Wildfires are gaining speed, a worrying trend for the US west

WASHINGTON – Increasingly fast-moving wildfires were responsible for nearly 80 per cent 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 1,620ha in a single day – increased 249 per cent 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 analysed more than 200 million property records to estimate the number of structures within 4km 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 US$18.9 billion (S$24.93 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 Associate Professor Jennifer Balch, lead author of the paper published on Oct 24 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 Assoc Prof Balch from 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 fuelled these destructive wildfires, carrying embers that ignite home miles from the fire front.

Winds that exceeded 161kmh spread the 2021 Marshall Fire 4.8km 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 21,000ha in a day.

Assoc Prof 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 mega fires 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 1.5m to 30.5m 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 1.5m 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 per cent 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 Assoc Prof Balch. “So what we need to do is prepare communities for the likelihood of fast-moving events where we expect them to happen.” BLOOMBERG