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<br />.. <br /> <br />. <br /> <br />probable water supplies .continued. upon the current <br />hydrologic status of the Basin. Within the range of probable <br />water supplies, the most probable is that volume of runoff <br />which is expected to be exceeded 50 percent of the time based <br />on actual forecasted runoff volumes whenever available and <br />historic precipitation and temperature data. Schematics of <br />the conditioned most probable, the probable minimum, and the <br />probable maximum water supplies forecasts, illustrating the <br />changing basis of the forecasts during the year, are <br />presented in Figure 1. <br /> <br />An example of the conditional probabilities of water <br />supply for April through July, 1987, based upon October 1, <br />1986 conditions, are given in Figure 2. The Figure shows a <br />conditioned most probable water supply forecast (with an <br />exceedance probability of 50 percent) of approximately 9.5 <br />million acre-feet (117 percent of the 25-year average). The <br />conditioned maximum and minimum probable water supply <br />forecasts are those with an exceedance probability of 10 <br />percent and 90 percent, respectively. The marginal <br />probabilities of water supply for April through July 1987, <br />shown in Figure 2, are derived without regard to the October <br />1, 1986 hydrologic status of the Basin. <br /> <br />3.2.2 Basin States' Beneficial Consum tive Water Use. <br />Excess water, as defined earl er, is water in excess of the <br />beneficial consumptive water use needs of the United States, <br />the minimum Mexican Water Treaty delivery obligation of 1.5 <br />maf per year, and reservoir conservation storage. <br />Consequently, as part of the annual quantification of excess <br />water, beneficial consumptive water use requirements in the <br />United States must be assessed for that year. The estimated <br />Basin state Colorado River water needs during the most <br />likely period of excess water, 1988 through 1992, are <br />presented in Table 5. The estimated water needs of the Basin <br />states, other than California, are equal to or less than each <br />of the state's basic apportionment of river water. <br />California's consumptive water use needs reflect full use of <br />its basic annual apportionment of 4.4 maf, plus its <br />additional needs for surplus water or unused apportionments <br />of Arizona and Nevada. Arizona is assumed to have the <br />ability to use surplus water after 1992. <br /> <br />-24- <br />