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<br />3. RESULTS AND INTERPRETATION <br /> <br />The reader is cautioned that water volumes resulting from increasing existing <br />April 1 snowpacks via cloud seeding do not necessarily equal runoff increases. The <br />latter increases may be changed by a given basin's hydrologic processes such as soil <br />infiltration, antecedent soil moisture, slope and aspect, and vegetative cover. Other <br />factors affecting a basin's precipitation-runoff relationship are spatial distribution of the <br />snowpack, amount and timing of any rainfall on the pack, temperature, and <br />evapotranspiration of snowmelt water. <br /> <br />There was a CREST-related analysislO of snowpack-runoff relationships for <br />fourteen watersheds in Colorado, Wyoming and Utah. The selected watersheds were not <br />significantly affected by upstream trans-mountain or trans-basin diversions and not <br />regulated by upstream reservoirs. This analysis performed a long-term linear regression <br />of snow course/snow pillow SWE and stream gauge data and assumed 10% SWE <br />increases from seeding. Correlation coefficients between the two datasets was low for <br />some watersheds, usually because the snow courses/snow pillows were relatively low in <br />elevation and didn't reflect higher altitude snowpack. This shortcoming can be alleviated <br />by the spatially continuous SWE fields of SNODAS, if one were to do a new regression <br />analysis with that system. Given the assumed 10% SWE increase, April to July seasonal <br />runoffs varied from 6% to 21 %. This variation was attributed either to poor <br />representation of the snow course/snow pillow SWE data or to differing basin hydrologic <br />or meteorological characteristics, as related in the preceding paragraph. Porous geology <br />such as sinkholes may divert meltwater away from stream gauges, leading to decreased <br />runoff measurements, whereas impermeable soils such as clay may increase runoff <br />percentages. Again, these complex factors will affect any additional runoff produced by <br />seeding-induced precipitation increases and should be weighed when selecting target <br />areas. It is logical to assume that the further the target area is from the mainstem of the <br />Colorado River, the greater the runoff losses at the river. Examples of such areas are the <br />Wyoming potential targets at the northern extremity of the basin (see Fig. 1). On average, <br />however, 10% runoff increases might be expected to result from 10% snowpack increases <br />(Arlin Super, personal communication). <br /> <br />Table 4 lists the water volumes produced by 10% increases of the snowpack SWE <br />on April 1 for both existing target areas for the potential areas. <br /> <br />6 <br />