The blazes that raced across western Oregon this week could be the most unexpected element in a fire season that’s full of surprises: not just more wildfires, but wildfires in places that don’t usually burn.
The forests between Eugene and Portland haven’t experienced fires this severe in decades, experts say. What’s different this time is that exceptionally dry conditions, combined with unusually strong and hot east winds, have caused wildfires to spiral out of control, threatening neighborhoods that didn’t seem vulnerable until now.
“We’re seeing fires in places that we don’t normally see fires,” said Crystal A. Kolden, a professor of fire science at the University of California, Merced. “Normally it’s far too wet to burn.”
The fires in Oregon, which have led to the evacuation of hundreds of thousands of people and are approaching the Portland suburbs, stand out from what has already been an extraordinary fire season in the West, where global warming, land-use changes and fire management practices have combined to create a hellish mix of smoldering forests, charred homes and choking air.
Before this week, Oregon was grappling with a much more contained problem, a series of smaller fires on both sides of the Cascade Range, which divides the state between east and west.
Fires are common in the east, which is normally dry, according to Philip Mote, a climate scientist at Oregon State University. In some areas of eastern Oregon the “return period,” or length of time between major fires, is as little as 20 years, he said.
But the western slope of the Cascades, which catches most of the moisture that blows in from the Pacific Ocean, is normally wetter. “Out here, the return period can be hundreds of years,” he said.
That protective moisture has faded, in large part because climate change has altered precipitation and temperature patterns.
Tim Brown, director of the Western Regional Climate Center at the Desert Research Institute in Reno, Nevada, said the extreme warmth had caused vegetation to become exceptionally dry and to burn more readily. Temperature, humidity, wind and solar radiation combine to dry out brush and are the key elements for fire. “We call it evaporative demand,” he said. And in recent weeks, he added, “the west Cascades have been really dry from the evaporative demand.”