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<br />V~L-~J-l~~J ~~.~( <br /> <br />rr"ul'I U.=JCrH r"CU1UI'l 0 UCH <br /> <br />IU :J OClo~,-+r'-f <br /> <br />I.UU....'<.-><.->...... <br /> <br />00.)218 <br /> <br />, <br /> <br />- <br /> <br />. <br /> <br />"mE COLORADO RrvER BASIN AND CLIMATIC CHANGE' <br /> <br />BACKGROUND TO nIE STUDY I <br />. I <br />Changes In global temperature and precipJtatlon patterl\3 are likely to occur as ~ <br />result of the accumulation 0 greenhOuse gases released to the atmosphere by humary <br />actIvIties. These climatic changes have been called "the greenhouse effect," The <br />greenhouse effect is llkely to have significant imfllClS on water resources, but the nature or <br />consequences of such alterations at the regiona Jevel is Stll! far from clear, One method <br />for determining how regional resources might be affected by climatic change is to develop' <br />scenarios of chanies in temperature and precipitation and to uso computer simulation <br />models to study the fmpa~s of these scenariol on runoff and wator supply, In this new: <br />study, the Pacific InstItute dId a detailed analysis of the sen.sitiviey of water reSources in the! <br />Colorado River Basin to a range of plausible climatIc changes. The C<llorado RIver is the! <br />most important dyer system In rhe semi-arid southwestem Unlted States, It Js the prindpat! <br />. water source in a basin that C.oVers approximately 243,000 square miles. including parts of! <br />seven V.S, states, and nonhern Mexico. . I <br />I <br />There were two part.! to this sludy: The first part eVAluated the effects of changes 'I <br />in temperature and preclpitation on runoff us1ns a computer model developed and operated <br />by the National Weather Service, The second part evaluated the impacts of these changes' <br />in runoff on water supply, salinity, and hydroelectricity production throughout the basin I <br />using the Colorado River Simulation System (CRSS), B reseliiolr-simulatlon model I <br />developed and operated by the V,S. Bureau oC Reclamation, I <br /> <br />Increases in average temperature of 2' to 4'C were studied togcther with increases j <br />and decrea~es in precipitation of 10 and 20 percent. Changes in temperature and I <br />precipitation generated by three large-scale general circulation models (GCMs) were also <br />eva! u ated. The range of scenarios studied reflects current best understanding of the i <br />expected magnitude of climatic chanies In the Colorado R.jver Basin. I <br /> <br />I <br />I <br />rmpoct8 or Temperature and P~lpllRllon ChanatS ! <br />· Increases in temperature of 2'C, with no ehange In preeJpitation, cause averllge I <br />annual runoff in the Colorado River Basin to decllne by 4 to 12 percent. i <br />, <br />I <br />A temperature increase of 40C causes average atUlual runoff to decrease by 9 \021 i <br />percent, depending on location In the basin. I <br /> <br />Precipitation increases of lS to 20 percent would be req\lired mcrely to offset the I <br />Impact of a 4"C temperature rIse, on an annual basis, Projections of future <br />precipitatIon plltte:ns in the region are highly uncertain, <br /> <br />MAJOR FINDINGS <br /> <br />. <br /> <br />. <br /> <br />The regions most sensitive to changes in temperature and precipitation are the <br />higher elevation basins, such as the East River, White Rivor, and Animus RIver <br />watersheu$, though all high.elevatlon basins will experience similar changes, <br />