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<br />. <br /> <br />. <br /> <br />A representative climatic station will be selected for each <br /> <br />subarea. Using historical records of temperature, precipitation, <br /> <br />e:>. <br />c..-) <br />~ <br />.... <br />~ <br /> <br />frost dates, and planting and harvesting dates, a consumptive <br /> <br />use rate will be computed for each major crop in each of the <br /> <br />reporting years. <br /> <br />Irrigation consumptive use rates will be determined by subtrac- <br /> <br />ting the effective precipitation from the consumptive use <br /> <br />rates. Effective precipitation will be computed using criteria <br /> <br />described in the U.S. Department of Agriculture, Agricultural <br /> <br />Research Service, Technical Bulletin No. 1275. (It may be <br /> <br />necessary to modify the effective precipitation criteria for <br /> <br />use in desert regions.) The values of irrigation consumptive <br /> <br />use rates will be applied to the estimates of irrigated acreage <br /> <br />to yield values of irrigation consumptive use. <br /> <br />The above procedure will yield a determination of a theoretical <br /> <br />water requirement if the lands received a full water supply. <br /> <br />However, many irrigated lands in the Upper Colorado River Basin <br /> <br />receive less than a full supply of water, either due to lack of <br /> <br />distribution facilities or inferior water rights. Theoretical <br /> <br />irrigation water use will have to be adjusted on the basis of <br /> <br />previous inventories and histories of short supply lands and on <br /> <br />the basis of streamflow conditions and irrigation records <br /> <br />during the year under study. It may also be possible to <br /> <br />quantify shortages by working with crop yield reports. Identi- <br /> <br />fication of shortages will be particularly important for 1977 <br /> <br />values. <br /> <br />10 <br />