Regional Estimates of Evapotranspiration

Estimates of regional evapotranspiration (ET) are necessary inputs to world climate models, regional water use and supply planning and assessment, estimates of potential food production capacities and supplies, and hydrologic studies. The chapter cites methods for determining ET at specific locations that are regionally valid when applied with gridded or spatially representative data. The most readily used methods for regional application are the water balance method, lysimeters, energy balance methods, and mass transfer or modeling methods. The chapter describes applications of the complementary approach and energy balance models for regional estimates of ET from forests, grasslands, and agricultural areas. It also describes data sources to support regional ET estimates, including gridded weather data. Satellite imagery combined with surface climate measurements has been used to estimate ET from large-scale cultivated lands and determine the productivity of water in these areas.