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2 CLOUD SEEDING In a farm area having mixed crops, many farmers might benefit from enhanced precipitation, while others might not. In a mountainous re- gion where hydroelectric power generation would be greatly benefitted, traffic over mountain passes might be impaired, while ski resorts might be aided. In order to provide rational assessments of all of the impli- cations, a number of scientific studies of these varied impacts have been conducted. 1.2 WHY SEED CLOUDS? Benefits of additional precipitation to be derived from cloud seeding are determinable in terms of increased hydroelectric power and agricul- tural production, salinity reduction, and strengthened ski industries, and for the users of our water supplies associated with fish and wildlife, recreation, municipalities, and industry. Thus, the primary motivation for cloud seeding is economic, but other potential benefits to the public and private enterprise are also important. The economics are significant. Major studies of crop benefits have been conducted in several areas. In South Dakota, the state university made an extensive study that indicated summer cloud seeding could yield crop benefits well beyond the costs. A Montana State University study showed that an additional 10o/~ of precipitation over the growing season would be expected to increase farm revenue by $10 million to $43 million (1973 dollars). A North Dakota Agricultural Experiment Station study esti- mated that added rainfall of 20 mm during June-July and 30 mm for June-August would increase the State economy by over 0.5 billion (1977- 1981 average dollars). Recent Illinois State Water Survey results have indicated rainfall increases of 10% to 40% would increase corn and soy- bean yields by 4% to 20% if natural rainfall is near normal. The direct beneficiaries in winter mountain snowpack projects include those using the resultant additional streamflow for hydroelectric power generation and irrigation water. They may be located great distances from the target area. In the present era of high energy demand, it has been estimated that a less than 1% increase in stored water would pay for such projects. 1.3 APPROACHES AND RESTRICTIONS TO SEEDING CLOUDS With benefits come risks. Economic, environmental, and social factors will determine whether a cloud seeding program is accepted. Risk-bene- fit assessments in each of these categories, relative to any alternatives for providing more water, are appropriate. However, the risk perceived by stateholder groups and the public will be very important regarding whether the cloud seeding project is accepted by the community. Legal