January 15, 2025
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Forest fires started by everyday human activities are often more destructive
Fast-moving wildfires, such as the one in the Los Angeles area recently, and started by humans, whether accidental or not, tend to be among the most destructive.
A fire engine crosses flames as it crosses Highway 36 near Paynes Creek as the Park Fire continues to burn in Tehama County, California on July 26, 2024.
Josh Edelson/AFP via Getty Images
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The conversationan online publication featuring the latest research.
Investigators are trying to determine what caused the various wind-driven fires destroyed thousands of homes throughout the Los Angeles area in January 2025. Given the locations of the fires, and absence of lightning at that timeutility infrastructure, other equipment or human activities are likely to be involved.
California fires have become more and more destructive in recent years Research my colleagues and I corrected It shows that they are fires in the US up to four times larger and three times more often than in the 1980s and 90s. Fast-moving fires have been particularly destructive as a result 78% of structures destroyed and 61% of removal costs between 2001 and 2020.
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Lightning is a common cause of fires in the US, though the majority of forest fires that threatened communities are initiated by human activities.
A broken power line started Deadly 2023 Maui Fire which destroyed the town of Lahaina, Hawaii. Dragging metal from cars or mowers can start fires on the ground. from California The biggest fire of 2024 it started when a man pushed a burning car into a ravine near Chico. It destroyed more than fire 700 homes and buildings.
What makes these fires 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 create.
A perfect storm of fire
Wildfires rely on three key elements to spread: good weather, dry fuel and an ignition source. Each of these factors has undergone significant changes in recent decades. As climate change sets the stage for larger and more intense wildfires, humans are actively fanning the flames.
Climate and weather
Extreme temperatures play a dangerous role in forest fires. The heat dries out the vegetation and makes it more flammable. In these conditions, forest fires start more easily, spread faster and burn more intensely. In the western US, there has been a drought attributed to climate change has doubled the amount Forest land burned since 1984.
Compounding the problem is the rapid rise in nighttime temperatures, today they rise faster than daytime temperatures. Nights, which offered respite with cooler conditions and higher humidity, do so less often, allowing the fires to continue to rage unabated.
Finally, wind contributes to the rapid spread, increased intensity and erratic behavior of fires. Gusts of wind push heat and embers ahead of the fire front and can cause it to spread quickly. They can also start fires in new places. Also, winds improve combustion by providing more oxygen, which can make fires more unpredictable and difficult to control. Normally driven by high winds, they have become fast-moving fires more often in recent decades.
the fuel
Fire is a natural process that has shaped ecosystems More than 420 million years. Historically indigenous peoples he used controlled burns to manage landscapes and reduce fuel accumulation. However, a century of firefighting the large area has allowed the accumulation of dense fuels, preparing for larger and more intense fires.
invasive species, such as certain herbshave compounded the problem by creating continuous fuel beds that accelerate fire spread, often doubling or tripling the activity of the fire.
Furthermore, human development in fire-prone regions, especially at the forest-urban interface, where suburbs intermingle with forest and grassland vegetation, has introduced highly flammable fuels. Buildings, vehicles and infrastructure often catch fire easily and burn hotter and faster than natural vegetation. They have had these changes has significantly changed fuel patternscreating conditions for more serious fires and more difficult to control.
turn on
Lightning can start fires, but humans are responsible for an increasing share of them. From uncontrolled campsites to sparks from power lines, More than 84% of fires affecting communities are started by humans.
Human activities are not alone It has tripled the length of the fire seasonbut they have also caused fires that are more dangerous for people.
Fires started by lightning often coincide with storms that bring rain or higher humidity, which slows the spread of fires. Human-caused fires, however, usually turn on in extreme conditions– warmer temperatures, lower humidity and stronger winds. This means higher fire heights, faster spread in the first critical days before crews can respond, and more severe ecosystem effects, such as more tree kills and soil degradation.
Human-caused fires often occur in or around populated areas, where flammable structures and vegetation create even more dangerous conditions. Houses and surrounding materials, such as wooden fences and porches, it can burn quicklyand sent the embers into the air, spreading the flames further.
As urban development it extends to the foreststhe likelihood of human-started fires and property exposed to fire increases, creating a feedback loop of increased fire risk.
Whiplash weather
a phenomenon known as bad weatherfollowed by unusually wet winters and springs and extremely hot summers, was particularly prominent in southern California in recent years.
A wet spring in 2024 promoted vegetation growth, which then dried out in hot summer temperatures, making it highly combustible. This cycle fed him Some of the biggest fires of the 2024 seasonmany of them started by humans.
This drought continued in Southern California through the fall and early winter, with little rain. It was soil moisture in the Los Angeles region about 2% of historical levels On January 7, 2025, the fires started for that time of year.
As the factors that can lead to wildfires converge, the potential for more and more severe fires increases. Serious fires are also released large amounts of carbon from trees, vegetation and soils into the atmosphere, increasing greenhouse gas emissions and exacerbating climate change by contributing to more severe fire seasons.
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