FLOOD07915

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Alpha - U.S. Government Agencies #17 USEPA - 1993 Climate Study
• Date: 12/7/1993
• Prepared For: State of Colorado
• Prepared By: EPA
• Floodplain - Doc Type: Educational/Technical/Reference Information

DEC-03-1993 13:47

FROM flEPA REG I ON 8 OEA

TO 9-8.74_ _ _ ____

P,004/006

""

"'mE COLORADO RIVER BASIN AND CLIMATIC CHANGE'

. BACKGROUND TO nm STUDY , I

Chango. In slobat temperature and precipitation pattorns are likely to occur as Ii
r~ult of the accumulation ot iteenhouse gases released to the atmosphere by huma~
actlvltles, These climatic chansea have been called "the greenhouse effect." The
Jreenbouse effect is likely to have signJficlZlt impacts on water resources, but the nature or
consequences of such alleratlons at the regional level Is still rar Crom clear. One method
for de~ermln!ns how rejional resources might be aff~cled by cHmatlc chango la to develop'
scenarIos of chanaes In temperature and preelpltanon and 10 use computer simulation
models 10 !tudy tne impa~s of these scenario.! on runoff and, wator supply. 1n tbis new~
study, tbe PacIfic Institute did a detailed analysis of the senslti'Y1ty of water resources In thol
Colorado River Basin to a ranse of plausible climatic changes. Tho Colorado River is thel
most Important dver system.ln the semi-arid southwestern Unfted States. It Is the princlpall
,water source in I basIn that e,overs appro~lmately 243,000 square miles, Including parts or'
s=ven V.S, statts, and northern Mexico. " ,', , '

Thera were two paru 10 this study:' The first pllrt evaluated the effecu of cbanges
In temperature and preclpltatJon on runoff us1ll8 a computer model developed and operated
by the National Wealher Service, The second part evaluated the impacts of these changes
In runoff on, water supply, salinity, and hydroelectricity production throughout the basin
\Ising the O:llorado River Simulation System (CRSS), II reservolr-slmulatlon model I
developed and operated by the V,S, Bureau ot Reclamation. I

Increases in average temperature of 20 to 4"C were studied tosether with increases
and decrea~es in precIpitation of 10 and 20 percent. Changes in (emperature and
preclpltation generated by three large-scale general circulation models (OeMs) were also I
evaluated. The range of scenarios studied reflects current besl understanding of the i
expected magnitude of climatic chanaes In the Colorado f{lver Basin. I

I
I
Impact. or Temperature and Proelpllllt!on Chanits i
. Increases in t~mperature of 2'C, wltb no ellange In precipitation, cau.e averago I
allnual runoff in the Colorado River ~asln to decline by 4 to 12 percent. i
. I
T
A temperature lncreue of 40e causes averase annua11l1noff to decrease by 9 (0 21 i
percent, depending on locatlon il1 the basin. I

PrecipJtatlon Increases of 15 10 20 percent would be required merely to offset the I
lmpact of a 4"C temperature rise, on In annual basIs, Projections of future :
precIpitatlon patterns in the realon a.re highly uncertain. ' I

The regions most lensltive to changcs In temperature and precipitation arc the I
higher elevlltlon basins, suc11 as the East River, White Rlvor, and Animus River !
wluershetl.~, though all high.elevatlon basins ....iII experience similar changes,

MAJOR FINDINGS

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