Even the wetter forests of WA could see more wildfire, study shows

The forests of the Pacific Northwest, soaked in up to feet of rainfall each year, are known for growing some of the largest trees in the world. Together, they store thousands of tons of carbon dioxide in their trunks and support hundreds of critters.

But even these lush forests can be affected by climate change.

If the world continues to emit greenhouse gases at its current pace, the North Cascades, Olympic Mountains, Puget Sound lowlands and the Western Oregon Cascades could see at least twice as much fire activity in the 30 years following 2035, according to new research led by Alex Dye, a faculty research associate in the Oregon State University College of Forestry.

Fire seasons — the dry and hot months — are expected to get longer, in some places spanning from early spring to late into the fall. This increases the probability of a fire sparking in the coolest, wettest parts of the west, and introduces risks for electricity managers who harness hydropower from the veins of water that course through these forests.

The new research aims to better describe how climate change is impacting a region where fire was historically infrequent, west of the Cascade crest.

The Westside Fire and Climate Adaptation Research Initiative is a collaboration among academics from Washington and Oregon, the Washington state Department of Natural Resources and others led by the U.S. Forest Service. The research provided by the initiative is shared with the region’s large utilities, like Seattle City Light, and helps inform state and federal fire management.

“These sort of wet rainforests-like forests have the potential to reinforce this image, that it’s a low fire risk area,” Dye said in an interview, “especially in direct comparison to a lot of the drier and hotter environments throughout the U.S. However, with fires in the Olympics last year, and really throughout the west side, it’s part of something that’s been here for hundreds of years.”

Now it’s becoming more common. For the first time on record last year, more fires sparked in Western Washington than in Central and Eastern Washington combined.

Researchers looked at Remote Automatic Weather Station data from 1992 to 2020 across five pyromes, or regions with a shared fire regime. The pyromes studied included the Olympics and Puget Lowlands, North Cascades, West Cascades, as well as the Oregon West Cascades and Oregon Coast Range. At the locations of each weather station, researchers pulled climate data from a dozen global climate modeling systems under a high greenhouse gas emissions scenario.

By the mid-21st century, the research projects fire seasons will get longer across all regions. In the Olympics, the biggest shift will be the size and number of fires earlier in the year, from spring to mid-summer. The North Cascades could see big changes in fire risk from April through October, with small increases in March and November, according to the paper published in February in JGR Biogeosciences.

In the West Cascades, the models taken together projected larger and more frequent fires in early spring, but declines in all other months, including the summer and fall; however some individual climate models project much more extreme increases.

In the Oregon Coast Range, the models projected increases in the size of fires in July, and more frequent but smaller fires projected in May, June, and late summer. The Oregon West Cascades, under the modeling, could have more frequent fires across all months, although these fires were smaller than observed in the historical record during the late summer months of August and September.

The Olympics and Puget Lowlands, where the average “fire rotation” in the past 30 years was estimated to be more than 11,000 years, may see a four-fold increase in fire activity from 2035 to 2064, according to the research.

A fire rotation is the amount of time it takes for fire to burn an area equal to the entire landscape. That doesn’t mean every acre burns and some areas may burn more than once.

The North Cascades could see more than three times as much fire activity from 2035 to 2064, and the West Cascades could see nearly double, according to the paper.

The global climate models make projections of climate change that take into account all aspects of the atmosphere and earth, Dye said. The researchers chose 12 of them that would represent the spectrum from the extreme upper end to the lower end to somewhere in the middle in terms of changes in climate, specifically temperature and humidity and precipitation.

The models are not saying: This is what’s going to happen in 30 years, Dye continued; it’s a really complicated and difficult thing to project that far into the future.

“The general trends are entirely consistent with what we’ve known, and that’s that climate change will result in an increase in area burned,” said Joshua Halofsky, natural resource scientist for the state Department of Natural Resources and a partner in the Westside research initiative.

Warmer temperatures and drier air are likely to increase the window of opportunity for fire spread, making fire more likely to happen. But it’s not the end all be all. Climate is just one piece of the fire equation.

The research did not consider where the ignitions may be more likely to happen, nor account for changes in vegetation and fuels 30 years from now. It also didn’t consider where people are going to live in the future or how fire management might evolve.

Those are the basis of future research.

The Harvey Lab at the University of Washington is studying how previous forest practices and fires affect the future severity of fires.

“There isn’t really a lot of research on fuel treatments on the west side” of the Cascade crest, Halofsky said, “in part because of the rarity of these events until more recently.”

DNR is already tracking reductions in summer soil moisture in forests west of the Cascade crest, and in some cases pivoting to more drought tolerant native seed sources or species when they replant land that’s been logged or scorched in a fire, said Calvin Ohlson-Kiehn, silviculture program manager for DNR.

The agency is using about $13 million from the state’s carbon auction revenue to fund some of its work to adapt to climate change in Western Washington forests, like noxious weed control, non-commercial thinning, and restoration of U.S. Forest Service’s native seed orchards.

DNR is preparing to expand its nursery to raise more seedlings for reforestation.

“In 2020 and 2021, there were hundreds of thousands of forested acres that burned in Western Oregon and the impacts from that we felt at our state forest nursery here in Washington in Tumwater,” Ohlson-Kiehn said. “We literally received calls from landowners, large landowners trying to order tens of millions of seedlings, which we didn’t have.”

Today, the Skagit River, the largest Washington watershed draining into the Salish Sea, is fed by hundreds of diminished and disappearing glaciers in the North Cascades. It is the last river system in the Lower 48 to bolster all five Pacific salmon species, and steelhead, that still return here to spawn. It also supports Seattle City Light’s largest hydropower project.

As fire more frequently moves into the North Cascades, it has put both the hydropower and people at risk.

As a child, Upper Skagit Natural Resources Director Scott Schuyler, 60, rarely saw a smoky summer day. For his daughter, it was a part of the norm growing up in the foothills of the North Cascades.

The 2015 Goodell Creek fire quickly grew from a smolder to a blaze racing across the two-lane highway, and the Skagit River. It tore through more than 4,000 acres of dense coniferous forest near the Seattle City Light’s hydropower dams and two towns that house staff.

As Seattle City Light released its first wildfire risk reduction strategy last summer, the Sourdough Creek fire traced a similar path, scorching more than 7,000 acres including historic Upper Skagit village sites and their environmental and cultural resources, and leading the utility to shutter two of its three dams.

These fires have cost the utility more than $4 million, and that’s on top of costs of purchasing power generated elsewhere to replace losses during a low water year. City Light now manages its lands for fire and drought and it has hired a climate scientist to help map out a future with more heat, fire, and people, and less water.

“You just can’t ignore it,” Schuyler said, “when the skies are clouded over and the sun looks like an orange fireball. You can’t ignore the excessive temperatures we’re experiencing. We’re very alarmed — for the environment, for the salmon, for the creatures of the landscape, we’re worried about the future of water.”