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490 '" l..... 'REQUENT APPLICATION \";~---~1'l ,,'. : L '..") / . .,,-- .~ , 'V \ \ . , . ~ . . ..;10 :"-. Vol. 58, No.6, June 1977 . ON [::::::::::::::::::IOCCASIONAL APPLICATION .:.:.:.:.:.:.:.:.:.:. OR SPECIAL SITUATIONS ,.r> " '\ " ~ \ ,<;. - .." ':. " l .,0 . . .~ " . . .. . / ~ f , o . ;. "." ..,: I , : , : , ". ~ FIG. 1. Areas of most likely application of summer-convective precipitation management. uses, such as navigation, recreation, dilution of wastes, and sweetening of saline estuaries, will take place only in particular situations where such use is exceptionally valuable. 6) Applications related to rain-fed crops will occur frequently where the drought hazard is most acutely perceived and, perhaps, in other areas where agri- cultural productivity would benefit even during nondrought periods, especially where agriculture is intensive. They will be infrequent where crops de- pend primarily on irrigation derived from distant sources or where insufficiency of moisture is an infrequent cause for concern. "Crops" will come to include forest and rangeland areas brought under technological management. 7) Applications will be regulated and managed in re- sponse to local or regional needs and to environ- mental, economic, social, and technological con- straints. 8) The amounts of precipitation increase attained by intensive precipitation management will be similar to the capabilities projected on the basis of current experimental results. These projections are dis- cussed in the following sections. Figure 1 shows where applications of summer-convec- tive precipitation management seem most likely to occur under the conditions assumed. The most extensive use is likely to be for rain-fed agriculture. Use for augmen- tation of water storage for end uses including irrigation, hydroelectric power, and municipal and industrial sup- ply will occupy restricted areas where watersheds are already developed for these purposes. The figure sug- gests that occasional applications may be expected over very large parts of the nation, whereas frequent applica- tion will probably be confined to much smaller areas. Figure 2 shows where applications of winter- orographic precipitation management seem likely. Be- sides the obvious limitation that they will be confined to highland regions of the United States, there is notably greater consistency in the likely frequency of applica- tion. Most end uses of the water, whether for irrigation, hydroelectric power, municipal and industrial supply, or groundwater recharge, characteristically take place at a distance from the site of the snowpack augmentation. a. Imjmet on weather elements Current estimates of additional precipitation obtainable by cloud seeding are diverse and controversial. An im- portant aim of Skywater research projects is to improve the basis for those estimates. The estimates incorporated into environmental impact assessments are an attempt to represent what is likely to result from successful de- velopment of the technology. If success is not achieved, there will be no widespread application to cause impacts. 1) SUMMER-CONVECTIVE CLOUDS The opportunity for increasing preCipitation from sum- mer-convective clouds appears now to lie chiefly with clouds of moderate size and moderate dynamic insta- bility. Small clouds, even if doubled in rain output, would contribute but little. The larger convective clouds and cloud systems produce precipitation with such regu- larity that cloud seeding is likely to have but little effect. Therefore, precipitation management is likely to make medium-sized showers more frequent without much af- fecting the frequency of spatters or downpours. Stimulation of medium-sized showers may increase the frequency with which they merge and combine to form multishower systems. Such systems tend to produce