Why Does California Have So Many Fires?

California burns so often because it sits at the intersection of a fire-friendly climate, fire-adapted vegetation, over a century of fire suppression that loaded forests with fuel, and a rapidly expanding human footprint that both starts fires and puts more people in their path. No single factor explains the state’s fire problem. The combination is what makes California uniquely vulnerable, and climate change is tightening the screws on nearly every element at once.

A Climate Built for Burning

California’s Mediterranean climate is one of the driest in North America during its warmest months. Most of the state’s rain falls between November and March, leaving vegetation to bake through a long, dry summer and fall. By September or October, hillsides covered in shrubs and grasses have essentially become tinder. This seasonal drying is measured by something called vapor pressure deficit, or VPD, which captures how aggressively the atmosphere pulls moisture out of plants and soil. The higher the VPD, the drier the fuel. Research tracking California’s summer forest fires from 1972 to 2018 found that nearly all of the increase in burned area over that period could be attributed to rising VPD driven by warming temperatures.

On top of the seasonal drought cycle, California gets hammered by Santa Ana winds in the south and Diablo winds in the north. Santa Ana events push hot, dry air from the interior deserts westward toward the coast, sometimes gusting above freeway speed limits. Wind speeds on Santa Ana days with a large fire ignition average about 30 percent higher than on Santa Ana days without fires.¹ These winds do not just fan existing flames. They carry embers miles ahead of fire lines, making containment nearly impossible. The December 2017 Thomas Fire, for instance, coincided with a Santa Ana event that lasted 16 days and included four days of extreme winds, the highest number of extreme wind days in a 71-year record.²

What makes Santa Ana fires particularly dangerous is that wind speed alone does not determine whether a fire starts. The same study found that the majority of fires and area burned occurred during moderate winds, not extreme ones. The missing ingredient is an ignition source. On non-Santa Ana days, average wind speed is actually similar whether or not a large fire ignites. The wind creates the conditions; human activity or infrastructure failure typically provides the spark.

Climate Change Is Making Everything Worse

California has warmed by roughly 1.4°C during warm-season days since the early 1970s, and the relationship between that warming and summer forest-fire area is not linear. It is exponential, meaning each additional degree of warming does more damage than the last.³ Warmer air holds more moisture, which sounds like it might help. But when that moisture comes from the soil and plants rather than from rain, the result is drier fuel, not a wetter landscape. The atmospheric demand for moisture has climbed steadily, and projections show extreme fire weather becoming both more frequent and more widespread across California throughout this century.⁴

This trend interacts with natural climate oscillations that have governed fire patterns for centuries. Pacific and Atlantic ocean cycles, including El Niño–Southern Oscillation and the Pacific Decadal Oscillation, drive year-to-year and decade-to-decade swings in western wildfire activity.⁵ A wet El Niño year can grow extra grass that becomes extra fuel in the dry year that follows. Climate change is not replacing these cycles but intensifying the peaks. When natural variability lines up with the long-term warming trend, the result is a fire season that would have been almost unimaginable a generation ago.

A Century of Putting Out Every Fire

For most of the 20th century, the policy across California and the western United States was simple: suppress every fire as fast as possible. The logic seemed sound at the time. Fires destroy timber, threaten homes, and kill people. But many of California’s forests evolved with frequent, low-intensity fire. Those fires thinned out young trees, cleared underbrush, and recycled nutrients. Without them, forests grew dense and choked with fuel that would not have been there under natural conditions.

Research in mixed-conifer forests documented this shift decades ago. A hundred years of fire suppression shifted the composition of these forests, increased the density of small trees, and produced unnatural accumulations of ground fuels.⁶ The consequence is that when fires do break through suppression efforts, they burn hotter and more severely than they otherwise would. A 2024 study quantified this effect and found that maximum fire suppression increased fire severity by an amount equivalent to roughly a century of climate-change-driven drying or a century of additional fuel accumulation, each on their own.⁷ In other words, suppression did not eliminate fire risk. It stored it up and made the eventual fires far worse.

Comparisons with Baja California, just across the border, illustrate the point. In northern Baja, where fire suppression was minimal, fires burned more frequently under a wider range of weather conditions, preventing the kind of massive fuel buildup seen on the California side. In southern California, suppression reduced the total number of fires but increased the size of old-growth fuel patches, which meant that when fires did escape, they had more continuous fuel to burn through and were confined to rare episodes of extreme weather.

What Indigenous Burning Used to Do

Long before European colonization, California’s landscapes were shaped by deliberate burning. Indigenous communities used fire to manage food sources, clear trails, reduce pests, and maintain the mosaic of habitats they depended on. In the Karuk Aboriginal Territory alone, researchers estimated that pre-colonization cultural burning involved roughly 7,000 ignitions per year, averaging about six to seven ignitions per fire steward annually.⁸ Those ignitions differed substantially from contemporary fire patterns in both location and timing.

The scale of this burning matters because it shows that California’s pre-colonial ecosystems were not simply “natural” in the sense of being untouched. They were actively maintained by fire. When colonization suppressed both Indigenous people and their fire practices, the landscapes did not revert to some pristine baseline. They shifted toward denser, more fire-prone states that had not existed for thousands of years. Restoring some version of these burning practices is now recognized as part of the solution, though doing so at meaningful scale runs into regulatory, logistical, and political barriers.

Vegetation That Wants to Burn

Much of California’s landscape is covered in chaparral, a dense, woody shrubland that blankets hillsides across the southern part of the state and in coastal ranges. Chaparral species are not merely tolerant of fire. Many are adapted to regenerate after it, either by sprouting from root crowns or through seeds that germinate specifically in response to fire-related cues like heat and smoke.⁹ This means fire is baked into the ecology of the landscape itself. The vegetation grows back, accumulates fuel, and eventually burns again.

When fires return too frequently, though, even chaparral can be pushed past its recovery limits. Statewide analysis has shown that short-interval fire is the strongest driver of vegetation type conversion, where shrublands give way to grassy or herbaceous cover that burns even more easily. This conversion risk is highest where recurrent fire overlaps with warm-season aridity and proximity to human development, and lowest in cooler, wetter areas with longer intervals between fires.¹⁰ Once shrublands convert to grass, the landscape can enter a faster fire cycle that permanently changes the ecosystem.

Drought, Beetles, and Dead Trees

California’s multi-year droughts, particularly the severe 2012–2016 event, killed tens of millions of trees in the Sierra Nevada. Drought-stressed trees are easy prey for bark beetles, and the combination produced massive die-offs across frequent-fire-adapted forests. This mortality was not just a product of the drought itself but was compounded by the dense, overgrown conditions caused by decades of fire suppression.¹¹

Dead trees change fire behavior in stages. Initially, dead standing trees with dry needles increase the risk of crown fire. As those trees drop their needles and eventually fall, the risk shifts. Crown fire potential decreases, but surface fuel loads surge, increasing the potential for intense ground fires and heavy smoldering that produces massive emissions.¹² The scale of recent tree mortality is so large that researchers have warned of potential for “mass fire” events in coming decades, driven by the sheer amount and continuity of dry, combustible large woody material on the ground.

Analysis of specific fires in the Sierra Nevada confirmed that pre-fire tree mortality influenced wildfire severity, though weather still dominated. On one major fire, pre-fire mortality was the most important predictor of how much timber the fire killed. The effect plateaued at around 30 to 40 percent pre-fire mortality; beyond that level, additional dead trees did not increase severity further.¹³ This suggests there is a threshold beyond which the fuel load is already so high that more dead trees make little difference.

Building Into the Fire Zone

People keep moving into fire-prone areas of California, and this is one of the fastest-growing contributors to wildfire risk. The wildland-urban interface, where houses and vegetation mix, has expanded dramatically in California and globally. Worldwide, this zone grew by about 36 percent since 2000, with most of that growth happening between 2010 and 2020.¹⁴ California epitomizes this trend, with suburbs, exurbs, and rural homes pushing deeper into canyons and hillsides covered in flammable vegetation.

The consequences go beyond simply having more homes in harm’s way. More than three-quarters of California’s most extreme wildfires, measured by size, destruction, or deaths, started within about a kilometer of the wildland-urban interface. Climatic trends alone increased the frequency of high-risk fire weather about 2.5-fold from 1990 to 2022, but combining those trends with the expansion of human settlement into fire zones produced a 4.1-fold increase in conditions likely to produce extreme-impact wildfires.¹⁵ Climate and development are compounding each other.

Utility infrastructure adds another layer. Power lines, transformers, and other electrical equipment have been linked to some of California’s most devastating fires. Utility-related ignitions are a recognized source of catastrophic wildfire, first documented in Australia and southern California and increasingly common across the drought-stricken western United States.¹⁶ Modeling of electricity infrastructure fire risk in California found that weather features overwhelmingly dominated the risk predictions, eclipsing even factors like equipment age, pole material, and conductor design that one might expect to matter more.¹⁷ The takeaway is that even well-maintained infrastructure can fail catastrophically under the right weather conditions. This is why utilities now preemptively shut off power during high-wind events, a practice that was almost unheard of a decade ago.

Why Prescribed Burns Are Not Happening Fast Enough

If fire suppression created much of the problem, reintroducing fire through prescribed burns seems like an obvious solution. California’s land managers know this. The science is clear, and there is broad agreement that millions of acres need treatment. Yet prescribed burning remains far below what is needed, and the reasons are mostly logistical and regulatory rather than scientific.

Landowners trying to conduct burns face a thicket of obstacles. Limited funding, a shortage of experienced burn crews, narrow weather windows that comply with air-quality regulations, and complex environmental permitting all create a gap between what gets planned and what gets implemented.¹⁸ Air-quality rules are a particular sticking point. Prescribed burns produce smoke, and in a state with some of the nation’s strictest air-quality standards, burn windows shrink further. The irony is that uncontrolled wildfires produce far more smoke and far worse air quality than planned burns would, but the regulatory framework treats the two very differently.

Recent legislative changes in California have tried to reduce some of these barriers, including liability reforms that protect landowners who follow approved burn plans. But scaling prescribed fire to meet the need would require a cultural and institutional shift on par with the one that created the suppression-first policy in the early 1900s. Progress is happening, just not at the pace the fuel loads demand.

What the Smoke Does to People

California’s fires are not just a land management problem. They are a public health crisis. During the catastrophic 2020 fire season, direct fine-particulate emissions from wildfires spiked to 38 times above an average day. Air quality standards for fine particulates were exceeded by up to ten times in numerous locations, and wildfire smoke drove elevated ozone levels as well.¹⁹

The January 2025 fires in the Los Angeles area offered a striking example of how wind patterns shape who breathes the smoke. During that event, Santa Ana winds pushed peak hourly smoke concentrations above 250 micrograms per cubic meter near the fire but efficiently transported it offshore, causing those concentrations to drop to 60 micrograms within a day. Modeling estimated that the Santa Ana conditions actually reduced smoke-related acute deaths across major affected counties by about 60 percent compared to a non-Santa Ana scenario, because the wind blew smoke out to sea rather than letting it pool over populated areas.²⁰ But total particulate-related deaths still roughly doubled compared to the prior year, because the same Santa Ana winds carried background pollutants from inland sources into the coastal zone. The fires make the air dangerous, but the interplay between wind, geography, and existing pollution determines where that danger lands.

When the Carbon Math Breaks Down

California has tried to use its forests as climate solutions through a carbon offset program that lets polluters pay to preserve trees that sequester carbon. The idea depends on those forests staying intact. They have not. An analysis of the program’s buffer pool, a reserve fund set aside to cover losses from disturbances like wildfire, found it severely undercapitalized. Estimated carbon losses from wildfires within the program’s first decade depleted at least 95 percent of the contributions meant to protect against all fire risks over a hundred years.²¹ Even under the implausible assumption that no additional wildfires hit offset projects, the wildfire component of the buffer pool was forecast to be nearly drained by historical losses alone.

This matters beyond climate accounting. It reveals how deeply fire risk is embedded in California’s landscape and how badly institutions underestimated it. If a hundred-year reserve can be wiped out in ten years, the assumptions about fire frequency and severity that underpin housing, insurance, infrastructure, and conservation decisions are all miscalibrated. California does not just have a fire problem. It has a problem recognizing how big the fire problem actually is.