SALEM — The fires ravaging Oregon, called “unprecedented” by Gov. Kate Brown, have shown explosive growth and caused massive destruction because of a rare combination of factors: a powerful wind event uncommon at this time of year, forest management practices that have left forests overloaded with fuel, and a warming climate that has left that fuel exceedingly dry.
Many have unknown causes. Some may have been started by downed power lines, others by sparks from trailers dragging chains. It’s likely the causes for others will never be known. But the rare confluence of wind, fuel and heat have created a firestorm of blazes in the state that firefighters are struggling to keep up with.
And while they might easily be dismissed as a natural disaster, they are smudged with human fingerprints.
“Climate change is making fire circumstances like we’re seeing now more common,” said Erica Fleishman, director of the Oregon Climate Change Research Institute. “All the fire behavior we’re seeing is what has been projected by people who study climate change and its effects.”
Scientists have long predicted that, as greenhouse gases accumulate in the atmosphere, trapping heat and warming the climate, droughts would become more prevalent and more intense in the West. During the past century, most of the state has warmed by about 2 degrees, and the most recent analysis from the U.S. Drought Monitor showed more than 90% of Oregon is considered “abnormally dry.”
About 60% of the state, including most of the Willamette Valley, is considered to be in “severe drought.”
As temperatures creep up, Fleishman said, precipitation patterns change.
Water that would normally fall as snow comes down as rain, evaporating quickly or washing into rivers and the ocean, leading to diminished snowpacks. Those snowpacks act as a sort of reservoir, releasing water throughout the summer. Without them, less water is released onto the landscape in the summer months and forests dry out.
“Western Oregon entered the fire season with long-term drought after a poor showing of precipitation during winter/spring,” said John Abatzoglou, a professor at the University of California, Merced, who studies links between wildfire and climate change.
“Despite a healthy bump of precipitation in June, the last 60 to 80 days have been hot and dry, allowing fuels to dry out substantially and become receptive to igniting and carrying fire.”
The landscape on which those fuels sit looks different than it ever has in recent history, said John Bailey, a forestry professor at Oregon State University. Fire has always played a role in the natural cycle of forests, with low-intensity blazes burning through woodlands at regular intervals. That all began to change in the early 1900s, after a summer of massive blazes, when the federal government adopted a zero-tolerance policy for wildfires.
What would come to be known as the “10 a.m. rule” — which stated that fires should be contained by 10 a.m. the day after their initial report — resulted in decades of aggressive fire suppression, leaving forests without the naturally occurring burns that cleared out dry fuels and underbrush. Left unburnt, many forests across the Western United States now look as they never have before, brimming with fuel that has accumulated, in some spots, for more than 100 years.
“We’ve created whole new forest types that haven’t existed since the last glaciations,” Bailey said. “In the past it was much more fractured. We had grasslands that intersected forest and other things that interrupted that fuel matrix. Now there’s just fuel for miles and miles.”
It was against that backdrop that an unseasonal wind event barreled into the region on Sept. 7.
Last weekend, a large low pressure system dropped into the central U.S. and Colorado went from temperatures over 100 degrees Saturday to snow a few days later. That weather system pushed a front toward the West Coast, blowing dry air out of the northeast, over the Cascades.
“As the air moves down the mountainside it gets compressed and heats up,” said Briana Phillips, a meteorologist with the National Weather Service in Portland. “We were already in critical fire conditions. We were very dry. You couple that with strong winds, and we have this event.”
These kinds of winds are not uncommon, Phillips said, but they rarely blow through the region during the height of summer.
“We get east wind events in winter. That’s the time of year they happen,” she said. “But to have an east wind event during fire weather made this the historical event that it was.”
Gusts up to 50 mph blew through the Cascades like a bellows, accompanied by high temperatures and extremely low levels of humidity, fanning the flames of existing fires and turning new sparks into conflagrations within hours.
“Climate provides the setup,” Abatzoglou said, “but weather delivers the punch.”