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<br />spomoring companil's monilOr streaml10w and rt'servoir storage. Although weather modification inneascs arc <br />small compared to natural prl'Cipitation variability, thcre might be some concern about snow removal from roads <br />and snow loading on roofs. <br /> <br />(). Hmos c1uud sl't'{linJ: dl'l'rt'aw pn'Cil)italinu downwind'! <br />A. No. The idca thilt pn.'Cipitiltion increascs in one area causc decrcases c1scwhere is a misconccption. The <br />amount of atmosphcric moisture passing over a mountain barrier that i.. con\.'ertt.-d to prt.'Cipitalion i.. usually 10'k <br />or less. If this nalUral prt.'Cipitation is increascd by 10'1 by cloud sceding, only Ifk of the original atntosphcric <br />moisture supply is depletedl.. Morl'Over. winter cloud scC'ding is done on clouds on thC' upwind side of mountain <br />rangel,. These clouds usually dil,Sipate on the downwind or lee side of the range. bt.'Causc of a nalural effect called <br />the "rain shadow." Thi.. i.. the rC'a..on that lee side area.. like the Colorado front Range and Nevuda are much drier <br />than on the upwind side of the mountains. So the atmospheric moisture supply on the k.: side of the mountain <br />range will not likely prl'Cipitatt' anyway. finally, prl'Cipitation data from a numhcr of long-term cloud sl'l-ding <br />projCl'ts have b..'t.'n examint.'lI in dctail for evidence of "ell.tra-ar.:a" efft."Cts. These cll.aminations do not ..how that <br />sel-ding clouds with silver iot.lidc cau..es a dl'CreasC' in downwind prl"l'ipilation: in facl, somC'times there may tlc an <br />.f 100 .Id . d f h l.l1~1~1t>:11:1~1\I <br />merease as ar as ml cs O\~nwm 0 t e targel area . '. <br /> <br />Q. What uhoul inll'rh,rt'nn' "ith IHllurc? <br />A. These que...lion... often ignore the fact that human ilctivities have cau~-d itllld"f'rtnlt weather modifil.ation for <br />milny ccnturies. A rn'ent National Research Council n:port20 statcs thai "there is ample evidence that inadwrtent <br />weather and global climate modification (e.g.. grl'enhouse gases affecting globaltcmperaturcs and anthropogt'nic <br />ilero\ob affl"Cting cloud properties) is a reality:' Even the simple act of cultivating a farm field altC'rs local <br />climate. Imt'milmlll wl'ilther modificalion. particularly of the form praetiCl-d in winter sl'l'tling, alll'rs the <br />environment far Ie" than the ilccumulated effects of int/lJ"ertnll wcathcr modification. Indl'cd. cloud seeding in <br />California may havc bl't'n pilrtially compen\ating for prl'Cipitillion IO'ises from the inadvertl'nt we.lther <br />modification brought on by air pollution21. <br /> <br />I{EI.l;I{E....C1'...-; <br /> <br />I Supt.'r. Arlin R, and James A.lleimbach. Ill83: Evaluation of the Rridger Range wintcrcloud sel'tling <br />experiment using control gages, J. "1'I,lit'tJ Mf'/f'oroloJ.:Y. 22. 19~9-2011. <br /> <br />1 Ryan, B. F.. and W. D. King. 1997; A critical review of the Australian ell.peril'nce in cloud ...C'cding. Bull. Amcr. <br />Meteor. SrM.:,. 78, 239.354. <br /> <br />l fl.1ielkC', 1'. W.. G. W. Brit.'r. L. O. Grant. G, J. Mulvey and P. N, Rosenzweig. 1981: A statistical rcanaly..is of <br />the replkatl-d Climilll. I & II wintertime orogmphie cloud sel'ding t'll.pcriments. J. "I'/,/il'tJ. Ml'rl'omlof.:Y. 211, h.B- <br />659. <br /> <br />~ Bureau of Reclamation. 1977: Projt.'Ct Skywall'r. A program of Research in Prt.'Cipitation Management. Final <br />Environmental Stateml'nt tiNT FE,~ 77-39). <br /> <br />~ Ilarri.... Edward R.. 1981: Sil'rra Cooperative Pilot Project - EnvironmC'ntal A\Sessment and Finding of No <br />Significant Impact, U.S. DC'panmenl of the Interior. Bureau of Rl'Clamation. Denver. CO. 208 pp. <br /> <br />t> lIowdl. Wallat'e E.. 1977: Environmental Impacts of Precipitation Managl'ment: Results and Inferent'e... from <br />Projl"l't SJ..ywatl'r. HI/II, "merimll MI'ff'orologinll Society. 58. 488-501. <br /> <br />7 Donald A. Kk'in. 1978: Etll'ironml'II11l1Impact.\' of Anijicillllce Nllcleating "ge"'-5, Dowdl'n.llutchinson & <br />Ross. Inc.. Stroudsburg, 256 pp. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br />