New report outlines Puget Sound region’s future under climate change

Hannah Hickey UW News

The Puget Sound watershed — the area west of the Cascades Mountains that stretches from the state capitol up to the Canadian border — is warming. It also faces rising seas, heavier downpours, larger and more frequent floods, more sediment in its rivers, less snow, and hotter, drier summer streams.

A new report by the University of Washington synthesizes all the relevant research about the future of the Puget Sound region to paint a picture of what to expect in the coming decades, and how best to prepare for that future.

“When you look at the projected changes, it’s dramatic,” said lead author Guillaume Mauger, a research scientist at the UW Climate Impacts Group. “This report provides a single resource for people to look at what’s coming and think about how to adapt.”

Ten UW authors contributed to the report, which draws on published papers, agency studies and regional adaptation efforts now taking place. This first major update since 2005 includes new topics such as sediment transport and landslides, more details on salmon impacts, ocean acidification and flooding, and more specifics about how different parts of the region will change.

The report looks at all 12 major river systems that drain into Puget Sound and the Strait of Juan de Fuca, summarizing projected changes that affect humans and ecosystems. The report is aimed at policymakers, resource managers and the general public.

Projected changes include:

Average air temperatures in Puget Sound will rise by between 2.9 and 5.4 degrees Fahrenheit by the 2050s, for the most optimistic scenario of future greenhouse gas emissions

Ocean levels will rise by 4 to 56 inches by 2100, with the latest predictions offering more specifics on geographic variability and the effects of storm surges

Winter flooding will increase due to rising oceans, more winter precipitation falling as rain rather than snow, and more frequent and intense heavy rains

Landslide prediction requires more research, but more rain in the winter and more extreme heavy rain events are expected to increase the overall risk of landslides

Rivers are projected to carry more sediment downstream, as glaciers recede and expose loose material, and higher river flows and more intense rainfall will likely act to increase erosion. For example, sediment in the Skagit River is projected to more than double by the end of this century.

Peak river flows are projected to rise the most in places such as the Snohomish River that have a lot of area around the snowline, where warming will cause precipitation to shift from snow to rain

Warmer air, less meltwater and lower summer flows will combine to raise river temperatures in the summer, making many waterways less hospitable for salmon

Heat waves are expected to become more frequent. While smaller than the changes projected for Eastern Washington, recent UW research shows a bigger public-health risk west of the Cascades, where people are less prepared for the heat

Agriculture west of the Cascades is very diverse, and the effects of climate change on this region are understudied

Warmer oceans will likely favor more frequent toxic algae blooms

Increasing acidity of seawater will affect the shellfish industry, and may increase the toxicity of some algal blooms. Impacts on other marine life are not yet fully known.

The report also looks at how the community is beginning to respond. It cites two recent studies on how increased river flows will alter flood risks, one for the lower Snohomish River, from Monroe to the Sound, and the other for the lower Skagit River, from Mount Vernon to the Sound.

“It’s taking that next step, from numbers that give you an idea of what might happen, to numbers that give you the specific information that’s needed to plan for climate change,” Mauger said.

The report also includes examples of community adaptation, both in planning and in practice. In 2007, King County combined all its flood-control districts so the region could more effectively prepare for a future with increased flooding. As another example, the city of Anacortes considered both rising seas and heavier river sediment in designing its new water treatment plant that opened in 2013.

“In the same way that the science is very different from the last report, in 2005, I think the capacity and willingness to work on climate change is in a completely different place,” Mauger said.

The work was funded by the Puget Sound Institute at UW Tacoma, which is supported by the Puget Sound Partnership and the U.S. Environmental Protection Agency, and by the National Oceanic and Atmospheric Administration. Other partners are the Washington Department of Ecology and The Nature Conservancy.

Co-authors are Joe Casola, Ronda Strauch, Beth Curry, Brittany Jones, Harriet Morgan, Tania Busch Isaksen, Robert Norheim, Lara Whitely Binder, Meade Krosby and Amy Snover, all at the UW.

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For more information, contact Mauger at 206-685-0317 or gmauger@uw.edu.

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