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POTENTIAL WATER AUGMENTATION FROM CLOUD SEEDING IN THE COLORADO RIVER BASIN EXHIBIT I Steven M.Hunter WWC-VaiUBeaver Creek Technical Service Center Record of Decision Bureau of Reclamation Vail Public Library-Public Hearing Denver,CO 80225 September 21 2010 Abstract. A spatially-distributed snow energy and mass balance model,updated with all available snowpack obser- vations, is used to assess the potential for water augmentation by winter orographic cloud seeding in the Colorado River Basin.The modeling system outputs snow water equivalent(SWE)on a 1 km grid throughout the continental United States. The April 1 SWE from the last two years are horizontally integrated across existing and potential seeding target areas in the basin and multiplied by approximately 0.1 to calculate water yields from an assumed seeding-induced increase of 10 percent.Major uncertainties in this method, including snowpack ablation and target area selection, are described. Given those uncertainties, it is estimated that in an average precipitation year, about one million acre-feet of additional snowpack water could be produced by seeding. Somewhat more could be pro- duced in a wet year and about 500,000 acre-feet in a dry year.These figures are reasonably close to those from older studies of augmentation potential in the basin. 1. BACKGROUND Seeding of orographic (mountain) clouds in the cool season has been done in the Upper and Lower Colorado River Basin since the 1960s, on an operational and research basis. Several studies have been done in that time to estimate the potential water augmentation from seeding in the basin.The following are some of the older such stud- ies and their estimates of water yield, as cited in a Bureau of Reclamation report(Water and Power Resources Ser- vice 1980): Table 1. Previous water yield estimates from cloud seeding in the Colorado River Basin Source Dates Water Yield Estimates Acre-ft Bureau of Reclamation Grant 1969 1967-1968 1,870,000 Stanford Research Institute Weisbecker 1974 1971-1972 1,150,000* North American Weather Consultants,Twelve 1972-1973 1,315,000(liberal) Basin Investigation Elliott et al. 1973 903,000 conservative t *Figure from this document is halved because it assumed a 20%increase,whereas today the often accepted in- crease is 10% f Figures from this study do not include estimates from the Gila River Basin in Arizona,which is in the lower basin and most of which is below 9,000 feet elevation. These figures are for seeding all target areas in 2. AUGMENTATION ESTIMATION the basin, with areas selected based on the differing PROCEDURES criteria of each study. Since these studies are over 30 years old, it was desired to update them with more We assumed a 10%increase in April 1 snow wa- recent information. Also, motivation was added by ter equivalent (SWE) in existing and potential target the letter of 25 August 2005 from the seven Colorado areas,with SWE provided by the Snow Data Assimi- Basin states to Interior Secretary Norton. This letter lation System (SNODAS; Carroll et al. 2001). The requested a long-term plan for operating Lakes Pow- SNODAS consists of a spatially-distributed snow ell and Mead during hydrologic drought, and in- energy and mass balance model, updated with all cluded a recommendation that Reclamation develop a available snow water equivalent, snow depth, and plan for water augmentation through cloud seeding. snow cover (from surface, aircraft, radar, satellite) Also, the funding and context for the current work data.Model outputs include SWE,snow depth,snow- were provided by the Colorado Water Conservation melt, pack temperature, and sublimation. Daily and Board's(CWCB)"Winter Storm Climatology"study, historical model output for the state of Colorado may of which Reclamation had a part. be found online (Hunter 2004). The output has been available nationwide since October 2003, and for