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<br />a} Does seeding work and how much more water can it produce? <br /> <br />There is evidence that seeding of orographic (mountain) clouds to augment sno\l,:fall is more <br />effective than all other types of weather modification (except for cold fog suppression, which <br />certainly works). This claim is supported by a policy statement of the American Meteorological <br />Society (AMS)3o, a weather modification status statement of the World Meteorolog.ical <br />Organization31, the NRC report12, and the Wi\.tA1J. The AMS further states that there is <br />statistical evidence that such seeding can produce seasonal precipitation increases of about 10%. <br /> <br />The California DWR22 estimates that an additional 300,000 to 400,000 acre-feet of \....ater could <br />potentially be produced annually by more and improved cloud seeding in California. This <br />increased amount of\vater would come at a cost of about $19 per acre-fool. Many of the best <br />prospects for additional \....eather modification water increases are in the Sacramento River basin, <br />in watersheds that are not presently seeded. Most of the southern Sierra basins in the San <br />Joaquin River and Tulare Lake regions are already seeded (Figure 2). With the exception of the <br />upper Trinity River \,,'atershed and perhaps the Russian Rivcr, there is little new potential in the <br />North Coast region since not much cxtra runofT could be captured because of limited storage <br />capacityu. There is also potential to increase water production by improving the effectiveness of <br />existing seeding projects, <br /> <br />The main question is how best to achieve additional water through .....eather modilication. The <br />physical mechanisms described in Section CI arc well documenledl~. Although the NRC and <br />WMA have some disagreements, they concur that winter orographic cloud seeding is promising <br />for the afore.~ent!oned increases a~d that t~e:e is a nC,ed tor a. fullr, rand?mized statistical <br />weather modificatIon program to butld on cXlstmg operatIOnal proJccts'.. This program would <br />have strong observational and computer modeling components, and incorporate the latest science <br />and technology. Most importantly, thc program \""ould increase confidence in estimation of <br />attainable seasonal snow water equivalent increases from cloud seeding, <br /> <br />Cloud seeding should not be viewed as a drought "Iix" to be conducted only during dry periods, <br />since seeding opportunities are less frequent in such periods. Seeding (:'\"el)' year, however, can <br />augment surface and ground water storage to increase average supplies, helping alleviate the <br />adverse impacts of drought. Weather modilication should be viewed as "one tool in the toolbox" <br />of water resource management. <br /> <br />2. The State of Weather Modification and its Capabilities <br /> <br />a) Current knowledge and remaining challenges <br /> <br />13 <br />