Vast Majority of Wildfires Caused by Humans

In an analysis of 20 years of wildfire records led by researchers at UMass Amherst and the University of Colorado-Boulder, they found human-started fires accounted for 84 percent of all wildfires, exhibiting ‘a remarkable influence’ on modern US wildfire regimes. Further, humans are expanding the fire niche into more locations and environments with historically low lightning-strike density.

(CN) – People cause 84 percent of all wildfires in the United States, according to new research that highlights the “remarkable influence” humans have on size and severity of these disasters.

The remaining 16 percent of blazes are caused by lightning, according to the new report, which analyzes the impact humans have on expanding the “fire niche” – a measure of ignition sources, dryness and fuel mass.

“Humans are expanding fires into more locations and environmental conditions than lightning is able to reach,” co-lead author Bethany Bradley said.

The team found that of the 1.5 million fires that required firefighting between 1992 and 2012, human-started blazes accounted for 44 percent of the area burned.

“It’s generally pretty well known that people start a lot of fires; everything from campfires to burning yard waste to accidental fires in homes and other structures,” Bradley said. “But in the past, I used to think of ‘wildfire’ as a process that was primarily natural and driven by lightning.

“From our analysis, we learned that human-started fires are amazingly common.”

Lightning-started fires primarily occur in the inter-mountain West and almost exclusively during the summer, Bradley said. Human-started fires, on the other hand, can happen anywhere in the United States, with a fire season that lasts from spring until fall.

“We saw significant increases in the number of large, human-started fires over time, especially in the spring,” Bradley said. “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.”

Co-lead author Jennifer Balch at the University of Colorado-Boulder pointed out that while human-started wildfires present a growing risk, broad lifestyle and consumption adjustments could limit their damage.

“The hopeful news here is that we could, in theory, reduce human-started wildfires in the medium term,” Balch 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.”

The team reviewed the publicly available U.S. Forest Service’s Fire Program Analysis-Fire-Occurrence Database, which includes federal, state and local wildfire records on private and public land. Fire causes include railroads, smoking, fireworks, arson and children, as well as burning debris and campfires. The researchers didn’t include agricultural fires or prescribed burns.

“Economic and ecological costs of wildfires in the United States have risen substantially in recent decades,” the team said. “While climate change has likely enabled a portion of the increase in wildfire activity, the direct role of people in increasing wildfire has been largely overlooked.”