As 2012 wildfire activity edges toward a record high, researchers say current fire levels, once considered high-end outliers, may soon be the new normal for much of the American West.
According to a recent analysis by the nonprofit research organization Climate Central, four decades of steady temperature increases correlate strongly with an increase in the prevalence of large fires, as well as an uptick in total annual acres burned.
"The research shows that when you have periods of high temperature and increased drought, you get big fire years. There's a clear link between change in climate and change in wildfires," said Jennifer Marlon, a postdoctoral fellow at the Yale School of Forestry and Environmental Studies, during a teleconference yesterday.
Record heat and drought this summer have exacerbated wildfires across the country, and in Western states in particular.
Currently, Wyoming, Idaho, Montana, Oregon and Washington contain the country's largest fires. Evacuations went into effect for several communities in Washington yesterday as fires burned through parts of the Okanogan-Wenatchee National Forest.
Firefighters see little relief on the horizon, with warm, dry conditions continuing across most of the West this week. Gusty winds across the Great Plains could hamper firefighting efforts in that region.
While Western states often see burns continue through September, large fires in the eastern part of the Rocky Mountains are unusual for this time of year, forest managers say. Montana, which usually sees its fire season end in mid-September with the state's first frost, is currently in the grip of five large fires, with rural structures threatened.
A longer, hotter fire season
Across the globe, temperature increases associated with climate change are expected to shift weather patterns in complex ways, bringing increased rainfall to some regions and greater aridity to others. Vegetation will likely spread in parts of South America while equatorial desert regions expand.
In the American West, however, the picture is far less complicated: Higher temperatures correlate with drier conditions and bigger, more dangerous fires.
Since 1970, spring and summer temperatures have increased more rapidly in the West than for the United States as a whole. Over the span of those 40 years, burn seasons have lengthened by almost two and a half months and the number of large fires -- those consuming more than 10,000 acres -- has increased sevenfold on Forest Service land.
On average, annual wildfires during the past decade burned twice as many acres as the fires of the 1970s.
As much as summer heat may play into the fire equation by priming fuels and hampering containment, however, the greater problem may be warming during winter months, said Steven Running, director of the Numerical Terradynamic Simulation Group at the University of Montana's College of Forestry.
"I think what we're seeing now in the northern Rockies is a consequence of a trend that starts with spring snowmelt," he said. "We're losing snowpack earlier, and that starts a summer dry-down of the entire landscape."
In the arid climate that dominates much of the West, summer rainfall is lost to evaporation before it can have an impact on the landscape's response to fire, he said.
When winter snowpack has been depleted, "the landscape just starts drying down relentlessly, starting from an earlier and earlier period," he added.