Speed Matters: Wildfires in Western U.S. Grow 250 Percent Faster Today Than Two Decades Ago

We generally discuss wildfires by their size: this many acres burned, this many structures affected. A study published Thursday in Science, though, argues that it’s the speed of a fire’s growth that really matters — and they’re getting much, much faster.

“Speed fundamentally dictates the deadly and destructive impact of megafires, rendering the prevailing paradigm that defines them by size inadequate,” wrote authors led by Jennifer Balch, a fire ecology expert at the University of Colorado. “The number of fast fire events that have destroyed >1000 homes in just the past 5 years is alarming and may foreshadow what is coming in years ahead.”

The authors examined the growth rates of nearly 60,000 fires between 2001 and 2020. In that period, the average peak daily growth rate more than doubled, with 2020’s rate at 249 percent of 2001’s. There have been some brutal examples of this in recent years: the 2018 camp fire, which burned an area almost four times the size of Manhattan on the day it began; the 2021 Marshall Fire, Colorado’s most destructive ever, fueled by 100 mile-per-hour winds; and the deadly Lahaina fire in Hawaii in 2023 (pictured above), which burned through the town in a matter of hours.

Over the two-decade study period, fires that grew more than 1,620 hectares (about 4,000 acres) in a single day accounted for 78 percent of the structures destroyed by all fires, and accounted for more than 60 percent of the costs of suppressing them. Thus this new class of fire, which the authors designate “fast fires,” is defined by both its physical behavior and its societal impact. There is also a clear link between growth rate of the fires and their final size.

The increased growth rates are likely due to warming trends along with some other human-caused problems, like land use and vegetation changes. And regardless of cause, it seems clear that fire preparedness needs at least somewhat of a shift in attitude.

“Current national fire risk models and planning efforts tend to focus on fire probability, intensity, or area burned rather than on fire speed and consequent settlement exposure or potential damage,” the authors wrote. “With warming temperatures increasing the likelihood of wildfires across the US, we would expect to see more fast fire events in the future.”