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Investigators are trying to determine what caused several wind-driven wildfires that have across the Los Angeles area in January 2025. Given the fires' locations, and , it's likely that utility infrastructure, other equipment or human activities were involved.

California's wildfires have become in recent years. Research my colleagues and shows U.S. wildfires are and three times more frequent than they were in the 1980s and '90s. Fast-moving fires have been particularly destructive, accounting for and 61% of suppression costs between 2001 and 2020.

Lightning strikes are a common cause of U.S. wildfires, but the that threaten communities are started by human activities.

A broken power line started the that destroyed the town of Lahaina, Hawaii. on the ground can spark fires. California's started when a man pushed a burning car into a ravine near Chico. The fire destroyed more than .

What makes these wildfires so destructive and difficult to contain?

The answer lies in a mix of wind speed, changing climate, the legacy of past land-management practices, and current human activities that are reshaping fire behavior and increasing the risk they pose.

Fire's perfect storm

Wildfires rely on three key elements to spread: conducive weather, dry fuel and an ignition source. Each of these factors has undergone pronounced changes in recent decades. While climate change sets the stage for larger and more intense fires, humans are actively fanning the flames.

Climate and weather

Extreme temperatures play a dangerous role in wildfires. Heat dries out vegetation, making it more flammable. Under these conditions, wildfires ignite more easily, spread faster and burn with greater intensity. In the western U.S., aridity attributed to climate change has of forestland that has burned since 1984.

Compounding the problem is the rapid rise in nighttime temperatures, . Nights, which used to offer a reprieve with cooler conditions and higher humidity, do so less often, allowing fires to continue raging without pause.

Finally, winds contribute to the rapid expansion, increased intensity and erratic behavior of wildfires. Wind gusts push heat and embers ahead of the fire front and can cause it to rapidly expand. They can also create spot fires in new locations. Additionally, winds enhance combustion by supplying more oxygen, which can make the fire more unpredictable and challenging to control. Usually driven by high winds, fast-moving fires have become .

Fuel

Fire is a natural process that has shaped ecosystems for . Indigenous people historically to manage landscapes and reduce fuel buildup. However, a century of fire suppression has allowed vast areas to accumulate dense fuels, priming them for larger and more intense wildfires.

Invasive species, , have exacerbated the issue by creating continuous fuel beds that accelerate fire spread, .

Additionally, human development in fire-prone regions, especially in the wildland-urban interface, where neighborhoods intermingle with forest and grassland vegetation, has introduced new, highly flammable fuels. Buildings, vehicles and infrastructure often ignite easily and burn hotter and faster than natural vegetation. These changes have , creating conditions conducive to more severe and harder-to-control wildfires.

Ignition

Lightning can ignite wildfires, but humans are responsible for an increasing share. From unattended campfires to arson or sparks from power lines, .

Human activities have not only , but they also have resulted in fires that pose a higher risk to people.

Lightning-started fires often coincide with storms that carry rain or higher humidity, which slows fires' spread. Human-started fires, however, typically —hotter temperatures, lower humidity and stronger winds. This leads to greater flame heights, faster spread in the critical early days before crews can respond, and more severe ecosystem effects, such as killing more trees and degrading the soil.

Human-ignited fires often occur in or near populated areas, where flammable structures and vegetation create even more hazardous conditions. Homes and the materials around them, such as wooden fences and porches, and send burning embers airborne, further spreading the flames.

As urban development expands into wildlands, the probability of human-started fires and the property potentially exposed to fire increase, creating a feedback loop of escalating wildfire risk.

Whiplash weather

A phenomenon known as , marked by unusually wet winters and springs followed by extreme summer heat, was especially pronounced in Southern California in recent years.

A wet spring in 2024 fostered vegetation growth, which then dried out under scorching summer temperatures, turning into highly combustible fuel. This cycle fueled some of the biggest fires of the 2024 season, several of which were started by humans.

That dryness continued in Southern California through the fall and into early winter, with very little rainfall. Soil moisture in the Los Angeles region was about 2% of historical levels for that time of year when the fires began on Jan. 7, 2025.

As the factors that can drive wildfires converge, the potential for increasingly severe wildfires looms ever larger. Severe fires also release from trees, vegetation and soils into the atmosphere, increasing greenhouse gas emissions and exacerbating climate change, contributing to more extreme fire seasons.

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