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<br />.. The originalligure from the SRI document has been halved because il was based on an assumed 20% increase. <br />whereas loday the often accepted increase is I Oo,~ <br /> <br />It should be notcu that the water yield provided in Table 3 for the Twelve Basin Study docs not <br />include the estimated incrcases from seeding the Gila River drainage in Arizona. The <br />conservative estimatcd increases for this drainage were 154.000 acre feet. The Gila River is a <br />tributary to the lower Colorado River. <br /> <br />A Recent Amllysis by Steven Hunter. Bureau of Reclamation <br /> <br />A recent Reclamation report (1lllnta et al. 2005) provided estimates of increases in April <br />I Sl sno\v \....atcr content due to cloud seeding in some of the areas considered in the earlier studies <br />as documented in Table 3. Existing projcet targct areas wcre used as is. which were delincd with <br />base thresholds at elevation contours of7.000 feet MSL in Utah. and 8.000 to 9,000 feet MSL in <br />Colorado and Wyoming. Figure 3 (see section 10) shows these locations as well as potential new <br />target areas. Tables I and 2 (sce section 10) provide geographical namcs associated with these <br />areas. <br /> <br />Hunter et al. 2005 then used a new spatially distributed snow cncrgy and mass balance <br />model known as the Snow Data Assimilation System (SNODAS) with a I km (- 0.6 mile) <br />resolution to integrate the AprillSl sno\\: water content in the existing and potential cloud seeding <br />target areas (Tablcs I and 2 provided in section 10) for the water years of2004 and 2005. A <br />longer period data base was not available using this SNODAS system. <br />Quoting from Hunter et al. 2005: "To estimatc water volumcs produceu by seeding in <br />potential areas. these integrations arc divided by ten. since there is statistical. physical and <br />modeling evidence for augmentation of natural precipitation (sno\\--fall) by orographic cloud <br />sceding of 10 percent:' Physical cause-and-etTect relationships have yet to be fully <br />demonstrated. however. Since seeding has bcen conducted in existing areas. it is assumed that <br />SNODAS SWE alrcady reflects the 10% increase. or 110% of natural snowpack. Therefore the <br />integrated SWE is divided by II in these areas. These calculations were made for both 2004 and <br />2005. While two years is hardly an extensive climatological record. it is fortuitous that the two <br />years exhibited a large variation about the mean in precipitation amounts. That is. 2004 was an <br />unusually dry year in the Upper Basin and 2005 was a re1ntively wet one:' <br /> <br />llunter et al. 2005 providc a rough approximation of potential increases in streamflow by <br />using the additional amounts of snow water contents to estimate potential runoff. The authors <br />mention the following caveat: "The reader is cautioned that \\-ater volumes resulting from <br />incrcasing the existing April I snowpaeks do nOI l1ecessari~\' equal rlIl1o.ff increases. The latter <br />increases may be changed by a given basin's hydrologic processes such as soil infiltration. <br />ant~cedent soil moisture. slope and asp~ct. and vegetative cover. Other factors affecting a <br />basin's prceipitation.runolT relationship ar~ spatial distribution of the snowpack. amount and <br />timing of any rainfall on the pack. temperature. and evapotranspiration of snowmelt \vater," <br />Table 4 (from lIunter. ct al. 2005) lists the water volumcs produced by 10% increases of the <br />snowpack SWE on April I for both existing and potential target areas for the water years of2004 <br />and 2005. <br />