Weather Mod Critical Issues Report

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. I I I I I I I II I I I I I I I I I I I information has been found very useful in the design of ground-based mountain area seeding projects, 5) Latest state-of-the-art remote sensing systems are a basic requirement for conducting successful snowpack augmentation programs. They can locate and measure in real time the distributions of cloud water and ice as well as wind flow patterns related to seeding aerosol transport. The wind profiler, the dual-channel microwave radiometer and the polarimetric radar have found substantial use in specific snowpack augmentation programs in Nevada, California, Utah and Arizona prior to 1995, 3.2.4 Additional evidence of wintertime cloud seeding effectiveness There is a broad body of evidence in the literature and in company reports describing the results from various operational projects involving winter orographic clouds. Some projects in California have been in existence from the 1950's and 1960's. The Kings River project in southern California has been operational for 48 years and has produced an average 5.5% additional runoff per year (Henderson, 1986, 2003). An operational project run for the past 25 years or so in Utah has published results for 13 and 19 years of operations that indicate 11-15% increases in seasonal precipitation (Griffith et aI., 1991; Griffith et ai, 1997). Add to these results the San Joaquin River project showing at a minimum 8% increase in target area seasonal precipitation using trace chemistry studies of snow pack (McGurty, 1999), the Climax project indications of 10% increases, and the Tasmanian results of 10% increases in seasonal precipitation when storm cloud top temperatures are in the range of _100C to -120C and the evidence becomes very convincing that cloud seeding conducted under proper conditions increases precipitation in winter orographic situations, These findings and statements are in accord with the American Meteorological Society policy statement on weather modification regarding capabilities of winter orographic cloud seeding (AMS, 1998). Most of the evaluations have utilized target-control regression techniques or snowcourse water content and precipitation storage data. Most of the evaluations of long-duration projects have provided evidence of increases in streamflow amounting to 5 to 10 percent of the natural flow (NRC 1966, 1973). More recent evaluations using precipitation or snow water content information have shown increases in the 10-15% range (Griffith et aI., 1991). Conversion of these increases in precipitation into streamflow indicates increases in streamflow on the order of 10% (Stauffer, 200 I), The consistency of results is encouraging. Statisticians have questioned the validity of p-values obtained from sets of non- randomized data. Of particular concern is the fact that the seeded and non-seeded cases are drawn from different historical periods, instead of being interspersed in a random fashion. Gabriel and Petrondas (1983) have investigated this point with actual rainfall data, and confirmed that p-values from evaluations of non-randomized projects need to be adjusted for such effects, but not to the extent that the analyses are rendered invalid. Considering the hundreds of project-seasons of data that are now available, it appears that the latest NRC report should have confirmed, and even extended, the encouraging 19