2024 has been a year of intense wildfire activity across the United States and North America, scorching millions of acres and disrupting communities from coast to coast. As the wildfire season winds down, now is the perfect time to answer the question of how wildfires start.
Wildfires are complex phenomena influenced by natural forces and human activities, from lightning strikes to land mismanagement. In this post, we’ll explore the science behind wildfire ignition, explore the role of human intervention, and outline the critical information needed to answer the most pressing questions about wildfire prevention and safety. This guide offers essential insights to keep you informed and prepared if you live in a wildfire-prone area or want to understand their causes and impacts.
How do wildfires spread?
Wildfires require three things to start—heat, fuel, and oxygen. Firefighters refer to this combination as the “Fire Triangle.” Heat is the primary catalyst, igniting the fire and continuing to drive its spread by preheating nearby fuels and removing moisture. While natural causes like lightning are common, human activity—such as discarded cigarettes or unattended campfires—is responsible for most wildfires. Fuel, which consists of any combustible material such as dry vegetation, trees, or fallen leaves, influences the rate at which a fire spreads. Drier fuels burn faster, and factors like fuel quantity, size, and distribution across the landscape further impact fire behavior. Proper fuel management, such as controlled burns or vegetation removal, can help reduce wildfire risk.
Oxygen, the third element, is abundant in the atmosphere and essential for sustaining a fire. While heat and fuel can be controlled to some degree, oxygen is uncontrollable, allowing wildfires to continue as long as it is available. The interaction between heat, fuel, and oxygen dictates how a wildfire ignites, spreads, and can be suppressed.
How fast do wildfires spread?
The speed at which wildfires spread can vary significantly depending on various factors, including the type of landscape, weather conditions, fuel availability, and terrain. Wildfires can move between 6 to 14 miles per hour on average, but this rate can escalate dramatically under certain conditions. Wind is one of the most influential factors in increasing wildfire speed. Strong winds can push flames forward, substantially expanding the fire’s reach. In fact, under extreme wind conditions, wildfires can race at speeds of up to 60 miles per hour, making them incredibly difficult to control and often overwhelming firefighting efforts, according to the National Fire Protection Association.
Other environmental factors also play a critical role in determining the pace of a wildfire’s spread. Drier ground fuels, such as dead vegetation, grasses, and leaves, allow fires to spread faster. Low humidity and high temperatures further exacerbate this by lowering the moisture content of the fuel, making it more flammable and allowing fires to burn hotter and longer. According to the U.S. Forest Service, in areas experiencing prolonged drought or high temperatures, fires can spread rapidly and consume more fuel, leading to larger and more intense wildfires. For example, the 2020 wildfire season in the Western U.S. saw flames in California, Oregon, and Washington moving rapidly through dry vegetation due to a combination of extreme heat, high winds, and a lack of rain. Additionally, topography plays a role: wildfires burn faster uphill because the flames tend to preheat the fuel above them, increasing the likelihood of rapid ignition, according to the National Interagency Fire Center.
Understanding the variables contributing to wildfire spread is crucial for developing fire prevention and mitigation strategies. Scientists and fire management professionals can better predict wildfire behavior and take appropriate actions to protect lives and property by studying the interactions between wind, fuel, humidity, temperature, and topography.
How do humans contribute to wildfire activity?
According to the U.S. Forest Service, almost 85% of wildfires are caused by humans. Burning debris or garbage, unattended campfires, negligently discarded cigarettes, and arson are common human causes of wildfires.
Where do wildfires occur?
Wildfires are a global phenomenon, particularly prevalent in regions with forested areas, grasslands, and other dry, fire-prone environments. These fires are widespread in countries such as the United States, Canada, Australia, South Africa, and Southern Europe, as well as other regions experiencing frequent drought or high temperatures.
In the U.S., for example, wildfires are most intense in the Western states, including California, Oregon, and Washington, where dry conditions, frequent heatwaves, and winds combine to create highly volatile landscapes. Similarly, Canada’s western provinces, like British Columbia and Alberta, face recurring wildfire seasons. According to the Canadian Interagency Forest Fire Center, vast forested areas and a hot, dry climate contribute to the frequency and severity of these fires.
According to the European Forest Institute, Southern Europe—particularly Spain, Portugal, and Greece—has seen a marked increase in the frequency of summer wildfires in recent decades, driven by hotter, drier conditions. Wildfires also regularly affect South Africa, particularly in the Cape region, where seasonal droughts create conditions conducive to large-scale fires. As these areas remain vulnerable due to their flammable landscapes and climate trends, effective wildfire management strategies are essential to minimize loss of life, property, and biodiversity.
When is wildfire season?
The summer months are most commonly referred to as wildfire season, though this depends on rainfall, wind, and summer temperatures. Historically, wildfire season in the United States has lasted from May through October, but it has lengthened in recent years.
Resources for wildfire preparedness
It’s best to stay informed. Here are a few resources for preparing.
Ready.gov is a site created by the U.S. Department of Homeland Security that provides preparedness checklists, smoke safety tips, and evacuation guidelines. It also includes comprehensive and knowledgeable information on wildfire safety.
The U.S. Department of Agriculture provides detailed information on wildfire statuses and reports across the nation with a real-time map. They also include detailed resources on wildfire causes and information.
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