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<br />e <br /> <br />e <br /> <br />not have significant adverse effects on various environmental-ecological <br />sectors. The primary reason cited for this conclusion is the fact that the <br />incremental increases are well within historic annual variations in precipi- <br />tation in the study areas. As additional information and experience has <br />become available, estimates of long-term effects of precipitation augmenta- <br />tion have been moderated. The complexity of this analysis question was <br />recognized in 1977 by Howell: <br /> <br />"It has come to be recognized that, in the settings so far inves- <br />tigated, the potential disturbing effect of weather modification <br />is overwhelmed by other disturbances to the status quo, some <br />manmade and some natural. <br /> <br />IIFrom this state of affairs, two broad conclusions are now being <br />drawn. First, since investigation of the points of specific <br />environmental impact thought to have the highest potential for <br />effect from weather modification has indicated no clearly adverse <br />effects, emphasis on hurry-up studies to ward off imagined catas- <br />trophes, such as species extinctions, no longer appears justified. <br />Second, assessment of long-term effects of weather modification on <br />the environment as a whole is assuming relatively greater impor- <br />tance, and means for such assessment are under review." [13, <br />pp. 499-500J <br /> <br />Thus, it is apparent now that long-term monitoring of operational cloud <br />seeding effects is needed to develop a reliable picture of environmental <br />effects. Responses of the vegetative regime are of particular interest <br />because of its comparative sensitivity and its key place in the food chain. <br /> <br />Certain results of cloud seeding, such as increased snowpack, can be signif- <br />icant and beneficial rather than adverse due to the controlling factors of <br />the project design and project suspension criteria. Project suspension <br />criteria precludes cloud seeding activity during weather conditions that <br />could jeopardize public safety or cause environmental damage. A recent <br />example of development of a suspension criteria system for a winter cloud <br />seeding project is the experience in the Sierra Cooperative Pilot Project. <br />[8, 11J <br /> <br />1. The Initial Phase <br /> <br />As described in Section II of this report, eaCh of the three cloud seeding <br />options has two phases. In eaCh case, the initial phase involves installa- <br />tion of meteorological and hydrological observation and data collection <br />networks. Seeding opportunity, climatological studies, seeding mode <br />studies, ground-based seeding studies, ana teChnology :ransfer studies in <br />different subbasins would be included in the initial phase for :he !O- and <br />3-year options. Environmental and social imoact studies required for the <br />second pnase of the program and for tne operational phase ~oula be undertaken. <br /> <br />Al 1 meteorolcgical and engineering ~c:ivi~ies c8nduc:ea during :he initial <br />phase of each of the options are identical to leaa-in ~c:ivities founa in <br />research-mode cloud seeding. These activities are covered by ~he ?roject <br />SkYNater Programmatic FES [2J and were disc~ssea in :he Sierra Cooperative <br /> <br />1 .'"\ <br />.\.i <br />