Communities across the US that were once considered beyond the reach of wildfires are now vulnerable to disaster. As fires increasingly spread deep into neighborhoods, researchers estimate roughly 115 million people – more than a third of the US population – live in areas that could host the next fire catastrophe.
The understanding that many more Americans are at risk of losing their homes to wildfires comes as the climate crisis turns up the dial on extreme weather, drought and heat. But it’s also the result of new research that has exposed deep and dangerous gaps in our understanding of the threat.
“The risks are more extensive than people think,” said Joe H Scott, the chief fire scientist at the wildfire risk research firm Pyrologix. Recent tragedies have added to grim examples of what’s possible when the right conditions align.
There was Lahaina in 2023, when a firestorm killed 102 people and turned the historic Maui town into smoldering ruins. In 2021, powerful gusts drove flames through suburbs of Boulder, Colorado, as the Marshall fire became the most destructive in state history. And, in January, 30 people were killed and homes on all sides of Los Angeles were flattened when the fierce Santa Ana winds rained embers across neighborhoods.
Key stakeholders – scientists, first responders and members of the insurance industry among them – are racing to understand the dynamics that drive these types of fires.
They’ve learned that flames enter and move through structures differently from when they burn through backcountry, complicating scientific models used for decades that showed wildfires fizzled out at the edges of neighborhoods. Realizing that homes themselves serve as fuel, they’re working to build new tools that will help at-risk residents adapt.
Still, a stark disconnect about who is vulnerable remains, researchers say. Many of the suburbs and cities hit hardest by wildfire in recent years were caught off-guard. Millions more across the country don’t know that they are at risk.
“It is obvious wildfire and wildland urban fire is increasing,” Scott said. “Fire reached all of those places and did really damaging stuff. What other places are like that? The answer is, almost anywhere.”
The watershed year of ‘oh, no’
Long before flames roared through Lahaina, near Boulder and into neighborhoods across Los Angeles, researchers knew the hazards were there.
But there were blind spots.
It was clear that homes nestled deep in forests or canyons were in danger, but not as clear about the towns and cities just beyond them. Then, the towns and cities started to burn.
“You can really trace it back to around 2017,” said David Acuna, a battalion chief at Cal Fire, California’s fire agency. It was the watershed year of “oh, no”, he added.
In the state of California alone, more than 10,000 homes were damaged or destroyed by fire. The Thomas fire, which raged through neighborhoods in Ventura county, consumed more than a thousand homes alone.
It was a record-setting fire in a record-setting year. And the records wouldn’t last long.
The following year, the Camp fire would wipe the town of Paradise from the map. The blaze claimed 85 lives, including many people who perished while they were rushing to escape. More than 18,800 structures were reduced to rubble.
Following those disasters, researchers intensified their efforts to try to understand the dynamic set of conditions that sent flames surging out of the wildland and into communities.
Meanwhile, the conditions – and the fires fed by them – were also changing.
In California and other states across the American west, a region always exposed to extremes, swings between intense periods of wetness and dryness became more intense. Strong rains spurred dense vegetation in spring, while spiking temperatures in summer parched the young plants and turned them to tinder.
In northern forests, centuries of fire suppression led to unhealthy overgrowth that helped create more catastrophic burns. To the south, meanwhile, too-frequent fires and long stretches of drought damaged native plants, leaving more landscapes open to the spread of invasive grasses that grew and dried quickly.
Fire season, which was once confined to a window during the year when the weather was hot and dry, now started earlier and lingered longer, ultimately stretching further into the winter and autumn months when strong winds tended to whip through the west.
“Climate change is giving fires more time, and giving them more time gives them more access to bad conditions,” Scott said.
Temperatures and low humidity, which used to calm after the sun went down, were now continuing into the night. When fires are given more time to spread, they grow exponentially, according to Scott: “If you give a fire 10% more time to grow, it doesn’t just get 10% bigger – it gets 20 or 30% bigger.”
A growing ‘wildland/urban interface’
Even with behemoth blazes on the rise, development into once-wild areas continued a steady march, lining once-rugged hillsides and valleys with flanks of homes. The outcome of both housing shortages and growing costs in cities, along with the pull of rural living, these communities can increasingly be seen across Los Angeles, scattered through Oregon, or in Texas ranges.
Many were built directly into the wildland, expanding the “wildland/urban interface”, a term used to describe areas where there was a high chance of direct impact from fires. The population living in these WUI zones roughly doubled from 1990 to 2010, according to a study published by Stanford University researchers in 2022.
The team of climate scientists, fire scientists and eco-hydrologists found that areas with the most rapidly rising risks were among the most popular: the numbers of people living in the highest-hazard regions grew by 160% during that decade.
More people residing in danger areas means more people who could be affected if a fire starts. More people also mean a greater chance for accidental ignitions that can turn into infernos. Utility lines that pop up alongside developments can malfunction during extreme weather events, lawnmowers can spark the grasses they are cutting, and cars and trucks increasingly start fires in the vegetation that lines roads.
A growing number of high-risk zones
While it’s part of the explanation of the US’s growing fire risk, the wildland/urban interface phenomenon isn’t the only one. It doesn’t capture the growing risks to neighborhoods not as rural or remote, neighborhoods where residents felt far away from hillsides, grasslands or forests, and safely guarded by blocks of sidewalks and shopping districts.
“I was not technically in a high-risk zone,” said Loretta Williams, an Altadena resident whose home was leveled during January’s Eaton fire in Los Angeles. She knows, because she was concerned when she bought her house back in 1999 and looked the zones up herself.
The diverse district, rich with historic landmarks and deep community ties, stood nestled against the San Gabriel mountains. Those closer to the hills understood the dangers, but even after multiple fires churned through vegetation along the slopes through the years, residents farther away were assured by the miles between the hills and their homes.
On the night Williams’s home burned, she recalled, it seemed as if catapults were launching fireballs from on high.
Her house was not in the WUI. It was in the ember zone.
“When you have a high wind blowing a fire, the fire is not on the ground, it is in the air,” said Hugh Safford, a fire ecologist at the University of California at Davis and a regional director for the California Fire Science Consortium. Embers can cast flames miles ahead of the fire front, “exploding the entire landscape at once as this whole thing rolls down the mountain”, he said.
In past years, scientists have come to agree that embers help push fire footprints over larger swaths of land, but they also pose particularly high risks to homes. Drips of fire can land in decorative landscaping, waft into uncovered air vents or settle on eaves, quickly turning a wildfire into an urban conflagration that sweeps from house to house.
In extreme cases, embers have been documented traveling more than 10 miles (17km). But typically encompassing a mile and a half, the ember zone significantly expands the range of danger into suburbs and cities alike. The homes that burned in Los Angeles last month were in the ember zone, according to maps created by the US Fire Administration that detail the threats. There are thousands more across the city that remain at risk; in Los Angeles county, there are close to 9,000 structures in the wildland area but 1.3m in the ember zone.
While wind can add erratic elements to a fire, carrying embers farther, parched plants also play a role.
“Dead fuels get turned into embers really easily,” Safford said.
Embers are just the beginning, though. Once they find their targets and begin to burn a structure, the flames are then more likely to spread from home to home, according to Dr Michael Gollner, associate professor of mechanical engineering at the University of California at Berkeley. In September last year, he and his team at the school’s Fire Research Lab released a new type of model that was the first to fully reflect how fire moves through structures.
The work has provided an important piece to a puzzle that has long eluded fire-response experts, who have had to rely on models that only capture fire behavior in wildland and not in developed areas.
It also builds on other models created to expand public understanding of the risks. The United States Forest Service, for example, has a tool that categorizes wildfire risk to communities with approximations of the ember zone.
On an interactive website, maps show risk to homes with an index of where wildfires are likely and where intensity will be high. Los Angeles, for example, has a very high risk of wildfires – higher than 98% of communities in the US – according to their model.
There are more than 1,100 communities in 32 states across the US with characteristics similar to those that burned in the LA fires, the data from their project shows – and they aren’t only in the west.
More than half with the highest potential for disaster are scattered in other regions, and Florida, Texas, Oklahoma and Alabama rank among the top 10 states facing high threats from urban fire catastrophes, according to a new analysis done by the research organization Headwaters Economics that used that data.
“People were surprised that fire got into those communities that have burned in recent years,” said Greg Dillon, director of the Fire Modeling Institute for the USFS. He worked with Scott to build the project and said of the devastating fires that burned homes in Hawaii and Colorado: “In hindsight, we can look back into our data and see we had predicted those places to have very high wildfire risk.”
Racing to learn how urban fires behave
Expanding the footprint of where the risks lie is just the beginning. Researchers are now working to learn how fires in urban centers behave – and how they can help residents prepare.
The Insurance Institute for Business and Home Safety, a non-profit research and communications organization funded by the insurance industry, started a 10-year project in 2018 to look at how wind-driven fires spread from building to building. Their research relies on observations straight from the source: they are burning structures down.
With large fans housed in air hangars, researchers are setting the conditions and testing materials. They are positioning structures at different proximities to find the sweet spots for spacing. Piece by piece, they are starting to puzzle together the recipes for resilience.
Already they have honed in on the series of attributes that often create catastrophes: drought conditions and winds gusting at least 20mph, densely packed structures with highly flammable exteriors, and a pathway of fuel for the fire – landscaping plants or fences that feed flames onto homes.
“When embers land around or on buildings, in the first few minutes after ignition the flame is a few inches tall,” said Dr Faraz Hedayati, the lead researcher for the project. With enough fuel, though, whether that’s a decorative bush, an open trash bin or a wood-shingled roof, the fire grows taller.
Higher flame lengths are harder to fight and can spread quickly, especially in windy conditions. Once the flame has gotten into or onto a structure, it almost always results in ruin. Ninety percent of structures built without fire-resistant materials will be fully destroyed after that point, according to their research.
They have also found that, once a structure is ablaze, others near it are in greater danger.
“Structure-to-structure ignition occurs a lot and [a lack of] space is the driver of that,” said Steve Hawks, the senior director for wildfire at IIBHS. Even the best fire-resistant materials on newer homes built to higher standards are vulnerable to sustained radiant heat when there’s less than 20ft (6 metres) of space.
In a dense neighborhood, where sheds, fences, shrubs and accessory dwelling unites (ADUs) are packed between homes, fires have plenty of fuel and can consume blocks at a time.
Often, when the fierce winds blow, several dynamics are happening at once: embers shower from above, starting fresh fires that sweep between structures on the ground.
That’s why, the experts say, limiting fuel for both forms of fire is essential to stopping spread. “Zone 0” instructs residents to remove anything burnable from within 5ft (1.5 metres) of a house.
Wood fences or trellises shouldn’t hug homes. Mulch must be cleared. Trees, plants and storage structures have to be set back, allowing enough space for an ember to snuff out before it’s given a chance to grow. Farther out from 5ft, vegetation should also be managed and spaced, with specific recommendations set for zone 1 (5-30ft) and zone 2 (30-100ft).
Firefighters rely on defensible space to stage their battles more safely and a slower-moving fire is far easier to extinguish.
Clearing the space could prove incredibly effective, but it’s a challenging change to implement. Beloved trees and plants may have to be culled from neighborhoods that pride themselves on landscaping. It may mean sacrificing shade in urban centers grappling with spiking temperatures in favor of protecting against ignitions.
For now, researchers are focused on providing as much information as possible to empower more people to make these decisions, from new models that can provide firefighters better intel while battling the flames, to tools communities can use to lessen their risk.
While large-scale fire disasters are still relatively rare, they are on the rise. There is more to learn, and even more to do. But armed with more insights, it may be possible to prepare for the fires of the future.
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The reporting in this article was made possible by support from the Institute for Journalism and Natural Resources
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The Guardian receives support for visual climate coverage from the Outrider Foundation. The Guardian’s coverage is editorially independent
