What happens when a wildfire reaches a city?

We’re making this story accessible to all readers as a public service. At Vox, our mission is to help everyone access essential information that empowers them. Support our journalism by becoming a member today.

Multiple major wildfires, fanned by unusually strong seasonal winds, are currently burning through the Los Angeles area, leaving devastation in their wake.

Thus far, those fires have led to at least five fatalities, massive evacuations, and significant damage to more than 2,000 buildings.

Though destructive fire seasons have become increasingly common in California, it’s still relatively rare to see a major urban area facing fires in the way Los Angeles now is. But as populations have grown in communities that are close to vegetation and open space, experts told Vox, the risks of wildfires moving into denser, urban areas has increased. That dynamic is compounded by climate change, which has fueled extreme heat and parched the landscape in regions like Southern California that are already susceptible to wildfires.

Collectively, these factors mean that wildfires may become more frequent in urban areas — and while cities do have some safeguards in place against these natural disasters, there are dangerous sources of fuel in them, too.

Urban fires “have become more common and severe,” says fire historian and Arizona State University professor emeritus Steve Pyne. “A problem that we thought we had fixed has returned.”

For places that are located near vegetation, as many parts of Los Angeles are, the fire risk can be high.

“In the Southern California urban areas … we see a highly dense, large urban area butting right up to highly flammable shrub ecosystems,” says Mark Schwartz, a University of California Davis conservation scientist.

These cities have sections that exist in what researchers call the wildland-urban interface, or WUI, where human development meets “undeveloped wildland” and vegetation. That means these populated areas are close to or intersect with natural ones like forests and grasslands.

Such adjacency to vegetation — especially in regions like the arid Western US, which is prone to fires — directly increases a city’s risk because blazes that typically begin in brush and shrubbery can move quickly through abundant fuel sources.

That danger is especially acute for Los Angeles right now, as Santa Ana wind gusts hit nearly 100 miles per hour — potentially carrying flames rapidly from where they begin.

In general, more people have also been moving into wildland-urban interface spaces, increasing the population and activity in these areas, says Noah Diffenbaugh, a climate scientist at Stanford University. That means more risk to humans living there, and also more potential for fires to start. While lightning strikes can and often do spark wildfires, most blazes are caused by people; past conflagrations have started because of campfires, an irresponsibly discarded cigarette, or downed power lines.

“Where there are humans, there’s plentiful sources of ignition, and where those sources of ignition are near vegetation that can burn, that elevates the risk,” Diffenbaugh said.

Climate change only amplifies such hazards: The clearest signal that climate change is influencing the severity of fires is the rising temperatures, which lead to more fuels, such as dry vegetation, that are primed to burn.

Cities that are more “hardscaped” (comprised of materials like concrete and metal) and farther from sources of vegetation have lower fire risk. Those that have greenery can also make themselves more fire resistant with mitigation practices like prescribed burns (controlled fires meant to simultaneously reduce fire risk and promote healthy vegetation growth), more native plants, and less vegetation near structures.

Homes, as well as vegetation, can serve as fuel for fires. Other structures like natural gas tanks and fuel depots can exacerbate blazes if they catch on fire, says Stephanie Pincetl, a University of California Los Angeles professor of environment and sustainability.

According to Schwartz, “Once a fire moves into an urban area, house to house ignitions becomes the biggest concern.” Homes built of wood can be flammable, and embers can also be blown into structures via vents and windows, so a house can catch fire and burn from the inside, even if the exterior is fire-proof. Free-standing single-family homes — compared to row homes, which often share walls with neighboring buildings — can be especially vulnerable to fires because of how many exterior-facing walls they have and the number of different points where a fire can catch, Pincetl notes.

In cities like Los Angeles, drier vegetation like palm trees can also provide fuel for wildfires.

The Camp Fire, which took place in northern central California in 2018, is the deadliest in state history. It caused 85 fatalities, destroyed more than 18,000 structures — including burning almost completely through the town of Paradise, California — and burned over 153,000 acres.

It was so destructive due to similar conditions we’re witnessing in Los Angeles County this week: “High winds piled on top of dry fuels,” Schwartz said, emphasizing that the wind played a particularly significant role in spreading the flames. As Wired’s Matt Simon explained, the wind during the Camp Fire helped carry “billions” of embers, which started a number of small fires farther from the front lines of the main blaze. Those embers ignited homes and other structures across Paradise — making the fire tougher to contain.

Many homes within Paradise were also more vulnerable to fire. Almost all the homes in town had been built prior to 2008, when California imposed a new fire-safe building code that requires the use of certain materials for building exteriors and roofs, the Los Angeles Times reported.

The leveling of Paradise was devastating: Before the fire, around 27,000 people lived in the community. As of 2023, its population was fewer than 10,000 (though it has continued to rebound since the fire). The fires burning in Los Angeles County threaten a far denser urban area: Today, almost 10 million people live in Los Angeles County.

Both wind and ample dry vegetation have also contributed to the growth of the recent Los Angeles fires, which have spread as the area has experienced both moderate drought conditions and a massive windstorm.

Experts say it’s “unlikely” that the current wildfires could damage all of Los Angeles due to both the diversity of landscapes in the city and the precautions that it — and other cities — have taken to strengthen firefighting forces and use more fire-resistant building materials such as plaster and concrete. “Cities used to be very, very flammable,” Pincetl said. “Over the decades, we have learned to build cities that are far less vulnerable to catching on fire.”

“It used to be back in the late 1800s, for example, that entire cities would be lost because everything was made out of the same wood material,” Tim Brown, a researcher at the Desert Research Institute, told Vox. “In today’s built environment, there are varying building materials, especially in urban and commercial centers, that would allow for much easier fire control.”