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Crops in the Southwestern United States," issued May 1982 by the United States Department of Agriculture. Effective precipitation was derived from criteria developed for the area by Wayne D. Griddle, former Utah State Engineer. These theoretical consumptive use calculations were based on the assump- tion of full water supply during the crop growing season. However, it is estimated that in an average year about 37 percent of the irrigated lands in the Upper Basin receive less than a full supply of water, either due to lack of distribution facilities or junior water rights. The degree to which these lands suffer shortages varies widely from year to year, depending in large part on the magni- tude of runoff. For. this study, an estimate of the short supply 'service lands was made for each sub-basin, primarily on the basis of reports and investigations collected for the comprehensive framework study, A stream-flow gaging station was selected within each sub-basin and the magnitude of the recessional portion of the annual hydrograph was used as an index to select the date at which consumptive use calculations should be terminated for the short supply lands. Comprehensive framework studies of the incidental consumptive use of water associated with irrigation indicated that this use varied between 5 and 28 percent of the irrigation consumptive use depending upon the location of the study area within the Colorado Basin. These percentages were used in the Upper Basin and an average value of 15 percent was used in the Lower Basin to adjust the calculated consumptive use. The agricultural data is generally adequate for use in this report. With the exception of Utah, each state prepared annual county irrigated acreage estimates of the harvested crops during the reporting period. These statistics are assumed to be reliable. The irrigated pasture values were based largely on the 1978 National Census of Agriculture since the State statistics do not include pastureland. Due to the length of time between reporting dates, this item needs to be considerably strengthened. In this regard, Wyoming and New Mexico have initiated aerial photographic mapping of their State's irrigated. acreage to verify the annual statistical sampling. Other areas of agricultural data collection which need to be updated and verified are (1) the consumptive water use of lands which receive less than a full seasonal supply of irrigation water and the areal extent of these lands, and (2) the amount of incidental seepage and phreatophytic losses associated with irrigation. Reservoir Evaporation: A comprehen- sive listing was developed of all reservoirs in the Colorado River Basin which included the latitude, elevation, and surface area at total capacity for each reservoir. Monthly content records were ob- tained for those- reservoirs for which records are available. The average annual water-surface area was deter- mined for each year of the reporting period. For those reservoirs lacking records, a "fullness factor" was estimated on the basis of reservoir use and historical hydrologic conditions. These "fullness factors" were then used to obtain estimates of average annual water-surface area for the unreported reservoirs. For the. majority of the basin, historical evaporation rates were used to determine reservoir evaporation. In the Upper Basin, regression equations relating gross annual evap- oration to elevation, latitude, and climatic subarea were developed for each of the reporting years. In the Lower Basin, evaporation values were calculated for each climatic subarea. Account was taken of precipitation and runoff salvage to determine net evapor- ation rates. The net evaporation rates were applied to the estimates of average annual water-surface area to yield the values of annual reservoir evaporation. An exception to this procedure was the determination of evaporation from the main stem reservoirs shown in 13