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GLBLWARM.ART
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1991-09-04
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Global warming may threaten the seasonal water balance in the western
United States, raise the cost of water to consumers and require additional
construction of large dams and aqueducts.
That warning was issued in May by ASCE member John A. Dracup, a UCLA
civil engineering professor. He testified in Santa Monica before a U.S.
Senate committee on the likely impact of climatic changes on water resources
for agicultural, industrial, and residential use.
In the current international debate on global warming, a number of
scientists have warned that temperatures around the world may rise from three
to eight degrees Fahrenheit by the middle of the next century. The threat
exists because the emission of carbon dioxide and other man-made gases can
produce a "greenhouse effect" that causes the earth's atmosphere to retain
heat. The problem is aggravated by the ongoing decimation of tropical rain
forests.
Whether or not the world actually faces a permanent climatic change,
water resource planners must prepare for the eventuality, says Dracup, and he
lists a number of likely scenarios.
...more on next page...
With higher temperatures, snow lines and freezing elevations on mountains
will climb higher, so that much of the precipitation in winter months will
fall as rain rather than snow. Consequently, runoff patterns will change,
triggering heavy winter floods and a corresponding decrease in streamflow
during late spring and summer.
"With some 85 percent of all California water going for agriculture,
such a water reduction during the normal irrigation period would have severe
consequences," said the UCLA professor.
Theoretically, surplus water from winter floods could be stored in
reservoirs or diverted by canals, but the existing ones, designed with
traditional hydrologic runoff patterns in mind, could not carry the extra
load.
One feasible alternative is to pump and store surplus winter runoff in
groundwater basins, which even now provide 45 percent of municipal,industrial,
and agricultural needs in southern California, say Dracup. At the same time,
he urges stricter adherence to water conservation measures and more research
in such alternative technologies as desalination of sea and ocean water.
...more on next page...
Not only agricultural would feel the effects of global warming.
Production of hydroelectric energy depends on the generation of mountain
runoff and a cutback in generation of electricity during the summer would hit
at the peak demand time for air conditioning. Also affected by a reduced
water flow during the summer would be water-based recreation, augmentation of
streams and floating barges in navigable waterways.
There will also be an economic side to the problem, notes Dracup.
Possible climate changes will add a major risk factor to the anticipated cost-
benefit ratio in planning new dams, aqueducts and other water resource
projects, making it that much more expensive to float revenue bonds.
With scarcer water supplies, residents may find their utility bills
rising steeply, especially in Calfornia, which draws more than half its total
water supply from other states. Dracup, a Santa Monica resident, cites the
example of his own city, which imports water from as far away as the Rocky
Mountains and the Sierra Nevada range.
...more on next page...
The beliefs of residents and newcomers to Southern California that water,
like telephone service and electricty, will be instantly available whenever
and wherever they move, may have to be drastically modified. "I have often
asked people who have recently moved to this semi-arid region a question I
consider legitimate," Dracup told the congressmen. " 'Before you moved here
did you call any local agency to determine whether or not adequate water
supplies would be available once you arrived?' Most either smile at this
question or stare back in disbelief." Given a lead time of 10 to 20 years in
building new water resource projects, planners must face the possibility of
a worst-case global warming scenario now, says Dracup, or rish a situation
akin to the 1973 oil crisis.
ASCE News. July 1989 Vol. 14, No. 7. American Society of Civil
Engineers. 345 E. 47th St. New York, NY 10017-2398.