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<br />This discussion thus far has not addressed the potential increases in streamflow in the <br />Colorado River that may result from new secding activities in southeast Utah or Arizona (IO\ver <br />Colorado River Drainage). Rccall that the analysis perfonncd by the River Forecast Ccnter <br />excluded these areas. The earlier 12 Basin study mentioned in Table 3 (Elliott et al. 1973) <br />cOnlained an estimate of increases in streamflO\\' from the Gila River drainage of Arizona <br />associated with cloud seeding over the Mogollon Rim and White Mountains areas of Arizona. A <br />conservative increase in average annual streamflow resulting from approximately a 10% <br />increase in precipitation was 154.000 acre feet. No infomlation is available rcgarding the <br />possible impacts of cloud seeding in southeast Utah on strcamllow. The combined estimated <br />anra1?:e streamflow increases from seeding in the four states of Arizona, Colorado, Utah <br />and \V)'oming from both existing and new progrdms assuming a 10% incrcase in <br />precipitation is 1,381,OO~ acre fect for the historical base period, Larger ,..olumes of runoff <br />would occur in abuve normal water ,years and smaller volumes in drier than normal "'"ater <br />lears. It should be emphasi:led that this is an estimate of the total impact of seeding both <br />existing llnd new llreas without prior cloud seeding. Ob,.iously there arc some cloud <br />seeding programs currently operating in some of the existing areas, so some of the potential <br />additiOlUlI streamflo"'. is currently being reali:led. It is difficult to quantify ",.hat percentage <br />of the potential from the existing areas is being reali:led. In fact this contribution may ,'ar)' <br />from year to ).ear since some "existing" programs may be inaeth'e one year but not the <br />next. Also, a gi,,"en program may only operate for two or three months, not the entire <br />winter season. <br /> <br />The ahon should be considered a I)reliminary analysis; more detailed an:.llyscs arc <br />both warranted and recommended. It is encouraging, howen~r, that the 1.381.00~ acre foot <br />yalue is in the range of the earlier, more eomprehensin, studies mentioned in Table 3 <br />which showed estimated increases ranging from 1,150,000 to 1.870,000 acre feet. These <br />earlier studies haH the added benefit that there were no cloud seeding programs being <br />conducted in any of the I)otential target areas, so they ",,"aided the complication that we <br />now haH of h1'ing to reman the impacts of seeding in some areas during the historical <br />base period used in this stud~'. Certainly. if the recommendation that design studies bc <br />completed for each new program arca is accepted. then a morc focuseu streamtlow evaluation <br />could be conducted as part of this design work. <br /> <br />No attempt has been made in this analysis to differentiate between the impacts of <br />modifications to existing prognlnls versus the ways in which these areas arc currently <br />being seeded. E,,"alu;ltions of some of the longer term programs in Utah suggest that 10% <br />incre.1ses arc being achieved. Additio",11 funding would therefore potentially raise the <br />magnitude of the increases in the existing programs in Colorado and Utah be~:ond the 10% <br />increases assumed in the abo\'C analysis. Could another 5% be achiend from modifications <br />to existing programs? Perhaps this is possible. If so, the information in Table 5 could be <br />uSl'd to pro,'ide estillHltes of what .1 15% increase in precil)itation might mean in terms of <br />increases in streamflow abon those resulting from 100/0 increases in precipit;ltion. <br />