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Climate Computer Prognosticates on Columbia Basin's Watery Future

by Bill Rudolph
NW Fishletter, December 17, 2002

This fall's dry spell has the popular media full of global warming stories about ice sheets breaking up at the South Pole. But an Oak Ridge National Laboratory super-computer that has simulated the future Northwest climate predicts that 100 years from now, the Columbia River Basin will see just 3 percent less overall runoff than today. The big difference, will be a lot more rain and a lot less snow, according to the super-computer.

Such a future is the likely result of a degree or so (Centigrade) increase in temperature, due mainly to increases in greenhouse gases, said researchers from the University of Washington and other institutions. Such conditions will significantly affect hydro operations in the Northwest and make it more difficult to reach federal flow targets established to help migrating ESA-listed fish in the basin, according to the researchers.

The study, soon to be published in the journal Climatic Change, is part of a research initiative on accelerated climate prediction supported by the US Department of Energy, in concert with the Scripps Institute of Oceanography, US Geological Survey, Department of Defense and the Pacific Northwest National Laboratory.

The researchers, including UW civil engineering professor Dennis Lettenmaier, have published numerous studies that show small increases in temperature can substantially shift runoff patterns in the Columbia Basin. But they said their new model includes a "more realistic" coupling of the ocean, atmosphere and other features that allowed them to include decadal-scale climate effects in their assessment. Consequently, the new model predicts less warming than most other climate models because it includes a factor that stores more heat in the ocean.

"Other models show a much larger warming effect," Lettenmaier said. "However, even this 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."

Lettenmaier and his co-authors examined different policies for operating basin reservoirs to mitigate the predicted hydrologic shifts and found that a combination of earlier refill targets with greater storage allocations for fish flow targets could cancel most negative impacts, "but only with severe losses in firm hydropower production." They estimated such a power loss could be about 15 percent by 2050, but noted that revenue losses would be much less because power production would shift from summer and fall to winter and spring.

Not everyone agrees with this assessment. "It's a given that we can't meet existing flow targets anyway," said eastern Washington natural resources consultant Darryll Olsen. "What difference does it make?"

The climate study doesn't look at direct effects on fish, but is trying to simulate the way climate behaves, said Bill Pennell, director of the Atmospheric Science and Global Change Division at the PNW National Lab in Richland, WA. Three different runs were made to assess variability, Pennell said. Several other computer models were nested within the main model to add regional climate factors, hydrology, and the Columbia River hydro system.

He said the model doesn't mimic the climate phase we're in now, called the Pacific Decadal Oscillation. This 20- to 30-year cycle alternates between drier, warmer years with less productive ocean conditions and wetter, colder years that seem to go hand in hand with more productive ocean conditions. Most scientists think the region has now entered the wetter, colder cycle.

By the end of the century, flow deficits at McNary will be 40 percent greater than in control simulations without a 600-aMW reduction in firm power, the climate study said. It also predicted that average maximum flows at The Dalles will decline from about 550 kcfs (as recorded between 1950 and 1999) to about 450 kcfs by 2050, and to less than 400 kcfs by the 2090s. Snake River flows at Ice Harbor are estimated to decline from about 130 kcfs in June to maximum flows in early May of about 120 kcfs in 2050.

But the authors suggested changes in operations that could help meet competing demands of the hydro system in the dim future, without compromising flood control. By 2050 storage for fish flows will have to be almost doubled, to 4.3 MAF, to provide enough water to reach instream flow targets, they said. By the end of this century, storage would have to be increased by another 50 percent to satisfy flow targets.

The results of the modeling effort also showed a trend toward more extremes in climate on an annual basis, which the researchers said could lead to hydrologic "vulnerabilities beyond those revealed in results averaged over three decades." The report estimates future changes in time frames of 30 years' duration.

Does that mean the extremely dry fall in the Northwest is already acting like the model? Not likely, said UW climate researcher Nate Mantua. He believed the El Niņo conditions that have set in for the winter forced the high-pressure ridge into position off the coast, which had split the jet stream and caused most moisture-laden systems coming in from the Pacific to pass both to the north and south of the Northwest. "This El Niņo is a lot stronger than anybody predicted," Mantua said.

A recent forecast from the National Oceanic and Atmospheric Administration's Climate Prediction Center suggested that mature El Niņo conditions will be established by next February throughout the eastern Pacific Basin. "However," the Nov. 7 forecast said, "based on the latest predictions and an assessment of current oceanic and atmospheric conditions, we expect that this effect will be weaker than the 1997-1998 El Niņo. Warmer-than-average conditions are expected over the northern tier states, southern and southeast Alaska and western Canada throughout the winter." The Dec. 12 forecast said the drier-than-average conditions over the Northwest was an El-Nino related impact and to expect drier-than-average conditions over the northern tier states throughout the winter.

But local forecasters were right on the money when they called for plenty of rain by the end of last week, when the remnants of a tropical storm came ashore. However, the longer-range trend seems to be toward less-than-normal precipitation, with or without El Niņo. The latest word from the National Drought Mitigation Center says Boise, ID, is on pace to establish its driest calendar year on record in 2002. As of Dec. 3, year-to-date precipitation had totaled 4.93 inches, about 6.03 inches below normal. The lowest calendar-year precipitation total for Boise was set in 1966, at 6.64 inches. Normal December precipitation for Boise is 1.38 inches.

NOAA's Climate Prediction Center said the dry conditions aren't going to change anytime soon. In the Nov. 21 seasonal drought assessment, forecasters didn't sound optimistic and called for below-normal precipitation that should lead to continued drought for much of the inland Northwest, with dry conditions expanding northward to the Canadian border.

So far, the Columbia Basin above The Dalles has received only a little less than 60 percent of average precipitation for the past several months. The situation isn't any better on the Canadian side, which has received 57 percent.

"The real impact will be felt once melt occurs following the outlook period," said the forecasters. "Even above-average precipitation during the November-February outlook period will not guarantee that the seasonal snow pack in spring will be above average. Until we see what the seasonal totals will be, there is no guarantee that there will be improvement in water supplies."

Scientists are having a tough enough time figuring out what will happen 100 days from now, much less in 100 years, but that hasn't stopped a flood of speculation on the possible mechanisms that lead to climate change.

Academic papers published in the last two weeks speculate on variables that have not yet been included in any climate models. One asks whether the world's oceans are net sources or sinks of carbon. No one knows yet, but the answer could have huge ramifications for the greenhouse gas debate. Another group of scientists speculates in the latest Science magazine that cosmic rays, which vary in intensity during the 11-year solar cycle, may play a role in global cloudiness.

Bill Rudolph
Climate Computer Prognosticates on Columbia Basin's Watery Future
NW Fishletter, December 17, 2002

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