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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />2479 Ct was later defined as:!.!.! <br /> <br />Ct ; 1/(Cl + C2 Ch) <br /> <br />where Ch ; 50 mb/(e2-el), <br />C2 ; 7.6 degrees c, <br />and Cl; 38 - (2.0 K elev/305) <br /> <br />e2 and el are the saturation vapor pressures in <br />millibars at the mean maximum and mean minimum <br />temperatures for the warmest month of the year in a <br />given area. <br /> <br />Crop ET is obtained by application of suitable alfalfa based crop <br /> <br />factors. <br /> <br />The equation may be used with or without the elevation correction <br /> <br />(elev. ; 0.0). Caution should be exercised in the use of Ct and TK <br /> <br />with full elevation correction for elevations above 4500 feet ~/. <br /> <br />Evidence exists from field studies which indicate Jensen-Haise may <br /> <br />over predict ET at these elevations. Jensen-Haise may under predict <br /> <br />ET under very windy conditions. <br /> <br />Jensen-Haise equations are frequently modified or calibrated for <br /> <br />specific geographic areas. Two of these locally calibrated <br /> <br />equations are used for comparison in this report. Equation (14) was <br /> <br />developed for use in northeast Utah and provided by Dr. Robert Hill at <br /> <br />Utah State University: <br /> <br />ETo ; 0.009 x T (degrees F) x Rs x 0.000673 (14) <br /> <br />and Equation (15) was developed for the NIIP: <br /> <br />ETo ; 0.15 x [T(degrees F)-14] x RS x 0.000673 (ly) (15) <br /> <br />Equations 14 and 15 provided very similar estimates of reference crop <br /> <br /> <br />ET in the example calculations found later in this section. <br /> <br />1-16 <br />