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<br />brganization (WMO, -1986) haspubf1she(fa-setO'f-.-~---- dispensers are small and targeting difficult in complex
<br />guidelines for decision makers on the utility of cloud terrain should be considered. Marler (1992, this
<br />seeding. It takes a cautious l'Osition toward cloud seeding conference) describes some recent studies in targeting
<br />for precipitation enhancement as unequivocal proof of the effectiveness over Lake Almanor that begin to address this
<br />efficacy of this technology is lacking. The AMS Policy question.
<br />Statement, previously mentioned, takes a less conservative
<br />position than the ~O, perhaps because the authors
<br />include both scientists as well as members of the
<br />operational weather modification community.
<br />
<br />The American Society of Civil Engineers (ASCE,
<br />1983), of which many water resources managers are
<br />members, has published guidelines for the use of cloud
<br />seeding to augment precipitation. They conclude that cloud
<br />seeding may produce a 5 to 20 % increase in precipitation if
<br />the proper planning is performed. The guidelines call for
<br />not only an economic assessment, but also an
<br />environmental and societal assessment of the benefits and
<br />liabilities of cloud seeding. The assessment would be
<br />followed by a design study that would 1) account for the
<br />meteorological and topographical features of the target
<br />area, 2) define suspension criteria for terminating seeding
<br />during threatening weather, 3) define evaluation criteria for
<br />assessing seeding effects and 4) require monitoring for
<br />environmental impacts. Although excellent guidelines, they
<br />are rarely implemented when projects begin.
<br />
<br />Finally there is the Weather Modification
<br />Association Statement of Capability (WMA, 1991).
<br />Approved by many of the same individuals as the ASCE
<br />document, it provides the same optimistic conclusions and
<br />recommendations.
<br />
<br />,
<br />
<br />Shortly after Vonnegut's development of AgI as an
<br />effective nucleation aerosol and a generator to dispense it
<br />in-cloud, utility companies in California began seeding to
<br />augment the winter snowpack in an effort to increase
<br />hydro-electric power generation during spring runoff. Four
<br />winter seeding programs that were initiated in the 1950's in
<br />California for snowpack augmentation (the upper San
<br />Joaquin, 1951, by Southern California Edison, the Kings
<br />River project, 1955, sponsored by the Kings River
<br />Conservation District, and the Mokelumne/Stanislaus and
<br />Lake Almanor Programs, 1953 and 1954 respectively, both
<br />sponsored by Pacific Gas and Electric (pG&E)) are still in
<br />existence today.
<br />
<br />Statistical analysis of the Kings River and Almanor
<br />programs (Henderson, 1966; Mooney and Lunn, 1969)
<br />suggests that seeding has produced about 5 to 10%
<br />additional precipitation per season for the watersheds being
<br />treated. It is obvious that the spc,nsors of these programs
<br />are convinced that the technology being used to seed clouds
<br />is satisfactory, in that it has not changed materially in
<br />decades. Changes in AgI solutions for better combustion
<br />and nucleation efficiency, and more reliable and better
<br />located seeding generators have been the only substantive
<br />modifications. Unfortunately, results of recently completed
<br />research programs such as the Sierra Cooperative Pilot
<br />Project (SCPP) (Reynolds and Dennis, 1986) have not
<br />materially influenced the conduct of these ongoing
<br />programs. Results showing that the SLW occurs at
<br />relatively warm temperatures reducing AgI's effectiveness,
<br />and that dispersion rates of AgI aerosols from ground
<br />
<br />In contrast to these four programs, five other
<br />California cloud seeding programs have been designed and
<br />implemented on the basis of several years of randomized
<br />seeding trials. Table 1 lists these programs, their sponsors,
<br />the randomized projects conducted prior to their going
<br />operational, and the primary purpose of each program.
<br />Obviously the agencies involved have made a commitment
<br />to use cloud seeding as a water resource management tool.
<br />Two other programs that have been in existence since the
<br />mid 1970's are the Kern and Kaweah River seeding
<br />projects. This makes a total of eleven programs in
<br />California that have been ongoing for more than 10 years.
<br />A program in the Santa Clara Valley was terminated in
<br />1987 after 36 years of operation when the benefits of the
<br />program (the agency felt they were obtaining 10 to 12 %
<br />increases in seasonal precipitation) could not justify the
<br />(;osts. During the last few years of the program, costs had
<br />risen due to the need for equipment upgrades and because
<br />of a law suit brought against the water agency. The suit
<br />was eventually settled in the agency's favor. More
<br />importantly, during the 36 years, urban growth had
<br />overtaken the once rural target area, making control of
<br />runoff much more difficult.
<br />
<br />With the onset of California's current 5-year
<br />drought, ten other programs have begun since 1987. These
<br />include the coastal communities of San Diego, San Luis
<br />Obispo, Monterey, and Catalina Island and programs over
<br />the San Gabriel Mountains in Los Angeles County, the
<br />Calaveras and Tuolumne Rivers of the central Sierra, Lake
<br />Berryessa and Davis Creek watersheds near the Bay area,
<br />and the Mono-Owens River Basin project on the eastern
<br />side of the Sierra Nevada. In all, twenty-one programs are
<br />expected to operate during the 1991-92 winter season
<br />(fig. 2). Estimatl'A1 total cost of these programs, including
<br />operational as well administrative expenses but excluding
<br />environmental document preparation and environmental
<br />monitoring, exceeds $2 million. The cost per project
<br />varies from $25,000 to $400,000 per year. This variation
<br />in costs reflects to some extent the watershed size but,
<br />more importantly, it indicates that the technology can be
<br />modifitxl to'. accoimnodate what the market price will
<br />support! Unfortunately, this variability in pricing damages
<br />the public image of cloud seeding and its reputation in the
<br />scientific community.
<br />
<br />) "u'
<br />
<br />If each project were to produce only an additional
<br />65 X106 m3 (5,000 acre-ft) of additional runoff (for some
<br />projects this is much less than 1 % of the seasonal runoff
<br />for the watershed) and water is worth $100 per 1300 m3 (1
<br />acre-ft), the combined revenues from all projects would be
<br />$10.5 million dollars, producing roughly a 5 to 1
<br />benefit/cost ratio. It is this expectation of a good return on
<br />a modest investment that motivates water resource
<br />managers to pursue cloud seeding.
<br />
<br />01
<br />
<br />Even though the additional water developed by
<br />seeding falls far short of what is needed for complete
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