Oregon has a new climate threat: fires rage where they usually don’t burn

The wildfires that hit western Oregon this week may be the most unexpected element in the wildfire season, which is full of surprises: not only new wildfires, but wildfires in places that normally don’t burn.

The forests between Eugene and Portland have not experienced such severe fires in decades, experts say. What’s different this time around is that exceptionally dry conditions, coupled with unusually strong and hot easterly winds, have caused wildfires to spiral out of control, threatening areas that have not yet seemed vulnerable.

“We see fires in places we don’t normally see fires,” said Crystal A. Caulden, professor of fire science at the University of California, Merced. “It’s usually too wet to burn.”

The fires in Oregon, which have evacuated hundreds of thousands of people and are approaching the Portland suburbs, are different from what was already an unusual fire season in the West, when global warming, land-use changes and fire management practices have teamed up to create a hellish mixture of smoldering forests. charred houses and stifling air.

Until this week, Oregon has been grappling with a much more subdued problem – a series of small fires on both sides of the Cascade Range, which separates the state into east and west.

Fires are common in the east, where it is usually dry, according to Philip Mote, a climatologist at Oregon State University. In some parts of eastern Oregon, he says, the “recurrence period”, or the time between major fires, is only 20 years.

But the western slope of the Cascades, which traps most of the moisture from the Pacific Ocean, is usually more humid. “Here, the return period can be hundreds of years,” he said.

This protective moisture has disappeared in large part because climate change has altered rainfall patterns and temperatures.

Tim Brown, director of the Western Regional Climate Center at the Institute for Desert Research in Reno, Nevada, said the excessive heat caused vegetation to be exceptionally dry and more prone to burning. Temperature, humidity, wind and solar radiation dry out the brush and are key elements of fire. “We call this evaporative demand,” he said. And in recent weeks, he added, “the western cascades have been really dry due to the need for evaporation.”

These dry conditions are likely to have been exacerbated by climate change, according to Meg Kravchuk, a professor at the Oregon College of Forestry. They “prepared the landscape” for the wildfire, she said.

The critical moment came on Monday and Tuesday, when a storm blew hot air from the high desert in eastern Oregon over the mountains, quickly spreading fires to the more densely populated western part of the state, according to Josh Clarke, a fire meteorologist with the Washington State Department of Natural Resources.

Those winds were the strongest the state has seen in at least 30 years, Clark said. And when they crossed the mountains, the winds swept through the river canyons, compressed the air, warming it even more and pushing it westward like fur.

As these fires raced westward, they encountered unusually dry conditions, which in turn allowed the already burning fires to spread quickly, Dr. “Fire can move very quickly and just explode in these canyons,” she said.

The wildfires threatening Oregon’s cities could be worse than anything else in this part of the state in decades, according to Cassandra Moseley, chief research fellow at the University of Oregon and professor at the Sustainable Environment Institute.

Tillamook, the series of fires that began in 1933 and destroyed hundreds of thousands of acres of land, was probably as bad as the fires this week, according to Dr. Moseley. According to her, it is difficult to say for sure, because “there is no one alive who could tell this story.”

And what has changed this time, Dr. Moseley said, is that 90 years ago, there were far fewer people living in these areas. “There were no people in Tillamook,” she said. By comparison, the fires this week are likely to result in a large number of casualties.

Already several mountain settlements have been destroyed by flames that swept through the surrounding forests. Government officials received reports of dozens of missing persons. And as some of the biggest fires approached the southern suburbs of Portland, authorities warned residents who thought to stay in some communities that there would be no firefighters to protect them.

The lesson this week is that the state must now prepare for the same, said Dr. Mote, an Oregon climate scientist, who recalled that extreme heat also led to record low snow cover in 2015.

“The big fires situation and the little snow year is what my colleagues and I, who have studied climate change in Oregon for 20 years, said they will happen over time,” he said. “And now they’re happening.”