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<br /> PUEBLO l> <br /> 7 <br /> -4f0[];, o- W <br /> 1V"',(j/lVs >~ <br /> q: <br /> 0: <br />NEW MEXICO (2 <br /> Cr,) <br /> it: <br />[=:=J ABOVE 9000 FEET ~ <br /> / <br />_ ABOVE 12000 FEET <br />Fig. 4. Downwind preclpltatlon augmentation In Sangre de Cristo Range <br />from cloud-seeding In San Juan Mountains <br /> 19 <br /> \ <br /> <br /> <br />i <br />i <br />I <br /> <br />~ <br /> <br />DEN VER <br /> <br />80 <br /> <br />SCALE IN MILES <br />-'- <br />40 <br /> <br />o <br /> <br />COLORADO <br /> <br />1\ <br /> <br />I ~ <br /> <br />f <br /> <br />SNOWPACK, CLOUD-SEEDING, AND THE COLORADO RIVER <br /> <br />the season, then seeding would have been carried out during the <br />winter. However, heavy late-season storms are common in the <br />region, and could bring the total snowpack to undesirably high <br />levels. <br />The decision to curtail or resume seeding depends on the <br />level of risk that the snowpack represents. For example, in the <br />San Juan Mountains the probability of flooding froin snow melt <br />runoff could be held to less than one year in 20 by curtailing <br />cloud-seeding to only 90 % of the potential increase in snowfall. <br />This compares to the normal flood probability without cloud- <br />seeding of one year in 25. <br />The probability of avalanches is greatly increased by heavy <br />accumulations of new snow. In the region a few days of heavy <br />snowfall give more than half of the seasonal snowfall, in both <br />high and low snowfall years. Although seeding these storms <br />would increase the avalanche risk, these are the storms on which <br />seeding would be most effective. If seeding were curtailed on the <br />basis of carefully monitored snowfall rates and accumulations <br />in potential avalanche areas, the augmented snowfall could be <br />reduced by as much as one-half. Fortunately, there are other <br />ways of limiting avalanche risks. <br />Overseeding a storm likely to produce a natural snowfall <br />should diminish the snowfall in a target area. However, there <br />are many problems that must be overcome before this method is <br />a practical way to prevent too large a snowpack. <br /> <br /> <br />~ <br /> <br />f, <br />~ <br />~. <br />I: <br /> <br />'I, <br /> <br />.-Ii <br />1 <br /> <br />II.!.:... <br />;'1 <br /> <br />Iii: <br /> <br />The Basin's Share of the Atmospheric Moisture Supply <br /> <br />An initial reaction to cloud-seeding is that increasing the pre- <br />cipitation in one location necessarily reduces it in others. This <br />both oversimplifies and distorts the effect of WOSA in the Upper <br />Colorado River Basin, although it may apply to other types of <br />cloud-seeding or to other locations. <br />The principal moisture source for winter storms in the <br />Upper Colorado River Basin is the Pacific Ocean, including the <br />Gulf of California. Part of the moisture is deposited as snow as <br /> <br />18 <br /> <br />, <br /> <br />t <br />I,' <br />,~j~ <br />