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<br />. <br /> <br />. ' <br /> <br />OOlH3 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />use. USDA, 1979. reported that ETM070 was developed by the USBR and incorporates <br />a Jensen-Haise equation. <br /> <br />In the past, a major limiting factor in using reference crop type equations was the <br />extensive amount of meteorological data required. The combination equations which <br />include Penman Monteith, 1982 Kimberly Penman and FAO Penman require measured <br />temperature, solar radiation, wind, and vapor pressure or relative humidity. However, <br />several equations, FAO Blaney-Criddle and 1985 Hargreaves require only temperature data. <br />Jensen et al., 1989, found that all of the forenamed equations provide a more accurate <br />estimate of ET than SCS-BC. <br /> <br />Dr. Harold Duke of the USDA Agricultural Research Service has set up the Colorado <br />Agricultural Meteorological Network (COAGMETI. COAGMET provides data for calculating <br />crop water use using a combination (i.e. Penman type) equation. The data is easily <br />~\.""" <br />accessible through Internet. There are six stations located in the Colorado River basin ._ - \,,,,,,,,, ? <br />(Cortez, Dove Creek, Yellow Jacket, Delta, Fruita and OIathe). Most of these stations S\">' <br />were established in 1992. However, the ARS has operated a weather station at Fruita, <br />measuring wind, solar, temperature and etc since the early 1970's. <br /> <br />Allen and Brockway reported on a reference ,crop evapotranspiration, based <br />procedure developed for estimating ET on a statewide basis with mean air temperature <br />serving as the only measured equation variable. In a recent water court proceeding, <br />Wheeler, 1991, described a procedure for estimating Etr using daily values of SCS-BC's <br />tpl1 00 and monthly calibration coefficients. The monthly calibration coefficients were <br />based upon an analysis comparing daily values of tp/1 00 to daily values of Etr calculated <br />using the 1982 Kimberly Penman. Allen reported on calibration of Hargreaves type <br />temperature-difference-extraterrestrial radiation equation using a grass reference Penman <br />Monteith equation. Garcia et al. developed a standard set of evapotranspiration reference <br />maps for the Western Slope of Colorado by combining a Graphical User Interface, a <br />Geographical Information System and weather data, and using a Penman Monteith. <br /> <br />7 <br />