A new federal government study on the possible effects of global warming in the Southwest warns of dramatic reductions in hydroelectric power generation, severe water shortages for Arizona cities, widespread crop damage in Southern California and northern Mexico and the degradation of fish and wildlife habitat from Colorado to the Mexican border.
Released yesterday, the study, sponsored by the U.S. Environmental Protection Agency and conducted by the Pacific Institute in Oakland, Calif., focuses on the effects of temperature increases of 2 to 4 degrees Celsius in the Colorado River Basin, an area covering parts of seven states and northern Mexico.
Global warming, itself a controversial theory, occurs as synthetic "greenhouse gases" such as carbon dioxide intensify in the atmosphere, primarily from the burning of fossil fuels, and trap more of the sun's heat. The EPA study of the Colorado River Basin assumes a doubling of such gases over the next 50 years.
The study's anticipated temperature rise is well within the range of increases predicted by most global warming studies. However, many scientists are skeptical about the accuracy of those forecasts. Scientists also disagree about the effects of global warming, some believing it could produce beneficial effects such as balmier nights and milder winters that make for longer growing seasons.
The authors of the study acknowledge some of the uncertainties surrounding global warming research and caution that an extended drought is just one possible result of a rise in temperature. They point out, for example, that a large increase in rainfall also is a possible consequence and could offset shortages in runoff caused by a reduced snow pack.
The greatest threat posed by global warming, the study warns, is the prospect of extreme fluctuations in weather patterns, "increasing the frequency of both sustained drought events and high-flow events [floods]" and underscoring the need for much more flexible management of the basin's water supply.
"One of the greatest fears is that climate change will make floods and droughts both more common. We don't know for sure that is what is going to happen. But there are indications from the modeling that it will," said Peter Gleick, a co-author of the study and the director of the global environment program at the nonprofit Pacific Institute for Studies in Development, Environment and Security.
Whatever happens as a result of rising temperatures, the new study states, the current system of apportioning water in the basin -- with its fixed allocations and priorities -- will not respond well in a crisis, especially if normal runoff is depleted.
Mr. Gleick recommends management changes that make it easier to divert surplus water from one part of the basin to another in case an ecosystem is imperiled by drought or to head off a municipal water shortage. "Under the present management system," the study says, "even modest decreases in runoff would lead to drastic declines in the levels of major reservoirs, big drops in the generation of hydroelectricity and cutbacks in water deliveries to some users."