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Estimating actual evapotranspiration without land use classification




Thoreson, Bryan, author
Zwart, Sander, author
Bastiaanssen, Wim, author
Davids, Grant, author
U.S. Committee on Irrigation and Drainage, publisher

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Water resource planning requires knowledge of consumptive water use by crops and natural vegetation. Remote sensing offers the promise of obtaining consumptive use and other water resource data over large areas at regular intervals. SEBAL (Surface Energy Balance Algorithm for Land) uses data gathered by satellite-based sensors to compute the energy balance at the earth's surface. Evapotranspiration (ET) is predicted as a residual of the energy balance, without needing to know crop or vegetation type, or other ground-based information, except routine weather data. Utilizing SEBAL, annual actual ET in 2002 for the state of California has been computed from MODerate-resolution Imaging Spectroradiometer (MODIS) satellite images for each square kilometer. Annual ET can be summarized spatially using any spatial characteristic for which a GIS overlay is available or can be developed. Annual ET was summarized spatially by land use, county and watersheds. Validation of the SEBAL process is discussed in general and for this specific application. Annual actual ET from a MODIS pixel comprised of largely alfalfa fields was found to differ by 0.9 percent from alfalfa annual actual ET measured by a lysimeter maintained by the United States Department of Agriculture, Agriculture Research Service near Fresno, California (Ayars and Soppe, 2003).


Presented during the USCID water management conference held on October 13-16, 2004 in Salt Lake City, Utah. The theme of the conference was "Water rights and related water supply issues."

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