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<br />'." <br /> <br />" <br /> <br />.. <br /> <br />" <br /> <br />2.4 <br /> <br />Estimation of Seasonal Water Reouirement <br />. <br /> <br />The total water use from planting to harvest for a given crop is. <br /> <br />called seasonal water use or seasonal water requirement. When gro~TI <br /> <br />under si~ilar climatic conditions with water not limiting crop production, <br /> <br /> <br />the seasonal water requirement is about the same on all soils. This enables <br /> <br />application of water requirement data from one station to another. <br /> <br />Seasonal water requirements for each crop considered to be grown on the <br /> <br />Towaoc lands were adopted from USBR* estimates. Potential evapotransportation <br /> <br />(ETp) was estimated by the Jensen-Haise Method (Jensen and Haise, 1963). <br /> <br /> <br />'This method is based on energy balance concepts and is the best alternative <br /> <br />when climatic input is incomplete to apply the combination (energy balance <br /> <br />and aerodynamic) method. The Jensen-Haise method was developed from <br /> <br /> <br />. observations in the Western United States. It requires average temperature <br /> <br />and solar radiation as input data. The empirical relationship given by <br /> <br />. <br /> <br />Jensen and Haise is: <br /> <br />ETp .. 0.014 C(T - 26.4) Rs <br /> <br />(2.1) <br /> <br />where ETpo measured"in inches per day, is the potential evapotranspiration from a <br />reference crop that is well-watered. T is average temperature in OF; Rs is short <br />-2 -1 <br />wave sOlar radiation received' by the surface, in langleys per day (Cal cm ,day); <br /> <br />and C is the conversion factor (0.000673) so that ,ET is in 'inches per day. <br />. p. - <br />~ Mean monthly solar radiation measured at Grand Junction, Colorado for- <br /> <br />the period 1952-1973 was adopted by USBR with slight modification (Table 2.1). <br /> <br />The corresponding mean monthly temperatures are adopted from measurements <br /> <br />at Towaoc within the Ute Mountain Ute Indian Reservation (Table 2.2). <br /> <br />* United States Bureau of Reclamation, Durango Branch Office <br /> <br />. <br /> <br />.~ <br />