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2.2 Nature of Calculations <br /> That the calculations are based on"snapshots"of <br /> For the current application, we integrated SNO- the snowpack on April 1 requires a caveat. They are <br /> DAS 1 km SWE data over seeding target areas at the representative of cloud seeding augmentation of <br /> traditional end of the mountain snow accumulation snowfall to the extent that the snowpack has continu- <br /> season, April 1 (also the traditional beginning of the ally increased and melted little over the preceding <br /> snowmelt runoff season). To estimate water volumes winter. Such would not be the case in relatively warm <br /> produced by seeding in potential areas,these integra- southerly and/or low elevation mountains, as in Ari- <br /> tions are divided by ten, since there is statistical, zona. Because some melt occurs even in colder cli- <br /> physical and modeling evidence for about 10 percent mates and/or higher elevations,the April 1 SNODAS <br /> augmentation of natural precipitation (snowfall) by SWE will be lower than SWE from accumulated sea- <br /> orographic cloud seeding (American Meteorological sonal snowfall. The latter is actually the more appro- <br /> Society 1998). Physical cause-and-effect relation- priate variable for augmentation potential,but is only <br /> ships have yet to be fully demonstrated, however. measured at a few points. Therefore the seeding- <br /> Since seeding has been conducted in existing areas,it generated 10% increases of the April 1 SNODAS <br /> is assumed that SNODAS SWE already reflects the SWE, as presented below, might be expected to un- <br /> 10% increase, or 110% of natural snowpack. There- derestimate in proportion to seasonal snowpack abla- <br /> fore the integrated SWE is divided by 11 in these tion(melt, sublimation[ice to vapor] or evaporation). <br /> areas. These calculations were made for both 2004 Snowfall measurements from gauges have significant <br /> and 2005 April 1 SWE data. The year 2004 was an errors as well.Moreover,some of the gauged precipi- <br /> unusually dry one in the Upper Basin and 2005 was a tation could have fallen as rain, <br /> relatively wet one. See Fig. 2 for a graphical repre- <br /> sentation of the precipitation in the basin. <br /> Mountain Snowpack Mountain Snowpack <br /> as of April 1, 2004 as of April 1, 2005 <br /> Legend Legend <br /> Percent afAverage percent <br /> -—to � If =>159 <br /> -1-30 -Fr. JJ� ( -13C-150 <br /> -1.0 -2y r -11C-129 <br /> �,o- nr ego-IN <br /> -,0-39 + r ( 70-89 <br /> 5n-;!1 r f4 ®50-69 <br /> -EGG I -c50 <br /> }t <br /> Figure 2. Snowpack expressed as percent of 30-year average in various sub-basins of the Colorado River basin, <br /> as of 1 April 2004(left)and 1 April 2005(right).Data are from SNOTEL sites operated by the National Re- <br /> source Conservation Service(NRCS)and figures are from the NRCS National Water and Climate Center. <br />