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<br />4.5.1. Cloud seedability parameter estimated from model simulations <br /> <br />Values in table 4.3 use an enhancement factor of 0.1125 that estimates the percentage increase from <br />cloud seeding. This value is based on the product ofthe two factors, 0.45 and 0.25. The first factor <br />represents the concept that on average, 45 percent of the precipitation (above 9000 feet as used here) in <br />the Headwaters Region is seedable. The 0.25 factor represents that the expected average increase in <br />treated clouds is about 25 percent. The 25 percent increase value is obtained from consideration of the <br />results of the Bridger Range Experiment (Super, 1974; Super and Heimbach, Jr., 1983) and the Climax I <br />and II Experiments (Mielke et aI., 1971; 1981). <br /> <br />The 0.45 factor was calculated as the average of 7 ratios of precipitation obtained from simulations by <br />Colorado State University with the RAMS model, on 7 storms of the 1998-99 winter in the Park Range. <br />The precipitation ratios were defined as total precipitation (using hourly reading from the model) with <br />model liquid water present to total storm precipitation. The storm seedability ratios do not consider <br />information when seeding leads to precipitation when naturally none would occur. The ratio was <br />considered of storm time with liquid water present to total storm time but values appeared unrealistically <br />large and the more conservative ratio was selected. The model did indicate for some periods, lower or no <br />liquid water amounts when model precipitation rate was relatively high. Storms simulated were selected <br />for varying storm types according to time of winter; small, moderate and high actual precipitation <br />amounts, and predominant westerly and nonwesterly wind cases. Three storms were simulated at 3 <br />kilometer grid point resolution and the remainder at 12 kilometer grid spacing. Model simulations <br />appeared to overestimate precipitation (suitable comparisons could not be made because point estimates <br />at field gauge locations were not made by the model). Simulations need to be compared with actual field <br />observations. Generally, the 3 kilometer simulations yield substantial detail for comparisons. The <br />simulations appear to yield useful information for purposes of the proposed program and it is <br />recommended that additional modeling be pursued should the program move forward. <br /> <br />Table 4.1 gives operational project cost information. The average annual cost of operation per seeding <br />device is estimated at $21,301. If water is valued at $30 per ac-ft, the benefit/cost is 2.18 for the 40- <br />percent areal coverage case and 3.28 for 60-percent coverage. It is likely that a generator installation <br />design can be developed that can achieve 40 percent or better areal coverage. <br /> <br />29 <br />