Near-Real-Time Evapotranspiration Tools in the Upper Klamath Basin

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The USGS, in cooperation with the Bureau of Reclamation, has developed a near-real-time method for determining provisional evapotranspiration (ET) in the Upper Klamath Basin of Oregon and California. Because evaporation uses heat energy, ground surfaces with large ET rates are left cooler than ground surfaces that have less ET. As a consequence, irrigated fields are distinguishable from nonirrigated fields on thermal imagery captured by Landsat satellite data. These data are processed by a contractor (Evapotranspiration, Plus, LLC) to create fraction of reference evapotranspiration (ETrF) maps. For each mostly cloud-free Landsat image, ETrF maps are created using part of the METRIC algorithm (Mapping EvapoTranspiration at High Resolution and Internalized Calibration, Monthly 30-m  provisional ET maps are then calculated by calibrating the satellite-based ETrF using alfalfa reference evapotranspiration from ground-based Bureau of Reclamation Agrimet stations. Near-real-time ET from this method that uses part of the METRIC algorithm was compared with ET calculated from the full METRIC algorithm using regression analyses, producing an R2greater than 0.99. 

Author Name
Jonathan Haynes
Author Email