Laserfiche WebLink
<br />000112 <br /> <br />CREST is a limited duration test. Seeding will occur in only two of the <br />CRB's six high-yield subbasins. CREST will be governed by a randomization <br />feature in order to obtain statistical significance for the observed <br />change in precipitation. This will ensure further that the precipitation <br />increases will be well within the natural variability of the region. <br />Experience indicates that questions about the following types of environ- <br />mental matters generally arise in connection with the type of cloud <br />seeding activity proposed under CREST. <br /> <br />1. Impacts on weather elements. - The consensus of scientists is that <br />a full-fledged operational winter cloud seeding program in the Rocky <br />Mountains of the CRB could result in a 10 to 15 percent precipitation <br />increase per year. This increase would be nested within a naturally <br />high year-to-year precipitation variation of approximately 60 to <br />170 percent of the long-term mean. "Winter precipitation also varies <br />over an elevational gradient, e.g., the number of hours of winter <br />precipitation in 1969-70 was 938 near the crest of the San Juan <br />Mountains versus only 152 at Durango." [14, p. 4J In addition, seeding <br />to achieve this increase would be subject to suspension criteria cutoff <br />ceilings during the high snowfall years. <br /> <br />Studies of precipitation downwind from winter orographic cloud seeding <br />areas have shown increases at distances up to 250 kilometers. Research <br />does not indicate that seeding-produced increases in one area deprive a <br />downwind area of precipitation. The CREST design will provide for <br />investi9ation of extra-area/downwind precipitation effects due to <br />seeding in the primary project areas. <br /> <br />There is no reason to believe that cloud seeding would significantly or <br />adversely affect atmospheric humidity, existing variations in cloudi- <br />ness and sunshine, the length of the winter season, or the air quality <br />of the Basin. The potential for impacts on these elements has been <br />discussed at length in both the Project Skywater Programmatic Final <br />Environmental Statement [4J and the Sierra Cooperative Pilot Project <br />Environmental Assessment [12J. Both documents concluded that cloud <br />seeding produced no effect on these weather elements, or that the <br />effect was not significant. <br /> <br />2. Impacts on hydrolo ic and physio raphic phenomena. - The 5-year <br />San uan co ogy PrOJect lnc u ed lnvestlgatlons 0 t e effect of <br />increased snowfall on snowpack, avalanches, erosion, and physiographic <br />features of the area. In the report, "The Influence of Snow and <br />Increased Snowfall on Contemporary Geomorphic Processes in Alpine <br />Areas," Caine states: <br /> <br />"Five years of observations in two l-km2 alpine basins <br />are used here to estimate the impact of increased snowfall <br />on erosion above treeline in the San Juan Mountains. Two <br />distinct approaches, differentiating the direct impacts <br />(those involving only the snowpack and erosion) and the <br />indirect ones (involving other components of the ecosystem <br />as intermediaries between the snowpack and erosion), are <br />the basis of the study. <br /> <br />15 <br />