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<br />. <br /> <br />. <br /> <br />~ <br /> <br />lI'ffiE COLORADO RIVER BASIN AND CLIMATIC CHANGE" <br /> <br />I. <br />i <br /> <br />I BACKGROUND TO 'l1IE STUDY <br /> <br />I Changes In global temperature and preclpitatlon patterns are likely to OOOl! U a <br />~Sult of the s<<umulatIon of iteenhOusc gases released to the atmosphere by human <br />a tlvltles. ,These climatic chllngc! ~ave been called ~the gttenhouse effect." The <br />eenhouse effect b likely to have significant impacts on water resources, but the nature or <br />c1>~equence! of such a1t~ration! at the re,gionallevd is still far from ,clear. One method <br />~' r ,determinIng how regional resources nught lxl affected by climatic C,hange is to develop <br />s enarlos of changes In t.empcrature and precipitation and to use computer simulatIon <br />o4~14 to study the impacts oE th~ ~enlirlo5 on runoff and water supply. In this new <br />&tlldy, the Pacit'lc Institute did a detailed analysis ot the sensitivity of water resources in the <br />Colorauo River Basln to a range of plausIble climatic changes. The Colorado River is the <br />nlost important river system in the seml.arld southwestern United States. It Is the prlnclpal <br />,water sourco in a basin that covers approximately 243,000 square miles, includinB parts of <br />s en U,S. stateSI and northern Mexico. <br /> <br />There were, two parts to tbIs study: The first part evaluated the effe~s of changes <br />I temperatUre and precipitation on runofl using i computer model dev~loped and o~rated <br />b the National Weather Service. Tho second pait evaluated the impacts of th08e changes <br />I runoff on water sU2Ply, salirt.lty, and hydroelectrlclty production throughout the basin <br />\l~lng the Colorado River Simulation System (CRSS), a res~l'Yolr.simulation model <br />djVelOped and operated by the U.S. BUteau ot Rec1amlldon, <br /> <br />In~rcases In average temperature of 2~ to 4"C were studied together with increases <br />a I d decreases in pre<:lpltatlon of 10 and 20 percent. Changes in temperature and <br />p~e~lpltatlon generated by three large-scale seMral circulatlon models (OeMs) were also <br />eJaluated. The range of scenarios studied reflects current best understanding of the <br />e1~cted magI'itud6 of cllmatie chanitls In the Colorado RIver Basin. <br /> <br />I MAJOR FINDINGS <br />, <br /> <br />ItpactB Qr TemperatuR alld Pmlpltallon Chanie5 ' <br />. . Increases in temperature of Z~ witll no eht\nge in pre~lpitation, (lease average <br />! Mnual runoff in the Colorado Rlv~r Basin to decllne by 4 to 12 percent. <br /> <br />. <br /> <br />., <br />I <br />, <br />I <br />I <br />i <br />.1 <br />I <br />\ <br /> <br />A temperature Increase ot 4DC caUSes average annual runoff to decrease by lJ to 21 <br />percent, depending on looatlon in the basin. <br /> <br />Fteclpltatlon incre~s oIl! to 20 percent would be required merely to offset the <br />impact of a 4'C temperature risC.!. on an ltnnual basis, Projections of future <br />pre<:ipilatlon patternS In the region arc highly uncertain, <br /> <br />The reg!o~ most sensitive to changes In temperature and precipitation ~re the, c <br />higher elevation basins, ~uch as the East River, White River, arlQ Animm River <br />wntershe(h, though all hlgh.elevllt!OIJ basins will experience similar dllmges. - <br /> <br />^.~ ~~U~~~ 7r~~r- <br />