The deadly wildfires sweeping across Los Angeles County have already claimed at least five lives, and forced tens of thousands of residents to evacuate — in some cases having to abandon their vehicles and flee on foot. So far, five active fires covering a total of more than 29,000 acres continue to burn, while firefighters struggle to contain the spreading flames. So, what will it take for these wildfires to stop? Rolling Stone spoke with two wildfire and climate experts and a meteorologist from the National Oceanic and Atmospheric Association (NOAA) to find out.
Why has the fire spread so quickly?
A combination of strong winds and extremely dry conditions has resulted in what Allison Santorelli, a meteorologist with NOAA’s Weather Prediction Center, refers to as “perfect fire weather.” Currently, there’s a sprawling area of high pressure over much of the Western U.S., plus strong winds across the Southern California area, she explains. “It’s really that combination of that high pressure — which is bringing in some stronger winds — and low relative humidity values,” Santorelli tells Rolling Stone.
How dry are we talking? According to the U.S. Drought Monitor, Southern California is experiencing a “severe drought.” On top of that, the area has also seen the strongest Santa Ana winds in a decade, says Craig B. Clements, PhD, professor of meteorology and climate science, and director of the Wildfire Interdisciplinary Research Center at San José State University. Santa Ana winds are powerful, dry, typically warm winds that flow east to west through Southern California’s mountain passages, according to the National Weather Service. They primarily occur from September through May, and because of their dryness and speed, also increase the risk of wildfires.
“If it was wet, then those winds would have maybe knocked down power lines, or caused some ignitions, but they wouldn’t have been catastrophic,” Clements says. Additionally, the fuel moisture content — or, the amount of water in vegetation and brush — in the Los Angeles basin is “below critical,” he notes. “L.A., because they’re in a drought, they didn’t get rain this season, [and] those fuels are primed,” he explains. “So that was what made this such a bad case.”
Why have the fires been so hard to contain?
The same winds responsible for spreading the fires are also making them harder to fight, Clements says. “It’s difficult when it’s so windy to get containment on these fires, particularly in this region, because they’re burning in such steep terrain, and there’s lots of complex wind turbulence in this area,” he explains.
The strong winds also make aerial firefighting more challenging. “For most big fires like this, they could drop a lot of water [on wildfires] with big aircraft and retardant,” Clememnts says. “But when it’s too windy, they can’t get the aircraft in.” That was a problem on Tuesday and Tuesday night, he notes. Aerial firefighting using both planes and helicopters will continue when the wind subsides.
To make matters even more complicated, Clements says, the wind has also been the driving force behind many spot fires, which occur when the wind carries an ember to a new location and starts a new blaze. “The winds are so high that they throw embers, then transport them so quickly, and those embers then ignite buildings,” he explains. “Embers get into buildings, they get into the eaves, they get into the vegetation surrounding the buildings, and then that house catches on fire. Now that house is starting to produce embers for the next building downwind. It’s this cascading event that continuously occurs.”
Finally, the fires have been particularly difficult to contain because of their location. “The area also has very complex terrain in the mountains and the valley,” says Tim Brown, PhD, research professor at the Desert Research Institute and director of the Western Regional Climate Center in Reno, Nevada. “It’s very abrupt changing landscapes, and that can help feed fires.” Plus, fighting these fires has required multiple strategies — some for traditional wildfires in forested areas, and others for the more densely populated neighborhoods that have been affected.
“This started as a wildfire, but it moved into a built environment,” Brown explains. “It started with extreme environmental conditions — the wind, the dryness — but then it moved to an area that is not fire resistant, with buildings that contain a lot of combustible material.” Once that happens, some people, including Brown, say it should no longer be called a “wildfire,” because it’s now an “urban conflagration,” moving from building to building. “It sounds subtle, but we think it’s an important distinction to try and get people to think about future mitigation,” he says.
What conditions are needed to stop the fires?
Ideally, it would rain, Clements says. Unfortunately, there isn’t any rainfall in the forecast for the next seven days in that area, according to Santorelli. “We’re not expecting any big rainfall events, or above-normal precipitation for this time of year, so we’re expecting that drought to continue, or possibly get worse,” she says.
That means it comes down to the wind. “What really needs to happen is the winds need to die down and cease blowing so hard,” Clements says. Indeed, wind speed is a major factor, according to Brown, who says that some stations have reported wind speeds near 100 m.p.h. this week.
A decrease in atmospheric pressure would also help. “Certainly you want some weakening of the pressure gradient there along the coast, which would help decrease the winds,” Santorelli says. “Some shift in the wind direction may bring in a little bit moister air.” But no major changes are expected over the next week. “There’s still going to be surface high pressure sprawled across the western U.S. here for the next seven days,” she says.
Though Santorelli expects the winds to subside at least a little by Friday, she says that there’s “still an elevated risk for fire weather that continues through the weekend.” There could be a brief uptick again in the wind across that area by early next week, but “not nearly as strong as what we’ve seen this week,” she notes.
