(Bloomberg) -- Increasingly fast-moving wildfires were responsible for nearly 80% of homes and other structures destroyed in conflagrations in the US over the past two decades, according to a first-of-its kind study.
The growth rate of the fastest wildfires — those that burn at least 4,000 acres (1,620 hectares) in a single day — increased 249% in the western US between 2001 and 2020. During that period, some 1.8 million structures nationwide were threatened by a fast-moving fire, researchers found.
They calculated burn rates by developing a database derived from NASA satellite records of more than 60,000 fires that burned across the US over 20 years. The scientists then analyzed more than 200 million property records to estimate the number of structures within 2.5 miles (4 kilometers) of a fast fire and reviewed data on fire-suppression efforts. The researchers determined that fast fires razed 80,700 structures and damaged 57,883 others. Fighting fast-moving wildfires cost $18.9 billion between 2001 and 2020.
Scientists have documented the role of climate change in the explosion of megafires that burn hundreds of thousands of acres annually. But its contribution to fast wildfires is less clear, said fire scientist Jennifer Balch, lead author of the paper published Thursday in the journal Science.
“What we do know is that it takes just a little bit of warming to lead to a lot more burning,” said Balch, an associate professor at the University of Colorado at Boulder. “As a function of that, we also expect that because of hotter and drier conditions, particularly in the West, we’re also seeing this increase in how fast fires are moving and growing.”
Strong winds have fueled these destructive wildfires, carrying embers that ignite home miles from the fire front. Winds that exceeded 100 miles per hour spread the 2021 Marshall Fire three miles in an hour, destroying more than 1,000 homes in Colorado. The 2023 Lahaina Fire incinerated the historic Hawaiian town in two hours, killing more than 100 people. In Paradise, California, more than 16,000 structures and 85 people were lost in the 2018 Camp Fire that burned 52,000 acres in a day.
Balch said the threat these fast-moving wildfires pose to people and property means that officials should concentrate less on the size of fires and more on their speed. “I think the big upshot here is to forget megafires and focus on fast fires,” she said. “We really need to define the problem around fast-moving events rather than big fires that are burning into the wildlands.”
That requires efforts to harden houses against wildfire, such as covering vents to prevent wind-blown embers from entering a home. California requires homeowners in high-risk fire areas to thin out vegetation within 5 feet to 100 feet of their dwellings. Forthcoming regulations will mandate the creation of ember-resistant zones by removing trees, shrubs and flammable material, such as wood fences and decks, within 5 feet of a home.
Such measures allow firefighters to spend more time extinguishing blazes rather than trying to save homes and evacuate residents, according to fire officials.
The study found that the western US, which has experienced extreme swings between drought and deluge in recent years, to be most vulnerable to fast fires. In California, for instance, wildfires became 398% faster between 2001 and 2020, according to the researchers.
“What we know is we can’t remove fire completely from our beautiful landscapes and people want to live in these landscapes in the West,” said Balch. “So what we need to do is prepare communities for the likelihood of fast-moving events where we expect them to happen.”
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