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ESTIMATION OF EVAPOTRANSPIRATION ACROSS THE CONTERMINOUS UNITED STATES USING A REGRESSION WITH CLIMATE AND LAND-COVER DATA <br /> 1r_T <br /> i <br /> -3 <br /> i <br /> e <br /> Lake County <br /> Estimated mean annual actual <br /> evapotranspiration,in centimeters, <br /> during the period 1971-2000 <br /> _0-10 41-50- 81-90 <br /> - 11-20 r" 51-60_ 91-100 <br /> 21-30- 61-70 <br /> 31-40 71-80 <br /> FIGURE 14. Map of Estimated Mean Annual Actual Evapotranspiration(ET)for the Conterminous U.S.for the Period 1971-2000.Estimates <br /> are based on the regression equation of ET/P in Table 1 that includes land cover multiplied by the mean annual precipitation from the <br /> PRISM climate data for the same period.Calculations of ET were made first at the 800-m resolution of the PRISM climate data.The mean <br /> values for the counties(shown)were then calculated by averaging the 800-m values within each county. <br /> watersheds to compile a proxy dataset of observed SUPPORTING INFORMATION <br /> ET. Climate and precipitation data at these same <br /> watersheds were then used as parameters in a <br /> regression equation to create a best fit to the Additional Supporting Information may be found <br /> observed data. The result was a regression equation in the online version of this article: <br /> that can predict ET at any given site based solely Table Sl. Data associated with the 838 water- <br /> on climate, or climate and land-cover, variables sheds used to create the regression equation. <br /> with an R2 value of 0.87 or greater. By then apply- Table S2. Data associated with the 342 large <br /> ing this regression equation to climate and land- watersheds used to test the validity of the regression <br /> cover values for each county across the entire con- equation. <br /> terminous U.S., maps were created for ET and <br /> ET/P for the country. The ET/P map illustrates <br /> that, in certain regions, such as the High Plains LITERATURE CITED <br /> and the Central Valley of California, ET exceeds <br /> precipitation because of the import of water other Allen, R.G., 1997. Self-Calibrating Method for Estimating Solar <br /> than that available from local precipitation. These Radiation From Air Temperature. Journal of Hydrologic Engi- <br /> maps should be useful for regional water managers, neering 2(2):56-67. <br /> and the method useful for application in more Baldocchi,D.,E.Falge,L.Gu,R.Olson,D.Hollinger,S.Running, <br /> P. Anthom, C. Bernhofer, K. Davis, R. Evans,J. Fuentes, A. <br /> detail at the state level or in other regions of Goldstein, G. Katul, B. Law,X. Lee,Y. Malhi,T. Meyers, W. <br /> the world where climate and land-cover data are Munger, W. Oechei, KT. Paw, K Pilegaard, H.P. Schmid, R. <br /> plentiful. Valentini,S.Verma,T.Vesala,K.Wilson,and S.Wofsy,2001. <br /> JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 229 JAWRA <br /> CJK Milling LLC Figure 11-1: Evapotranspiration <br />