Humans have dramatically increased the extent and duration of wildfire season.

Wildfires cause more than $2 billion in damage each year. Photo by Bjorn Tore Okland via Unsplash

According to recent research from the University of Colorado Boulder, humans have dramatically increased the extent and duration of wildfire season.

It used to be that wildfires happened most often in the summer and tapered off dramatically after that. However, it now seems like wildfire season lasts the entire year, with fires being started in the spring, fall, and winter as well.

“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,” said study lead author Jennifer Balch, director of CU Boulder’s Earth Lab and an assistant professor in the Department of Geography. “Thanks to people, the wildfire season is almost year-round.”

The researchers studied 20 years’ worth of U.S. government agency wildfire records and found that human-ignited wildfires accounted for 84 percent of them. Nearly half the acreage burned over the average fire season was a result of human-ignited fires. In recent years, the annual cost of fighting wildfires in the U.S. has grown to more than $2 billion.

While summer fires are primarily caused by lightning strikes, human-ignited fires happen all year round, with significant increases especially noted in the spring.

“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,” said study co-lead author Bethany Bradley of the University of Massachusetts Amherst.

Although climate change is a very important factor in adding to the risk of wildfires, humans are clearly playing an increasing role in igniting the fires themselves. The most common day for human-started fires is July 4, U.S. Independence Day, most likely because so many people are using fireworks at their homes.

The new findings suggest that, since climate change is much harder to address on a local and regional level, the most important thing authorities can do to mitigate wildfire damage is to manage the human behavior element of wildfire ignition.

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