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<br />20 <br /> <br />o <br />"l <br />C;, <br />I-" <br /> <br />U = (tp/lOO) (ktkcl (12) (A)...................... (4) <br /> <br />where U is the consumptive use of the crop in acre-feet, t is mean <br /> <br />temperature in degrees Fahrenheit, p is the yearly percentage of <br /> <br />daylight hours occurring during the time period under consideration, <br /> <br />kt is a climatic coefficient expressed as; <br /> <br />kt = O. 0173 t - O. 314. . . . . . . . . . . . . . . . . . . . . . . . . . . (5) <br /> <br />kc is the crop growth stage coefficient determined experimentally, <br /> <br />and A is the acreage of land use in the area. <br /> <br />Jensen-Haise method <br /> <br />The Jensen-Haise method was formulated from the reevaluation <br /> <br />of about 3,000 published and unpublished reports on short period <br /> <br />measurements of evapotranspiration using soil sampling procedures <br /> <br />during a 35-year interval in the western USA. (7) The resulting <br /> <br />equation is expressed as, <br /> <br />ET = Kc Etp. . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . .(6) <br /> <br />where ET is the evapotranspiration, Kc is a crop coefficient much like <br /> <br />the Blaney-Criddle kc val\le, Etp is the potential evapotranspiration <br /> <br />in a well watered soil in a semiarid area. The value of Etp is com- <br /> <br />puted by a relationship between air temperature and solar radiation, <br /> <br />Etp = (0. 014t - 0.37) Rs... ........ ............ (7) <br /> <br />where t is the temperature in degrees Fahrenheit, and Rs is the solar <br /> <br />radiation in Langleys. <br /> <br />.i ~ <br /> <br />, <br />i:i1;..~~ <br />