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I. INTRODUCTION Weather modification has the potential for improving atmospheric conditions for beneficial human purposes--water supplies may be augmented through precipitation enhancement and economic losses, property damage, and deaths may be reduced through mitigation of adverse effects of hail, lightning, fog, and severe storms. Not all Weather modification ac~ivities can be designed to benefit everyone, however, and the technical ability to affect the weather must be accompanied by the abill ty to reconcile social and environmental costs and benefits. The net benefits of weather mofification appear high, but it must be understood that it will take a decade rather than a year to make significant progress. The scientific advances achieved thus far, and the future benefits that may be realized, clearly justify going forward with weather modification research and development in the United States. Various analyses indicate that, though convincing proof of the efficacy or weather modification technology has been elusive, weather modification shows promise for increasing water supplies, reducing hail and wind damage, reducing transportation delays, and reducing the loss of life associated with weather hazards. The Weather Modification Advisory Board, for example, in its June 1978 report cited the following capabilities as evidence of the potential for realizing some of these benefits in the near future: o Supercooled fog and stratus can be seeded to improve visibility. o Holes can be opened in winter stratus clouds to increase the amount of solar radiation that reaches the ground. o Snowpack, and thus the spring runoff, can be increased by seeding wintertime clouds rising over some mountain barriers. o Rainfall is increased in Israel by seeding winter cumulus clouds; seeding convective rain bands in winter cyclonic storms over California (the nearest U.S. analog to the successful Israel experimental) also suggests positive results. o Rain can be. induced from some types or summer cumulus clouds, and their precipitation apparently can be increased by intensive seeding to increase the size of the clouds ('. dynamic seeding"). o Hail suppression is attempted in many countries, 'nth claims of up to 80 percent success in the Soviet Union. U.S. ~~periments have provided no convincing evidence, but evaluations or several projects suggest that hail damage from some kinds or storms can be reduced. - 1 -