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Warming May Hurt Salmon, Study Says

by Annette Cary, Herald staff writer
Tri-City Herald, November 11, 2002

Global warming could have devastating effects by midcentury on water already in short supply in the Mid-Columbia, according to a study being released today.

"We're going to get less water when we need it and more water when we don't need it," said Bill Pennell, director of the Atmospheric Science and Global Change Division at Pacific Northwest National Laboratory in Richland.

Salmon could be one casualty, with certain species dying out no matter how the water supply is managed.

More than two dozen scientists from PNNL, the University of Washington, the U.S. Geological Survey, Scripps Institute of Oceanography and other institutions worked over three years on the study of water impacts in the West.

While previous studies have looked at what will happen when carbon dioxide levels double at the end of the century, this study compared the observed climate at the end of the 20th century with what could occur in the next 50 years.

"It also is important to point out that these predictions are based on one of the most conservative climate models," said Dennis Lettenmaier, professor of civil engineering at UW. "Other models show a much larger warming effect. However, even this conservative model indicates substantial changes."

It's also the most rigorous study to date, scientists said.

They found that even though the temperature may rise only a few degrees by midcentury, the changes in the water system will be dramatic in some areas of the West. That could influence power generation, salmon, flood control, irrigation and fire seasons.

PNNL scientists, who focused some of their work on the Columbia Basin water system, estimated that average temperatures could rise about 3 degrees here.

That's enough to change the water flow in the Yakima River Basin, which drains from the Cascade Mountains.

Temperatures currently are cool enough that the average snow pack in January is about 275 millimeters. But a 3-degree average increase means more of that precipitation will come as rain, leaving smaller areas of the mountains covered with snow and melting snow that's already fallen. Different model runs projected the snow pack peaking from 50 millimeters to about 140 millimeters.

A year of heavy snow now will hold that precipitation in the mountains until it's needed in spring and summer for fish and irrigation.

But with more precipitation falling as rain, the snow pack will no longer act as a natural reservoir in 50 years.

The global warming model predicts that the Yakima River by 2050 could easily have 50 percent more water flowing in December and January, when the water is not needed. Runoff would peak earlier, possibly in March, rather than in May.

By knowing more about the potential effects of global warming, leaders can begin including changes in plans they already are making to improve water storage and fish survival to meet current challenges, Pennell said.

But "You're faced with some pretty difficult decisions," he said.

A large river such as the Columbia that drains water from colder areas such as the Northern Rockies and British Columbia will be changed less than smaller rivers draining from the warmer Cascade Mountains.

But even the Columbia River system upstream from The Dalles could have a 30 percent reduction in flow from snow pack.

Residents and industries likely will be faced with the choice of using water for summer and fall hydroelectric power or spring and summer releases for salmon runs, but not both, scientists concluded.

In the Yakima River Basin, the time for young fish to develop may be so short that some species of salmon may die off.

The river is likely to be warmer into the fall, when fall chinook need cool water to spawn. The fish won't enter the mouth of the Yakima until temperatures cool, said Lance Vail, senior research engineer at PNNL. The warm water also makes them more susceptible to disease.

With a late spawn, chinook won't hatch until later than they do now. Then with the spring freshet coming two months earlier than it does now, the salmon might not be mature enough to survive when the increased flows flush them downstream.

Reservoirs could be used to increase the spring runoff for species such as the fall chinook. But other species such as the bull trout in the Yakima system need a full, cold reservoir to thrive.

"Potentially what you do for one may not help others," Vail said.

The study also predicted problems for other areas of the West that could have California looking to water in the Columbia Basin system to ease its problems.

The Colorado River Reservoir System will not be able to meet all the demands placed on it, including water supply for Southern California and the inland Southwest -- because reservoir levels will be reduced by more than a third and releases by as much as 17 percent, the study predicted.

All users of the 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 impacts will be felt in reduced reliability of water supply and hydropower production. With less fresh water available, the Sacramento Delta could experience a dramatic increase in salinity, according to the study.

More accurate information about the effects of global warming still are needed, Pennell said. Models should improve over the next decade.

"If we obtain knowledge early enough to plan, we may be able to make the impacts less," he said.

Annette Cary
Warming May Hurt Salmon, Study Says
Tri-City Herald, November 11, 2002

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