How and Why the LA Wildfires Grew So Fast—and Lessons for the Future
CAS Earth and environment professor explains how high winds and drought, combined with climate change, created a perfect storm

A search and rescue crew member sifts through the rubble of a recent fire. Photo by Richard Vogel/AP Photo
How and Why the LA Wildfires Grew So Fast—and Lessons for the Future
CAS Earth and environment professor explains how high winds and drought, combined with climate change, created a perfect storm
As Los Angeles starts to recover from the catastrophic losses from their deadly wildfires—which so far have killed 25 people, displaced 100,000, and caused tens of billions of dollars in damages—many wonder what first sparked the fires.

While officials investigate possible causes, including arson, sparking power lines, and errant fireworks, an expert told NBC News that natural causes are more plausible than arson, due to heavy wind conditions. No matter the cause, scientists say that the weather and climate conditions when the fires started January 7 created a recipe for disaster for the swift spread of the flames. Continued strong winds have kept the country’s second-largest city by population at risk for further calamity.
BU Today spoke with David Demeritt, a College of Arts & Sciences professor of Earth and environment. Demeritt is a geographer whose research focuses on environmental policy, especially the management of flooding, wildfire, and other environmental risks. Before joining BU in 2023, he taught at King’s College London for over 20 years and is a member of the Peer Review Colleges for both the Natural Environment Research Council and the Economic and Social Research Council. Demeritt is also an elected fellow of the Academy of Social Sciences.
Q&A
with David Demeritt
BU Today: Why have these Los Angeles fires spread so fast and ferociously?
Demeritt: The answer to this question depends partly on whether you look at the immediate proximate cause (high “Santa Ana winds” and drought) or longer-term trends in ecology, fire suppression, and land use.
In the first instance, LA is experiencing a climatological phenomenon called “Santa Ana winds” that leads to strong and very dry winds that create dangerous fire weather conditions. This happens regularly in Southern California in the late autumn and winter, driven by high pressure over the interior and temperature gradients (between Southern California’s comparatively warm coast and much cooler areas of high desert at higher elevations in Nevada and Utah), which create strong and very dry winds that blow out of the mountains and towards the warmer coast. These winds are further accelerated by the topography of the narrow mountain valleys leading down to LA and the coast. High Santa Ana winds fuel any ignitions, making them burn hotter, spread faster and farther, and greatly complicate fire suppression efforts, since it’s hard to deploy air assets like tanker planes and helicopters to spread water and fire retardant.
In these conditions, the Eaton fire burning the San Gabriel Mountains east of Pasadena reportedly grew twentyfold in size within hours, according to the New York Times.
This is possible because the vegetation is exceedingly dry. The last even moderate (less than a quarter inch) rainfall recorded at LAX airport was in April 2024. Since then, precipitation was recorded at LAX on just five other dates, totaling a meager 0.15”. The landscape is tinder dry, and so any ignition source, whether from errant cigarette butts or sparks from power lines blown over in the strong winds, is much more likely to take hold and spread.
BU Today: How do the dry conditions make the problem worse?
Demeritt: There is a lot of fuel on the landscape to burn. This time last year, Los Angeles was plagued with flooding (and landslides) that broke an extended long-term drought across the region. That burst of moisture led to plant growth, which has been steadily drying over the past year of very dry conditions.
What’s more, much of the vegetation in Southern California is fire-dependent shrubland called “chaparral,” which has not evolved to tolerate periodic burning. Fire is a regular part of the life cycle required by many species for their reproduction. But a long-standing US government policy of fire suppression has led to dangerous accumulations of fuel so that when the landscape catches fire, there is so much fuel that fires burn with greater intensity than they would have if we hadn’t had decades of active fire suppression.
While there is now expert consensus on the need to reintroduce fire to such fire-dependent landscapes, that is difficult because there is now extensive development in the so-called “wildland-urban interface”: building homes up against the mountains. Residents understandably fear prescribed burnings might harm their homes, but without burning—or other, more labor-intensive forms of fuel load management—the risk just increases year on year, so that when you do get a fire, it’s an inferno. Climate change means that the window for safe prescribed burning is narrower than ever before.
BU Today: How are these fires different from previous fires?
It’s important to recognize several things about the current fires in LA that make them different from past fire disasters in California. First, this is happening in the winter (because of Santa Ana winds), rather than in the more typical fire season in the West, which is during the late summer, when high temperatures and dry conditions raise the risk of ignition from dry lightning and increase the probability that any ignition will catch hold and be difficult to put out.
Second, while some of the fires in Los Angeles County, like the Kenneth fire in the wildland, have their primary fuel source coming from the vegetation that sends out embers affecting isolated homes—something on which my BU colleague Ian Sue Wing [a CAS professor of Earth and environment] has done some cool econometric modeling—the Palisades fire, in particular, has become an urban conflagration in which much of the fuel is provided by buildings. So it is not clear that trimming the vegetation to manage fuel loads on the landscape is going to mitigate the risk all that much.
BU Today: To what degree is climate change responsible for these fires?
It doesn’t help, but attribution is tricky. All of the [preceding] climate events—heavy rainfall stimulating vegetation growth, drought, Santa Ana winds—occur “naturally.” And, as I said before, a history of fire suppression and the ignition risk posed by aboveground electrical wires also play an important role both in triggering this event and magnifying its severity.
Focusing on climate change leads to a certain kind of paralysis insofar as it suggests that unless we get the entire planet on board to reduce emissions to minimize climate change, there is nothing we can do. There are lots of things that we can do to make disasters like this less likely and less severe, like managing fuel loads to lower the risk, preventing housing development in places that are prone to wildfire, improving building standards and materials to reduce structural ignitability, and getting homeowners and communities to do more to create defensible space around homes and housing developments. Also, addressing evacuation routes and improving preparedness, so that when fires do occur, people can get out safely and in a way that doesn’t impede fire suppression efforts by clogging the roads and putting people at risk of burning in their gridlocked cars.
BU Today: What lessons are we likely to take away from these fires?
It’s early days yet, and I’m not optimistic about the prospects for much rational deliberation in a society so badly polarised and in awe of social media algorithms that promote bat-[expletive] crazy conspiracy theories and outrage—particularly, but not exclusively, on the right.
The financial hit for the insurance industry is going to be huge. Nationwide the insurance industry has been struggling with losses from climate-related extreme events. Many were withdrawing from California. This will only accelerate that trend. The state runs an insurance scheme of last resort, but it’s expensive and will likely become even more so. That will have implications for housing markets both regionally and nationally.
By contrast, I expect the policy response will be slower and much less effective. I’d imagine that some of the emergency evacuation planning for Los Angeles will get updated, after a good bit of blame-gaming. Some of the evacuations were handled badly. There may also be some renewed emphasis on fuel load management. But California is already relatively proactive in that area (at least compared to other parts of the country), and the circumstances in Los Angeles and Ventura Counties—with lots of shrubland and mountains surrounding the second-biggest [network of urban communities] in the US—are relatively distinctive. It’s not clear that what you’d need to do in LA is all that transferable to other parts of the West.
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