LA’s Palisades, Eaton and Hughes fires show a greater trend in wildfire rate

Fires are growing faster in the western United States. The fastest of them – called “fast fires” – often break out near cities and account for most structural wildfire damage according to researchers who analyzed over 60,000 fires from 2001 to 2020.

Fast-moving fires grow about 4,000 acres or more on their fastest day, at least two football fields a minute. This one-day growth threshold for a “rapid fire” is even higher in California at nearly four football fields per minute.

Humans and our infrastructure start almost all of the fires that threaten our homes. Exactly why fires grow fast is a developing area of ​​research, but weather and fuel conditions can fuel the speed.

Of the 20 fastest fires between 2001 and 2020, 16 destroyed structures, and all but one fire came within 2.5 miles of a property.

Although many fast fires start near populated areas, location alone does not determine whether a fire will be fast.

“There are probably hundreds, maybe thousands of fires around the Hollywood Hills every year. Most of those fires are able to be put out,” said Maxwell Cook, a research assistant at the Cooperative Institute for Research in Environmental Sciences and geography Ph.D. candidate at the University of Colorado Boulder.

A wildfire not only needs the first spark, but also the optimal fuel and weather. When an ignition overlaps with adverse conditions such as heat, drought and wind, fires can spread faster than firefighters can contain them.

In the case of the Los Angeles fires, a three-month drought dried out vegetation and buildings, creating piles of firewood. The seasonal high-speed winds blew embers to nearby fuel and made the pace of fire growth impossible to match.

“When fires move that fast, there’s often not much that can be done in terms of stopping the fire. It really becomes a situation of getting people out,” Cook said.

Scientists have observed an increase in human-caused fires and expect that pattern to continue as the population grows and more people move into wildlands. The conditions that lead to faster fires are also expected to worsen as the West gets warmer and drier in line with climate projections.

The type of vegetation in an area can determine how quickly a wildfire spreads. The majority of fast-moving fires burn through grasslands, where the short, dry grass is easily flammable. Deciduous forests tend to burn more slowly in part because of higher moisture levels in the vegetation. The fires in LA were different and spread by structure-to-structure ignition.

“When a house burns, it produces millions of embers and flames up to 5 meters (14 feet) high for an hour, which contributes to the burning of other houses,” said Guillermo Rein, professor of fire science at Imperial College London.

Housing density can work for or against firefighting and potential damage. Densely populated areas can often act as fuel breaks for a wildfire because they tend to have less flammable vegetation. However, they risk that one burning house threatens another. More remote areas do not have the same house-to-house risk but can be difficult for firefighters to reach.

“Pretty much every fire that starts in California is close to where a lot of people live,” Cook said. “It’s its own beast.”

The frequency and size of wildfires is well documented, but Cook and his team say fire rate measurements deserve more attention and are an integral part of assessing human safety in fire-prone areas.

“By incorporating understanding of fire speed into urban planning and into fire management, it will give you a much more nuanced understanding of what risk you’re actually taking on.”