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<br />. <br /> <br />. <br /> <br />. <br /> <br />~01179 <br /> <br />Climatic Data <br /> <br />Climatic data was collected from all weather stations in and around the Upper <br />Colorado River Basin. These were inspected for length of record and <br />applicability to the local irrigated areas. In all, 40 stations were selected <br />for use. To more closely approximate the temperature conditions of the <br />irrigated areas, a monthly temperature increase of 4'F/I,OOO feet decrease in <br />elevation was applied. <br /> <br />Davliaht Percentaaes <br /> <br />The monthly daylight percentage values, which vary according to latitude, were <br />obtained from tables in SCS Technical Release No. 21. Irriaation Water <br />Reauirements, The percentages were linearly adjusted for the partial months <br />falling at the beginning and end of the growing season. <br /> <br />Croo Growth Staae Coefficients <br /> <br />Values for K, a coefficient reflecting the growth stage of a particular crop, <br />were obtained from the curves supplied in SCS Technical Release No. 21. <br />Irriaation Water Reauirements. Crops were placed in 10 categories: alfalfa, <br />pasture grass, spring grain, potatoes, small vegetables, spring wheat, corn, <br />dry beans, orchard without cover, and sugar beets. <br /> <br />Effective Rainfall <br /> <br />Effective rainfall is defined as precipitation occurring during the growing <br />season that is available to meet the consumptive water requirements. The <br />effective rainfall was determined using the method outlined in SCS Technical <br />Release No. 21. Irriaation Water Reauirements. It does not include <br />precipitation that is lost to deep percolation or surface runoff. Since most <br />of the irrigated crops are located in arid to semi-arid valley areas, which <br />produce little runoff, the consumptive use of the displaced natural vegetation <br />was assumed to be equal to the effective rainfall. Therefore, the consumptive <br />use actually met by irrigation was considered to be the crop consumptive use <br />minus the effective rainfall. <br /> <br />Growina Season <br /> <br />Most of the growing season limits listed in SCS Technical Release No. 21, <br />Irriaation Water Reauirements, were'used. The exceptions were alfalfa, grass, <br />and grain. <br /> <br />The growing season for small grain was started at SO'F, rather than the <br />recommended 4S'F, and ended at an average temperature equivalent to a <br />recommended 32'F frost. This produced average consumptive use estimates that <br />compares with the estimates in the Uooer Colorado Reaion Comorehensive <br />Framework Studv. 1971. <br /> <br />Initially, the growing seasons for alfalfa and grass pasture were assumed to <br />begin at average monthly temperatures of SO'F and 4S'F, respectively, and <br />ended at the recommended ending temperatures. However, these starting <br />temperatures were adjusted so that the average consumptive use estimates were <br />in general agreement with those in the Enaineerina Advisorv Commission's <br />