As the climate gets warmer, the old rules for when to let water out of Columbia Basin dams and when to hold it back won't work.

GRANTS PASS — As the climate gets warmer, the old rules for when to let water out of Columbia Basin dams and when to hold it back won't work.

So researchers from the University of Washington's Climate Impacts Group and the U.S. Army Corps of Engineers have developed computer models that simulate new operations schedules for flood control dams in Washington, Idaho, Montana and Canada based on a climate change scenario.

As the climate warms, there will be less snowpack and it will melt earlier, requiring different schedules to maximize dam operations, Alan Hamlet, a University of Washington research assistant professor in civil and environmental engineering, said Friday from Seattle.

"What the projections show for the Pacific Northwest is that as we warm, the region will tend to lose snowpack in the springtime," he said. "The result is river flows shift from summer to wintertime. You get an increase in winter flows, decreased and earlier peak (spring) flows and less flow in summertime. It is really coming from the fact there is less snow."

Dam operations are not being changed yet. But the simulations are showing how to make the dams better serve the needs of power generation, irrigation, salmon and recreation as the climate changes, said Carolyn Fitzgerald, chief of water management for the Corps of Engineers Seattle District.

"This is research that looks at whether this would be an effective way of dealing with potential changes in the runoff pattern," she said. "And the approach shows promise."

The simulations are based on long-term climate forecasts from the United Nations' Intergovernmental Panel on Climate Change, with a temperature increases of 3.6 degrees by 2050.

The current system is based on past flow patterns and short-term water forecasts.

The simulations look at major flood control dams high in the watershed, such as Grand Coulee Dam in Washington, and do not look at run-of-the-river dams on the lower Columbia, which have little capacity for flood control, Hamlet said. They work on an optimization principal that automatically adjusts for the changing climate.

"It's very complicated to rebalance this system," said Hamlet. "You can't do it by hand. That's why we developed this very sophisticated tool."