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<br />The main purposes of this study are I) to conduct an independcnt statistical cvaluation of <br />the operational cloud seeding program conducted in the major watersheds in the Sierra Nevada <br />~10untains of California over their pcriod of operations lor which adequate streamflow data <br />exists and 2) to conduct preliminary physical analyses that might corroboratc and explain the <br />statistical results. The statistical cvaluations will bc conductcd for each program separately and <br />thcn pooled to establish the common efTect of secding for all of them, It is expt.'Ctcd that these <br />analyses will providc information that wiUlead to improvement of the cost etft.'Ctiveness of the <br />seeding operations in general. <br /> <br />2. Data <br />The sclection of operational sceding programs to cvaluatc was based solely on the <br />availability of seeding targcts having a suitably long record of monthly. unimpaired streamllow <br />data. hcrcaller referred to as full natural flow (FNF) data. during both the historical and <br />opcrational periods. The sources of the FNF data wcre ( I) the Unitcd Statcs Geological Survey <br />(USGS) streamflow gauging sites that arc published on the USGS web sitc <br />(http://waterdat.usgs,gov/calnwis), and (2) the monthly, unimpaircd streamllow data published <br />on the California Data Exchange Center (CDEC) web site (http://cdec.water.ca.gov). Operational <br />sceding programs conducted in thc loIlO\....ing 9 watcrshcds \\iere potential candidates for <br />cvaluation: Lake Almanor, American River Basin, Mokelumne River Basin, Tuolumne River <br />Basin, San Joaquin Rivcr Basin, Kings River Basin, Kcrn River Basin, Kaweah River Basin and <br />the Eastern Sierra. 111e San Joaquin operational secding program was cxcluded from <br />consideration in this study because the author is presently undcr contract to the Southern <br />California Edison Company (SeE) to evaluate thai program and SCE has dccmed that those <br />results arc proprictary to thcm. 111C Tuolumne River operational seeding program was also <br />excluded from the prcsent study because only one gauging station in the Tuolumne Rivcr <br />watershcd with a suitably long record of monthly FNF data during both thc historical and <br />operational periods was found (Tuolumne Rivcr-La Grange Dam. TLG) and it could not be <br />determined whether that station was in a location that would reflect the cffcct of the seeding in <br />that watershcd. For the remaining scven watershcds, it was dctcrmincd that the sceding target <br />selected as having suitable FNF data. while not necessarily the best sccding target, should have <br />been impacted by thc seeding, The Merced River at Pohono Bridge (USGS site no. 11266500), <br />hcreafter rcfcrred to as MDP (CDEC Station ID), was selectcd to represent thc control basin <br />(Merced River Basin) for the evaluation of all the operational seeding programs, The Merced <br />Rivcr Basin may bc onc of thc very few remaining non-sccded basins in thc southern Sierra <br />Ncvada Mountains. <br />Table I lists the operational seeding programs selected for evaluation. the targct stations <br />choscn to reprcsent them and some relevant infornlation about cach of those targets. Similar <br />information about the control is also givcn in Table I. For a fcw of the operational sccding <br />programs. additional target stations with FNF data wcrc evaluated. especially when those stations <br />had a longcr period of record than thc one selected for thc primary evaluation. These are not <br />included in Table I but will bc discussed in their relevant context latcr. Table 2 gives the <br />correlation coet1icients between the control station, MDP. and each of the target stations. It can <br />be seen from Table 2 that thc correlation coellicients are sut1iciently high for MDr to scrve as a <br />control for all the targets. It is likely that stronger correlations could bc found by using different <br />and/or additional control stations provided that these stations have FNF dala and have not been <br />alll.."Ctcd by seeding either advertently or inadvertently. \Vith opcrational cloud seeding being <br /> <br />34 <br />