The number of wildfires larger than a thousand acres has doubled across much of the West since the 1970s and the trend doesn’t show any signs of slowing, according to a new climate study.
Over the past decade, the average annual burn has been at least 2 million acres on U.S. Forest Service land, according to records studied by the research group Climate Central. That’s a scar the size of Yellowstone National Park. In addition, the West’s forest fire season has extended by 75 days compared to 40 years ago.
“We’re seeing a clear change, with bigger fires starting earlier, showing longer fire durations,” Jennifer Marlon of the Yale School of Forestry and Environmental Studies said in a conference call arranged by Climate Central. “The scientific community is actively searching the ‘why.’ But the mechanics connecting climates and fire are quite clear. Warmer temperatures, especially in the spring, lead to early snow melt, a wider window for fuels to dry out and a longer window for ignitions to start.”
“The Age of Western Wildfires” study published Tuesday reviews forest fire records of the past 42 years in 11 Western states, including Montana. It found that compared to the 1970s, there were seven times as many fires that burned at least 10,000 acres annually and five times as many that grew beyond 25,000 acres. Where the ’70s averaged fewer than 50 fires larger than 1,000 acres a year, those Western states had more than 100 on average between 2002 and 2011.
“The overall trend we should expect for coming decades is a slow but relentless trend of earlier snowmelt and more fires,” said University of Montana climate researcher Steve Running, who participated in a conference call about the report Tuesday. “I don’t think we want to overstate every single year will be like this into the future. But the probabilities will tilt for these to be more common than they have been in the past.”
Both Marlon and Running’s research was cited in the report, although it was authored by staff at Climate Central. The nonprofit organization is based in Princeton, N.J., and Palo Alto, Calif.
According to the latest version of the International Panel on Climate Change, summer temperatures could increase between 3.6 and 9 degrees in the Western United States by 2050. One result will be significantly earlier snowpack runoff, which triggers earlier fire seasons. The researchers claimed for every 1.8 degrees of temperature rise, the amount of land burned in forest fires could quadruple.
That will present challenges for future forest management. While Forest Service Region 1 Forester Faye Krueger recently stated the agency wants to build more resiliency to fire into the landscape, the researchers doubted such efforts would do much to bend the trend.
“It sounds odd to me to be able to fireproof landscapes,” Marlon said. “They are built to burn. They need to burn. Fires provide a cleaning, regenerative process. What’s needed is education about keeping defensible space around houses, and using proper building materials. We need to do a much better job of that, especially in fire-prone forests. You can’t fireproof the landscape.”
Marlon said more than a century of grazing and logging on public lands, combined with a long-standing policy of active fire suppression in the 20th century, has produced forests that contain historically large amounts of burnable fuel. Running added that the already dry Western climate leads to slow decomposition of dead and downed timber, compared to moister parts of the United States.
Running predicted that would lead to the Forest Service allowing more fires to burn in the backcountry.
“What they want to avoid are real holocausts, where everybody has to run for their lives,” he said. “We can’t stop these ignitions from starting. The only part of the fire equation we can have much chance to manipulate is the flammable fuel continuity on the landscape.”
But that also means places far from fire fronts will have to endure longer seasons of smoke-filled skies, the researchers agreed.
“Right now in Missoula, our visibility is maybe four or five miles,” Running said. “It’s Sept. 18, and historically this was the time of year we’d be getting our first frost of fall. Instead, we’re full into fire season. We’ve got fires going on all around us. The valleys are full of smoke, and the forecast for the next week is no relief in sight. It’s a clear illustration of the longer fire seasons we now have.”