SATELLITE-BASED EVAPOTRANSPIRATION BY METRIC AND LANDSAT FOR WESTERN STATES WATER MANAGEMENT

Abstract

Abstract METRIC TM (Mapping Evapotranspiration at high Resolution and with Internalized Calibration) is an image-processing model comprised of multiple submodels for calculating evapotranspiration (ET) as a residual of the surface energy balance. METRIC is a variant of SEBAL, an energy balance process developed in the Netherlands by Bastiaanssen. METRIC was extended for application to mountainous terrain and to provide tighter integration with ground-based reference evapotranspiration. METRIC has been applied with Landsat images in southern Idaho, southern California, and New Mexico to predict monthly and seasonal ET for water rights accounting and for operation of ground water models. ET “maps” (i.e., images) via METRIC provide the means to quantify, in terms of both the amount and spatial distribution, the ET on a field by field basis. The ET images generated by METRIC show a progression of ET during the year as well as distribution in space. Comparisons between ET by METRIC, ET measured by lysimeter and ET predicted using traditional methods have been made on a daily and monthly basis for a variety of crop types and land-uses. The results suggest that METRIC or similar methods hold substantial promise as efficient, accurate, and inexpensive procedures to predict the actual evaporation fluxes from irrigated lands throughout a growing season.