraction of momentum (kinetic energy). An amount per unit time of some quantity (heat, mass, momentum, etc) passing through a surface is known as a flux. Soil-vegetation-atmosphere transfer models (SVATs) are used to link to global and regional climate models to more accurately describe how soil, vegetation, and water surfaces exchange fluxes with the atmosphere.