DOE/Pacific Northwest National Laboratory / EurekAlert!
November 21, 2002
Accelerated Climate Prediction Initiative

"Water may be the resource that defines the limits of sustainable development," states a 2001 United Nations Population Fund report, which noted that water use has grown six-fold over the past 70 years.

Nowhere is that more true than in the western United States, where existing water resources already are stretched to their limits. There is little or no leeway for changes in current water allocations. But there is every reason to expect that climate change, such as that associated with greenhouse warming, could dramatically alter the availability of water in the West. In the most rigorous study to date of potential greenhouse impacts, leading scientists detail how major water problems could evolve over the next 50 years throughout the West as a result of climate change already underway.

Many people have heard about the impacts of global warming, but the general public typically doesn't grasp the ramifications of such changes. A degree or so change in global mean temperature seems harmless enough. What most people do not know is that the regional or local climate changes associated with global warming will be far more significant than apparently small average changes might imply.

New simulations by a group of leading global warming and climate change researchers suggest the effects of rising temperatures will exacerbate problems we are beginning to see. In the West, the effects of global warming already have begun to emerge in earlier melting of mountain snow packs and spring flooding dates. Scientific studies show that these, and other expected climate changes, could have a devastating impact on water resources in some parts of the West over the next half century.

For instance:

- In the Columbia River System of Washington State, residents and industries likely will be faced with the choice of water for summer and fall hydroelectric power or spring and summer releases for salmon runs, but not both. Accelerated Climate Prediction Initiative research, or ACPI, shows that with climate change, the river cannot be managed to accommodate both. In fact, the window for successful salmon reproduction in the Pacific Northwest may become so compressed by climate change that some species could cease to exist regardless of any current or future water policies.

- The Colorado River Reservoir System will not be able to meet all of the demands placed on it -- including water supply for Southern California and the inland Southwest -- because reservoir levels will be reduced by more than one-third and releases by as much as 17 percent. The greatest effects will be on lower Colorado River Basin states. All users of Colorado River hydroelectric power will be affected by lower reservoir levels and flows, which will result in reductions in hydropower generation by as much as 40 percent.

- In the Central Valley of California, it will be impossible to meet current water system performance levels so that impacts will be felt in reduced reliability of water supply deliveries, hydropower production and instream flows. With less fresh water available, the Sacramento Delta could experience a dramatic increase in salinity and subsequent ecosystem disruption.

"Population and economic growth already are placing severe pressure on water resources in the West. Climate change is one more very important factor that has to be taken into account when thinking about the future," said Bill Pennell, director of the Atmospheric Science and Global Change Division at Pacific Northwest National Laboratory.

"It also is important to point out," said Dennis Lettenmaier, Professor of Civil Engineering at the University of Washington, "that these predictions are based on one of the most conservative climate models. Other models show a much larger warming effect. However, even this conservative model indicates substantial changes. For example, by mid-century the yearly average snow pack in the Washington and Oregon Cascades may be reduced on the order of 50 percent and because most of our water storage is in this snow pack, such a reduction will result in big changes in flows and water temperatures in Cascade rivers and streams."


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