SEATTLE — Winter temperatures in the Pacific Northwest will increase during the next several decades, and the best climate estimates show “this will be a different place,” according to Nicholas Bond, Washington state climatologist.
“We have to anticipate a range of outcomes. We might luck out and have just a few degrees more,” Bond told a Sept. 6 seminar on climate change sponsored by the University of Rhode Island’s Metcalf Institute.
Bond is a principal research scientist with the Joint Institute for the Study of the Atmosphere and Ocean at the University of Washington and an affiliate associate professor with the Department of Atmospheric Sciences.
He said the changes in annual precipitation in Oregon, Washington and Idaho will be diverse, and the seasonality of precipitation will likely change. Winters will be wetter and summers will probably be drier.
Climatologists’ projections — not predictions, he said — show small changes over the next decade, more by 2040 and still more by the end of the century. That trend reflects a consensus among researchers, but not a unanimous opinion.
Snowpack, so vital to the region, will show different trends at different intervals.
“Everything is local,” he said. “One size doesn’t fit all.”
Overall, the freezing level in the region’s mountains will rise, meaning more winter precipitation will fall as rain instead of snow. That will have major effects in the amount of runoff from the rain that falls during the winter and from snowmelt in the summer.
Ingrid Tohver, research scientist at UW’s Climate Impacts Group, cited two rivers as example.
The Chehalis River, in Western Washington, is fed primarily by rainfall, not by snowmelt, so it runs low in the summer. However, higher freezing levels in the Cascades will mean more instant winter runoff, meaning rivers like Central Washington’s Yakima, now largely fed by snowmelt, could also run low in summer, right when irrigators need water most.
Bond projected higher winter flows for major Pacific Northwest rivers and more winter floods. There may also be more extreme weather events in summer, “though we’re just starting to look at that,” he said.
Hotter summers will also affect evapotranspiration, the sum of evaporation and plant transpiration, which determines how much water is required for irrigation.
“It has gotten sunnier in Eastern Washington,” Bond said. “Why that is, you got me.”
Irrigation will require 3 to 4 more inches per summer that was needed a couple of decades ago, he said.
“We’re making better models, but they’re imperfect. There’s always a range of outcomes.”
John Fazio, senior systems analyst for the Pacific Northwest Power and Conservation Council, said “a lot of what-if studies” have looked at potential impacts of climate change on the region’s hydroelectric system.
Changing precipitation patterns would how river flows balance with power demands. More winter runoff would create a higher supply of electricity during a period of less demand. Conversely, less water would be available for energy generation during the summer, when demand is greater.
Further complicating energy demands would be a projected population change, as “climate refugees” seek relief from the heat farther south.
“We’d have to look for a way to make up those demands,” he said.