Evapotranspiration on the Watershed Scale Using the SEBAL Model and Landsat Images

Abstract

SEBAL (Surface Energy Balance Algorithm for Land) is an image-processing model comprised oftwenty-five submodels that calculates evapotranspiration (ET) and other energy exchanges at the earths surface.SEBAL uses image data from Landsat or other satellites measuring thermal infrared radiation, visible and near-infrared.SEBAL was developed in the Netherlands by Bastiaanssen and was modified during this study formountainous terrain and clear, cold lakes. ET is computed on a pixel-by-pixel basis from an energy balance.The Bear River Basin covers 20,000 km 2 of Idaho, Utah, and Wyoming and contains about 190,000 ha of cropland. ET maps were generated on a monthly basis. The maps show a progression of ET during the year as well asdistribution in space. Predicted ET was compared with lysimeter measurements of ET with good results, withmonthly differences averaging +/- 16%, but with seasonal differences of only 4% due to reduction in random error.