Changing Climate Report of the Carbon Dioxide Assessment Committee (1983) / Chapter Skim
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EFFECTS OF A CARBON DIOXIDE-INDUCED CLIMATIC CHANGE ON WATER SUPPLIES IN THE WESTERN UNITED STATES
EFFECTS OF A CARBON DIOXIDE-INDUCED CLIMATIC CHANGE ON WATER SUPPLIES IN THE WESTERN UNITED STATES
Pages 419-432
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From page 419... ...
This was based on representative data from 22 drainage basins in the conterminous United States. Their relation in Table 7.l gives the estimated annual runoff for different values of mean annual precipitations and weighted mean annual temperatures.
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From page 420... ...
At an annual temperature of 8°C, runoff is zero when precipitation is 200 mm or less and is l85 mm -- or 26.4% of precipitation -- when the average annual precipitation is 700 mm. For any particular region, the relations shown in Table 7.l are rather crude approximations because many physical factors, including geology, topography, size of drainage basin, and vegetation, may alter the effect of climate on runoff.
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From page 421... ...
have used Langbein's empirical relation to estimate the effects of a climatic change on water in the l8 water regions of the conterminous United States defined by the U.S. Water Resources Council (l978)
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From page 422... ...
In Table 7.4 we have summarized the estimates by Stockton and Boggess of the effects of a 2°C increase in temperature and a l0% reduction in precipitation in the seven water regions of the western United States in which climate change would have the most serious
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From page 423... ...
1-2 S in H Or- u CO -H an o 4i u - -H 41 -U iu -- » 00 O rH in O CM o 4J rH C 41 O C iU 10 -- -H J iw -H -H g 2 I « f rH CM in rH CM rH rH CM rH >H a iU 3 rH iU 4J rH 10 O o -H o a Q O 10 10 cwin o -a u io -*
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From page 424... ...
For the postulated climatic change, supplies would greatly diminish in all regions, ranging from almost a 76% reduction in the Rio Grande region to nearly 40% in the Upper Colorado, with the result that estimated requirements would exceed supplies in the Missouri, Rio Grande, and Upper and Lower Colorado regions. Mean annual requirements would still be less than future mean annual supplies in the ArkansasWhite-Red, Texas Gulf, and California regions.
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From page 425... ...
. The effects of future droughts in the Arkansas-White-Red, Texas Gulf, and California regions from the assumed climatic change could be significantly mitigated by construction of additional reservoirs for water storage, but increases in storage would help little in the Missouri, Rio Grande, or Upper and Lower Colorado regions because their storage reservoirs are already so large compared to the annual runoff.
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From page 426... ...
(As defined, the Upper Basin also includes northwestern New Mexico.) To check the probable effect of a climatic change on the flow of-the Colorado River, we calculated a multiple regression of the relation between annual averages of precipitation and temperature and the "virgin flow" of the Colorado at Lee Ferry, Arizona, which is the southernmost point on the river in the Upper Colorado Basin.
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From page 427... ...
427 FIGURE 7.l Basins or drainages of the western United States.
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From page 428... ...
. The regression coefficients, b^, and their standard errors relating the virgin flow at Lee Ferry to the mean annual precipitation and the mean annual temperature in the watershed from l93l to l976 are as follows: bQ in millions of cubic meters = 9274 ± 3838, b^ in millions of cubic meters/mm = 52 + 7, b2 in millions of cubic meters/°C = -2400 _+ 507.
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From page 429... ...
429 TABLE 7.5 Annual Averages of Precipitation, Temperature, and Virgin Flow of the Colorado River at Lee Ferry, Upper Colorado Region, l93l-l976 Year Precipitation (mm yr"l) Temperature (eC)
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From page 430... ...
Annual Sum (m/sec) l90l 229 6.56 l6753 l902 l95 6.7l ll586 l903 285 5.35 l8264 l904 240 6.55 l9297 l905 3l4 6.l0 l9769 l906 370 5.86 23585 l907 350 6.78 28865 l908 274 6.49 l5857 l909 364 6.05 28709 l9l0 233 6.57 l7574 l9ll 327 7.49 l9770 l9l2 3l3 5.05 253ll l9l3 269 5.7l l7852 l9l4 355 6.68 26l76 l9l5 308 6.47 l7303 l9l6 304 7.08 23684 l9l7 346 5.04 29650 l9l8 263 7.32 l895l l9l9 253 6.43 l5372 l920 33l 5.58 27076 l92l 355 6.57 28389 l922 300 6.60 22580 l923 336 6.04 22535 l924 252 5.63 l75l7 l925 338 6.4l l6077 l926 303 6.28 l9554 l927 404 6.88 22963 l928 253 6.58 2l3l4 l929 392 5.46 26432 l930 309 6.44 l836l Mean 306 6.29 2l098 The multiple regression for the earlier period showed a smaller effect of temperature and a somewhat larger effect of precipitation than during l93l-l976.
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From page 431... ...
Although a 2°C warming is probably a conservative estimate of the effect over the next hundred years of increase of greenhouse gases for the northern United States, the magnitude and even the sign of possible changes in precipitation are uncertain. According to our regression equation, a l0% increase in average annual precipitation combined with a 2°C rise in average temperature would result in an l8% decrease in runoff.
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From page 432... ...
. Annual Runoff in the United States.
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