Related Articles
Wildfires aren’t just tearing through larger swaths of the American West. They’re spreading more quickly, too.
A team of researchers looked at NASA satellite data on 60,000 wildfires in the contiguous United States between 2001 and 2020. After classifying each blaze by the most it grew in a single day, the scientists found that these growth rates had increased over time in much of the West, and California in particular.
Their study, published Thursday in the journal Science, also found that the fastest-growing infernos were responsible for a huge share of the devastation. The speediest 2.7 percent of blazes accounted for almost 80 percent of structures destroyed, two-thirds of fatalities and more than 60 percent of the money spent on fire suppression, the researchers found.
When it comes to wildfire threats, “we’ve been so focused on size,” said Jennifer Balch, the study’s lead author and an associate professor of geography at the University of Colorado Boulder. “But what we really need to focus on is speed.”
She and her colleagues’ findings highlight a key fact about the West’s worsening wildfire problem: The blazes that are most ruinous to homes and communities aren’t always the ones that burn the biggest areas. Like last year’s deadly wildfire in Maui, for instance. Or the 2021 Marshall fire in Colorado.
Dr. Balch lived through that one. The flames raced through drought-stricken neighborhoods near Boulder with the help of 110-mile-per-hour winds. “At the end of the day, it was a very tiny fire,” she said. “Yet it burned through over 1,000 homes.”
The outsize harm from fast fires underscores the importance for communities of knowing how to evacuate quickly, said Jonathan Coop, a professor of environment and sustainability at Western Colorado University who was not involved in the study.
Many of today’s deadliest fires burn so ferociously that firefighters cannot do much in the moment but get out of the way, Dr. Coop said. “If we’re not prepared for them, they hit us and they hit us hard.”
Better early-warning systems would help, said Volker Radeloff, a professor of forest ecology at the University of Wisconsin-Madison who also did not work on the study. The 2018 Camp fire in Northern California burned through nearly 55,000 acres in less than 12 hours, leaving residents of the town of Paradise little time to get out.
“A lot of folks, they had gotten no warning whatsoever before they had to jump in their cars and start driving,” Dr. Radeloff said.
To study wildfire growth rates, Dr. Balch and her colleagues spent much of the past decade wrangling satellite readings into a giant catalog of 60,012 fires and their day-by-day movements.
Her team did not try to pin down what might explain the increases they observed in wildfires’ spread rates. But Dr. Balch has a guess: hotter, drier conditions.
“It takes just a little bit of warming to lead to a lot more burning,” she said.
Scientists point to several factors that are contributing to the recent increase in destructive wildfires in the West. More homes are being built in flammable areas. Some forests have become dense and overgrown, partly because of management practices that call for every fire, no matter how small, to be put out.
Human-caused warming is also exacerbating the threat. A study published this week in the journal Nature Climate Change found that greenhouse warming increased the amount of burned area in western North America and several other regions in recent decades, even after accounting for changes in land use and population density.
Continued warming, Dr. Coop said, could limit the effectiveness of practices, like thinning trees or clearing out dead vegetation with controlled burns, that are meant to reduce the risk of extreme wildfires.
“Understanding the limitations of fuel treatments as we enter this climate-amplified fire regime will be important,” he said.
Another pattern that Dr. Balch and her colleagues uncovered is that many of the nation’s fastest-growing wildfires in recent decades were not in California. And many were not forest fires.
Topping their list was the outbreak of grassland blazes that ripped across Oklahoma and Kansas in 2017. At its peak, it swelled by more than 520,000 acres in a day, according to the researchers’ data.
In a study last year, Dr. Radeloff and his colleagues found that in almost every year since 1990, grass and shrub fires burned more land in the United States than forest fires did. They also destroyed more homes.
The fastest-growing California fire that Dr. Balch and her colleagues identified was the August Complex blaze of 2020. That cluster grew by 115,000 acres in a day at its fastest and remains the state’s largest wildfire on record.
<
