Willamette basin: Enough water for humans, but fish will suffer

Over the next 85 years, climate change will raise temperatures, reduce snowpack, and increase forest fires in the Willamette River basin. Population will double, and housing will replace farmland.

Does that mean we’ll run out of water?

Researchers have spent five years and $4.3 million examining that question.

On Friday, they presented their preliminary results: The news is good for humans, but not as rosy for native fish.

“The reason for optimism is the region’s 11 storage reservoirs coordinated by the Army Corps of Engineers that act as a valve for seasonal differences and preserve water for times of need,” said Anne Nolin, an OSU professor of environmental sciences and principal investigator on the study. “Without them, the picture would look quite a bit different.”

However, the Willamette River and its tributaries likely will warm enough to threaten cold-water fish species, including salmon and steelhead, the researchers said.

At the same time, an increase in river temperature would help warm-water and non-native species, such as common carp.

That could impact activities that are allowed on the river, such as industrial discharges or dam operations.

The researchers estimate that the Willamette River basin will warm between two and 13 degrees Fahrenheit by 2100, and that snowpack will decline from 63 percent of 95 percent lower than average.

Winters may be slightly wetter, but more of the precipitation will fall as rain instead of snow. Summers should be drier, meaning the area will rely heavily on water held behind the region’s 11 storage reservoirs.

“Unlike many parts of the country, those of us who live in the Willamette Valley are lucky because we have abundant water for human use, and we have institutional capacity to help mitigate water scarcity,” Nolin said. “However, the biggest negative impacts are likely to be for native cold-water fish and we will likely be facing a significant challenge in managing stream temperature for fish.”

The study, called Willamette Water 2100 Project, was funded by the National Science Foundation and led by Oregon State University in partnership with researchers from the University of Oregon, Portland State University and University of California at Santa Barbara.

tloew@statesmanjournal.com, (503) 399-6779 or follow at Twitter.com/Tracy_Loew