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<br />74. Utah Department of Natural Resources. Division of Water Resources (DWR), 2000: Utah Cloud <br />Seeding Program - Increased Runoff/Cost Analyses. by N.E. Stauffcr, and K. Williams. Fcbruary <br />2000. <br /> <br />APPENDIX A <br /> <br />An Independent Evaluation of Seven Operational Cloud Seeding <br />Programs in the Sierra Nevada Mountains of California: <br />Preliminary Results of a Work in Progress <br /> <br />Bcrnard A. Silvennan, PhD <br />Meteorological Consultant <br />7038 E. Peakvicw Placc <br />Centennial, CO 80 III <br />Tel: 303-770-9271 <br />email: silvermanb@aol.com <br /> <br />ABSTRACT <br /> <br />An independent statistical evaluation of 7 operational (non-randomized) cloud seeding <br />programs in the major \....atersheds of the Sierra Nevada Mountains ofC'alifornia has been carried <br />out. These programs include the Lakc Almanor, Uppcr American, Mokelumne River, Kings <br />River, Kaweah River, Kern River, and Eastcrn Sierra operational cloud seeding programs. All of <br />these programs have, for the most part, bcen conductcd continuously since their inception, the <br />earliest ones starting in the Lake Almanor and Mokelumnc River \....atcrsheds in water year 1954. <br />It was found that the historical rcgrcssion method. the most commonly used cvaluation method <br />for thcse operational programs, was not statistically valid and led to misleading results that arc <br />inconsistent with the seeding conceptual model upon which the seeding programs were based. <br />Application of the ratio statistics method of cvaluation rcsulted in estimatcd seeding elfects <br />whose size and statistical strength support a conclusion that cloud sceding operations to enhance <br />strcamflow have been highly successful. However, it was found that the seeding etTectiveness <br />has been stcadily decreasing since about 1990. give or take a year or two, In view of the <br />significance of thcse tindings. it is essential that further statistical studies be conducted using <br />program-specitic controls and additional targets in order to confirm or revise, as necessary, the <br />statistical results of this preliminary study. <br />A preliminary physical analysis revealed that the meteorological conditions. upon which <br />thc seeding procedures are based. have been changing so as to produce a general wanning of the <br />storm environment. It is speculated that this \\.'amling has rendercd the ground-released silver <br />iodide less and less efTective over time. thercby contributing to the observed decreasc in seeding <br />etTcctiveness, Morc in-depth physical studies of this and other potential contributing factors are <br /> <br />32 <br />