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<br />6 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />can be produced by dropping dry ice pellets or releasing AgI ( silver <br /> <br />iodide) crystals into the cloud or by burning a solution of AgI and <br /> <br /> <br />acetone in generators on the ground. Because of the relatively low <br /> <br /> <br />cost, most operational projects in the Sierra Nevada have used the <br /> <br />ground release method. <br /> <br />In general, operational programs generally seed all promising cloud <br />formations. Few cases are reserved as controls, so their evaluation <br />is difficult. Nevertheless, statistical evaluations of operational <br /> <br /> <br />cloud seeding programs in the Sierra Nevada based on comparisons of <br /> <br /> <br />streamflow from target and control basins on both seeded and non-seeded <br /> <br /> <br />years have indicated increases in annual runoff of roughly 5 to 10 <br /> <br /> <br />percent. <br /> <br />During the 1960's Pacific Gas and Electric Company conducted randomized <br /> <br /> <br />seeding experiments near Lake Almanor in the Feather River Basin and <br /> <br />the Fresno State College Foundation (under Bureau of Reclamation <br /> <br /> <br />sponsorship) conducted experiments in the Stanislaus and Mokelumne <br /> <br /> <br />Basins. Both groups concluded that seeding effects depended strongly <br /> <br /> <br />on wind direction, temperature, atmospheric stability, and other storm <br /> <br /> <br />characteristics, but their results were not in complete agreement. <br /> <br />However, much about when and where to seed in Sierra storms came out <br /> <br /> <br />of these projects. <br /> <br />2.2 SCPP Design <br />The objective of the scientists designing SCPP was to identify more <br />precisely the conditions under which cloud seeding causes precipitation <br />