A thinning snowpack due to climate change could alter streamflow patterns in rivers on the Olympic Peninsula, presenting adverse effects for fish, according to a new report from the University of Washington and Washington State University.
The report, which the Washington Department of Ecology published recently, summarized projected climate effects on streamflow and water temperature statewide, as well as barriers within Washington water law to potential responses in streamflow management.
The report used a new dataset for streamflow modeling developed by Bart Nijssen in UW Civil & Environmental Engineering, according to Crystal Raymond, a climate adaptation specialist with the University of Washington and an author of the report.
Jonathan Yoder, director of the state of Washington Water Research Center and another author of the report, said the report will contribute to the Department of Ecology’s awareness of climate impacts on streamflow.
Yoder said that while the science behind climate-induced snowpack decline isn’t new, the report provides a new level of geographic specificity for projected streamflow patterns.
Rivers on the Olympic Peninsula and the western slope of the Cascades, specifically, could experience more exaggerated flow patterns than in other parts of the state, like rivers in Central Washington, according to the report.
Streamflow is largely dependent on the kind of precipitation, Yoder said. He said snowpack is like a reservoir, storing solid water in the mountains until summer temperatures melt it downstream. That melting maintains healthy flows during the summer, when precipitation is minimal.
But warming temperatures are changing the type of precipitation falling in the mountains.
“It doesn’t take much warming to raise winter temperatures enough for winter precipitation to fall as rain, rather than snow, and runoff in the winter,” Raymond wrote in an email.
When precipitation falls as rain, it enters streams directly and washes out, raising peak flows during the rainy season. The report mapped projected changes in streamflows during peak flow events, which occur roughly every two years, finding that peak flow changes will be the largest in areas where temperatures are usually near freezing.
A rising snowline will result in bigger floods, the report says.
And when rainfall floods rivers, it means little is stored for the summer months. Low flows in Olympic Peninsula and Western Cascade rivers are expected to get even lower as snowpack declines, but that’s not necessarily the case statewide.
Rivers on the Olympic Peninsula drain in a radial pattern from a centralized — and isolated — pocket of mountains, which makes streamflow patterns different from other parts of the state, Yoder said. Much of the flow in the Columbia River, for example, comes from snowpack-heavy parts of Canada.
Exacerbations in both minimum and maximum flows pose a challenge for salmon, according to the report.
