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Science behind Western Washington wildfires and how climate change may play a role

Scientists are studying 2017's Norse Peak fire to learn more about how forests regenerate and the impacts of climate change to create more destructive fires.

GREENWATER, Wash. — As the National Interagency Fire Center continues to warn that Western Washington is at above normal risk for wildfire, scientists are already at work trying to learn more about the impact of climate change on big fires in westside forests that are different from most of the western United States.  

From the crest of the Cascade Mountains to the Pacific Coast, there have been 299 fires reported for Western Washington so far in 2019. Wildfire season officially starts on April 15, but the west side of the state already had 51 fires by then. 

Most of those fires were relatively small, the largest at 100 acres, but the warmest and driest part of the season is still to come. Western Washington can and has seen monstrous, intense and fast-moving wildfires — one which stood as the state record for more than a century. 

"The big fires that shape the landscape here in Western Washington are a little bit like earthquakes," says Josh Halofsky, a research scientist for the Washington Department of Natural Resources, the largest firefighting agency in the state. 

The biggest fires, like the 1902 Yacolt Burn in southwest Washington, don't come very frequently, but they are devastating. That fire complex was estimated at burning one million acres. At one point, the fire advanced 30 miles in 36 hours. Yacolt also stood as the state's largest fire for 112 years, until the 2014 Carlton Complex in eastern Washington. 

These are called "stand replacement fires" in Western Washington. The fire ecology of Eastern Washington has forest species like Ponderosa Pine that have adapted to a life of typically lower-intensity fires that usually don't kill the trees. But Western Washington wildfires could wipe out full forests, leaving bare dead trunks and even trees un-blackened by flames, yet killed by intense heat.   

But it's not just the mega-fires that worry DNR. There are smaller fires which also replace stands of trees.  

One such fire started in September 2017, the Norse Peak Fire north of Mount Rainier. It was sparked by lightning on the east slope of the Cascade Mountains, but quickly spread to the west side — and in total, burned more than 50,000 acres. 

Now sites within the Norse Peak Fire zone are being used as a scientific laboratory to study how forests grow back, and how climate change could impact the likelihood of more fires on the west side. 

"Fires on the west side of the Cascades are just a different animal than the ones we are more accustomed to on the east side," says Dan Donato, also a DNR research scientist. 

And it's that "different animal" aspect that makes large forest fires in Western Washington relatively uncommon, but devastating when they do ignite.  

First, it takes the drying of the late summer to create burnable "fuel" out of the huge amount of trees, brush and other plants that grow — plus low relative humidity, unlike the more typical winds blowing off the Pacific Ocean. There has to be a source of ignition, mostly likely to be human-caused. The last ingredient is a dry, hot wind from the east side of the state.   

"That's what we want to look at, change in the potential for getting that perfect set-up," says Crystal Raymond of the University of Washington's Climate Impacts Group.  

Raymond says there are already more high fire danger days than there used to be in Western Washington. But the unknown factor is what climate change does to those east winds. By using climate models that reach into our past, researchers are hoping to learn about the future. 

"We just don't know if they will become more frequent and more intense, or less frequent and less intense," says Halofsky. 

It's research that's important, says Raymond, "Have a better understanding of how climate change affects the potential for wildfires in western Washington and Northwest Oregon specifically." 

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