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o (..., C") 00 00 00 SUMMARY Total water depletions by processing sectors of the Great Basin economy totaled 3,064,000 acre-feet in 1965 and is projected to be 3,265,000 in 1980, 3,690,000 in 2000, and 4,372,000 in 2020. The agricultural sector used 96 percent of total water used by processing sectors in 1965, and is projected to use 93 percent in 1980, 88 percent in 2000 and 79 percent in 2020. Municipal and rural domestic depletions are estimated to increase nearly three-fold throughout the 55-year pro- jection period. Depletions for fish and wildlife are projected to increase 1.7 times the 1965 level. Water resources are adequate to meet the OBE-ERS projections of agricultural production and the municipal and industrial requirements. Some recreation needs of the population projected to be located in the Great Basin Region will not be met by water-based recreation. The agricultural and municipal and industrial water depletions will have an adverse affect on the Region's, terminal lakes. Upstream diversions have resulted in a lowering of the levels of the Great Salt Lake in Utah and Pyramid and Walker Lakes in Nevada. The lakes will be lowered at a faster rate as water depletions in- crease throughout the projection target dates. This trend results in more expensive mining of minerals on the Great Salt Lake and reduced fisheries and other water-based recreation on Pyramid and Walker Lakes. Impact of Alternative Assumptions Irrigated cropland required to produce the level of agricultural production represented in the OBE-ERS projections for 1980 would be reduced 335,000 acres and annual irrigation water requirements would be reduced 630,000 acre-feet if all crop yields exceeded the OBE-ERS projections by 25 percent. However, if crop yields attained by 1980 fall short of the OBE-ERS projections by 25 percent, 573,000 acres of irrigated land and 1,074,000 acre~feet of water would be required in addition to the quantities shown in the baseline projection. By 2020, if crop yields exceed those in the OBE-ERS analysis by 25 percent in all crop categories, irrigated cropland required to produce the OBE-ERS level of agricultural production would be decreased 365,000 acres and irrigation water decreased 711,000 acre-feet. If, however, in 2020 yields averaged only 75 percent of the OBE-ERS projec- tions 599,000 additional acres and 1,227,000 acre-feet of water would be required to produce the .OBE-ERS projected quantities of food and fiber. In the OBE-ERS analysis a large acreage of irrigated native hay. land and permanent pasture was projected throughout the period under analYSis. These lands had water rights and therefore were projected to continue to receive water. The acreage of native hay and hay other than alfalfa totaled about 376,000 acres. Permanent, uncultivated pasture of very low productivity totaled 402,000 acres. iii