As climate warms, what will our rivers do?

Fiona Cohen in the Seattle Post-Intelligencer: A team of University of Washington researchers is finishing the most detailed yet report what is likely to happen to Pacific Northwest rivers as the climate warms. The Columbia Basin Climate Change Scenarios Project predicts a shift in the landscape so great that engineers and planners are going to have to fundamentally change their methods of predicting what rivers are likely to do.

The usual method -- the one that people use to make decisions about buildings, roads, salmon, hydroelectric projects and water for agriculture -- analyses the historical data from river gauges. Alan Hamlet, a research assistant professor at the University of Washington's Department of Civil and Environmental Engineering, and the lead researcher on the project, says this method makes sense only if the climate isn't changing.

…So Hamlet, Eric Salathe, a senior climate researcher with the University of Washington' Climate Impacts Group, and a team of researchers set about showing the implications for different climate scenarios on 297 river gauges in Washington, Oregon, British Columbia, Idaho, Montana and Wyoming. They used 20 different climate models to generate temperature and precipitation projections for different watersheds. All of them show changes.

Predictions varied depending on the model, but it was clear that looking at history is no longer the best way to predict what happens to local rivers, Salathe said. "It's clear that it will change."

Rivers on the west slope of the Cascades will have more rain in the winter, and floods will be bigger and more frequent. For example, historical data at the Snohomish River near Monroe show two peak flow times: one during winter rains and the other during spring snow melts. With climate change, the river transforms. By the 2020s, winter flows peak at around 20 percent higher than the snowmelt season, the snowmelt season moves earlier, and summer flows dwindle….

Boats docked in Everett, Washington, on the Snohomish River, shot by Joe Mabel, Wikimedia Commons, under the Creative Commons Attribution ShareAlike 3.0 License