An evaporation estimation method based on the coupled 2-D turbulent heat and vapor transport equations

The analytical solution of the coupled turbulent diffusion equations of heat and vapor transport across a moisture discontinuity under near-neutral atmospheric conditions and constant energy available at the evaporating surface yields a simple equation (i.e., the wet-surface equation [WSE]) that relates the change in surface temperature to the change in the land surface moisture content as the environment dries. With the help of percent possible sunshine, air temperature, and humidity measurements at selected weather stations as well as land surface temperature values from MODIS data, monthly, warm-season evaporation rates were estimated for five rectangular regions across the contiguous U.S. employing the WSE. The so-derived monthly evaporation rates correlated very strongly (R2 = 0.95) with traditional complementary relationship-derived evaporation estimates using the same weather-station data. Even on an annual basis the correlation remained unchanged. WSE with no tunable parameters may in the future help in calibration and validation of other evaporation estimation techniques that may or may not rely on land surface temperature data