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Last modified
7/28/2009 2:38:46 PM
Creation date
4/16/2008 11:10:48 AM
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Weather Modification
Title
Validation of Precipitation Management by Seeding Winter Orographic Clouds in the Colorado River Basin
Date
9/1/1993
Weather Modification - Doc Type
Report
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I' <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />hypothesized chain of physical processes. Even when statistical testing suggested differences <br />between seeded and nonseeded populations, the exploratory nature of most analyses left doubts <br />about probability estimates and questions about the physical mechanisms involved. Without an <br />adequate understanding of the latter, transferability of results to other locations was <br />questionable. <br /> <br />The need to document the key physical processes involved with cloud seeding has become <br />increasingly apparent. Vincent Schaefer, the discoverer of modern weather modification, <br />recently made a plea for a return to physical evaluation of seeding effects (Schaefer, 1990). <br />Braham (1981) made a strong case for improving our physical understanding of how cloud <br />processes react to seeding before embarking on any more large ''black box" experiments. He <br />stated that 'We need to design experiments that can follow seeding effects as perturbations <br />moving through the varying cloud systems." Fortunately, such observations have become <br />increasing practical with new instrumentation developments. A limited number OIf physical <br />experiments of this type have been conducted as discussed later. <br /> <br />Some exploratory statistical experiments have suggested that a 5 to 15 pct increase in seasonal <br />snowfall can be achieved. Perhaps the best known experiment is the Climax, Colorado, program <br />of the 1960s, the only winter experiment to date that incorporated a confirmatory phase after <br />the exploratory phase. Some of the initial suggestions did appear to be con::firm~d (Milelke et al., <br />1971), and the results generally were accepted by the scientific community for a time. Mielke et <br />al. (1981) dealt with a possible type I statistical error (a chance selection of sEleded and <br />nonseeded days that favored an erroneous statistical conclusion of increased snowfall caused by <br />seeding). However, serious challenges to the Climax experiments appeared in the open <br />scientific literature (Hobbs and Rangno, 1979; Rhea, 1983; Rangno and Hobbs, 1987). The <br />Climax statistical results now are viewed with skepticism by many scientists, in part lbecause of <br />the lack of supporting physical observations. The Climax experiments were conducted in <br />complex terrain with a modest budget before the development of much of the instrwnentation <br />in common use today. Hence, routine monitoring of the key physical mechanisms involved was <br />not then practical. <br /> <br />Several winter seeding experiments were attempted in the West during the late 1960s and <br />early 1970s, but major funding cutbacks terminated all but Reclamation's CRBPP (Colorado <br />River Basin Pilot Project) after about 1973; the CRBPP continued through 1975. Most of the <br />experiments were inconclusive. Two exceptions are the Bridger Range Experiment, which will <br />be discussed later, and the Cascade Project. The Cascade Project was a pioneering effort in <br />physical evaluation of seeding experiments which produced some of the most convincing <br />evidence available that seeding can modify snowfall when properly applied under some <br />conditions (Hobbs, 1975a; Hobbs and Radke, 1975; Hobbs, 1975b). The Cascade Project did not <br />address the magnitudes of the changes that might be achieved on a seasonal basis over a large <br />area. To do so would have required a multiple winter statistical experiment for which funding <br />was not available. <br /> <br />The CRBPP, discussed by Elliott et al. (1978), found no significant difference in precipitation <br />from seeded and nonseeded days. However, at least two serious design problems were <br />discovered involving inadequate T&d of the seeding agent and inability to forecast cloud top <br />temperatures and winds. Thus, CRBPP results must be considered inconclusive, meaning the <br />evidence supported neither the conclusion that seeding could enhance snowfall nor the <br />conclusion that seeding was incapable of increasing snowfalL Elliott et al. (1978) reanalyzed the <br /> <br />7 <br />
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