Humans tripled length of wildfire season in US by sparking more than 800k blazes

Humans tripled length of wildfire season in US by sparking more than 800k blazes

27 February 2017

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USA –  Over the past decade, the United States has experienced increasingly intense wildfire seasons, especially in the west.

In California, for instance, there were nearly 7,000 wildfires last year, which collectively burned well over half a million acres of land, according to the state’s Department of Forestry and Fire Protection. Both the total number of California wildfires in 2016 and the overall area burned by those fires were above long-term averages, showing that fires aren’t just becoming more frequent but also more severe. In fact, eight of the 20 most destructive wildfires in California history have occurred in the past 10 years.

In Oregon, meanwhile, the total number of acres burned in 2016 was actually well below average — but the number of human-caused fires skyrocketed. The Oregon Department of Forestry reports that more than 90 percent of the fires sparked last year were the result of human activities, which is nearly 25 percent more than average.

As it happens, Oregon is not alone in having experienced a much higher number of wildfires directly caused by people. In a study to be published this week in the Proceedings of the National Academy of Sciences (PNAS), a team of researchers led by scientists with the University of Colorado at Boulder and the University of Massachusetts Amherst detail their findings that suggest humans cause so many wildfires that they have drastically increased the length of the wildfire season in the U.S. in addition to the total area that is burned every year.

The researchers used the U.S. Forest Service Fire Program Analysis-Fire Occurrence Database to look at all wildfires between 1992 and 2012 for which a state or federal agency was required to respond, excluding prescribed burns and managed agricultural fires. The study states that human activities were responsible for sparking 840,000 blazes in the spring, fall and winter over that 21-year timeframe, which led to the annual fire season lasting three times as long.

Naturally ignited fires, or those conflagrations sparked by lightning, are mostly concentrated in the summer months, while human-caused fires are more evenly spread out across all four seasons, according to the study. The researchers found that humans created an average of 40,000 additional wildfires during the spring, fall, and winter every year during the study period — more than 35 times the number of fires started by lightning in those seasons.

In all, 84 percent of the 1.5 million total wildfires included in the study were caused by people, with lightning sparking the remainder of the blazes. Human-caused wildfires account for nearly half of the total acreage burned, per the study.

“Our results highlight the importance of considering where the ignitions that start wildfires come from, instead of focusing only on the fuel that carries fire or the weather that helps it spread,” Jennifer Balch, Director of the Earth Lab at CU Boulder and the lead author of the study, said in a statement. “Thanks to people, the wildfire season is almost year-round.”

In Balch’s home state of Colorado, 30 percent of wildfires between 1992 and 2012 were started by people, and they burned more than 1.2 million acres. Due to those manmade fires, the state’s fire season lasted, on average, 50 days longer than it would have based solely on lightning-sparked fires.

The U.S. has spent more than $2 billion annually in recent years to battle wildfires, Balch and her co-authors note. And while it’s clear that reining in human activities that lead to these blazes must clearly be part of the solution, Balch and her colleagues point out that the impacts of climate change must also be accounted for.

“These findings do not discount the ongoing role of climate change, but instead suggest we should be most concerned about where it overlaps with human impact,” Balch said. “Climate change is making our fields, forests and grasslands drier and hotter for longer periods, creating a greater window of opportunity for human-related ignitions to start wildfires.”

Bethany Bradley, an associate professor at University of Massachusetts Amherst and co-lead author of the study, added that, though the researchers found significant increases in the numbers of large fires started by human activities over the 21-year span, the effect was most pronounced in the spring. That finding, she said, could have serious implications as the effects of rising global temperatures continue to manifest: “I think that’s interesting, and scary, because it suggests that as spring seasons get warmer and earlier due to climate change, human ignitions are putting us at increasing risk of some of the largest, most damaging wildfires.”

Nonetheless, it is most certainly crucial that fire management policies take into account the dramatic impact on wildfire totals of human behavior, according to Balch.

“The hopeful news here is that we could, in theory, reduce human-started wildfires in the medium term,” she said. “But at the same time, we also need to focus on living more sustainably with fire by shifting the human contribution to ignitions to more controlled, well-managed burns.”

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