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<br />While conditions appear favorable for seeding to enhance the snowpack of the Sevier River Basin, it must <br />be admitted that strong physical evidence is still lacking that seeding can result in significant snowfall <br />enhancement with economic benefit. The most recent weather modification policy statement of the <br />1O,OOO-member American Meteorological Society (1985) indicates that scientific proof remains elusive <br />for winter mountain stonns in general, The policy statement notes that "Precipitation amounts from <br />. certain cold orographic cloud systems apparently can be increased under favorable conditions with existing <br />technology in the Western United States. Increases of the order of 10 percent in seasonal precipitation <br />are indicated in some project areas." But the policy statement cautions that "In all cases where indications <br />of precipitation increases have been suggested, confirmatory experiments are required before any of the <br />technologies can be considered scientifically proven. The establishment of the physical mechanisms active <br />in any demonstrated modification effect is also needed to achieve general scientific acceptance" (emphasis <br />added). There is clearly a need to provide convincing scientific evidence that winter orographic cloud <br />seeding can increase precipitation before the emerging technology will be widely accepted as a viable <br />option for water resources management. <br /> <br />It is strongly recommended that a weather modification demonstration program be conducted at a typical <br />site in the Sevier River Basin to validate the technology and gain sound infonnation on the methods and <br />costs of conducting an effective operational seeding program. Until such infonnation is obtained there <br />will always be serious questions about the amount of additional water being produced by operational <br />seeding. Moreover, it may be that substantially more water could be provided by a more effective seeding <br />program. Preliminary benefit-cost ratios are estimated in section 8 but these had to be based on several <br />untested assumptions. More definitive estimates must await improved physical evidence of seeding <br />effectiveness. <br /> <br />32 <br />