What Causes Wildfires? Human Activity and Weather Conditions
It can feel like wildfires are becoming an ever-present problem in today’s world. Whether you live in a wildfire-prone area, notice the smell of smoke as a regular part of summer afternoons, or are constantly seeing news of new fires breaking out, it’s easy to understand why they feel so prevalent. But because wildfires occur so frequently, you may find yourself wondering: what exactly counts as a wildfire, and what causes them?
Defining Wildfires
According to the U.S. Department of Agriculture, "wildfires are unplanned fires that occur in wildlands such as forest, rangelands or grasslands" (USDA | Wildfire). In the United States, wildfires are especially common in the western states, with the highest risk occurring during the summer and fall months.
Because wildlands vary widely, wildfires can also take different forms. A fire burning in a dense forest behaves differently from one burning through open brushland or grassland. But what causes these differences?
The primary distinction lies in the type of fuel available. According to the National Park Service, a brush fire burns primarily shrubs, brush, and scrub growth, while a forest fire mainly consumes trees. The type and amount of fuel present directly influence how quickly a fire spreads and how intensely it burns.
Prescribed Burns vs. Wildfires
Unlike wildfires, which are unplanned and often dangerous, fire officials sometimes intentionally set planned fires in wildland areas. Known as prescribed burns, controlled burns, or prescribed fires, these practices are used to help maintain forest health (National Geopgraphic).
Controlled burns are carefully planned and conducted only when conditions are safe for both the public and firefighting personnel. Their primary purpose is to remove excess fuel that could otherwise intensify a wildfire. This fuel often includes dead grass, fallen branches, dead trees, and dense undergrowth (National Geopgraphic).
The logic behind prescribed burns relates directly to the “fire triangle,” a concept used by firefighters to explain that fuel, oxygen, and heat must all be present for a fire to occur. By reducing available fuel, prescribed burns help prevent future wildfires or limit their severity.
What Causes Wildfires?
Humans are the leading cause of wildfires. The National Park Service reports that nearly 85% of all wildfires in the United States are caused by human activities. The most common causes include:
- Unattended campfires
- The burning of debris
- Equipment use and malfunction
- Negligently discarded cigarettes
- Intentional arson
In addition to human causes, some wildfires start naturally. Lightning is by far the most common natural cause, though volcanic activity can also ignite fires in rare cases.
It is important to note that while these causes may spark a fire, the right conditions must also be present. As explained by the fire triangle, fuel, oxygen, and heat are all required for a fire to ignite. Human and natural ignition sources typically provide the heat component, while environmental conditions determine whether a fire can spread.
What Can You do to Prevent Wildfires?
Because most wildfires are caused by human activity, individuals can play an important role in preventing them.
Before starting a campfire or engaging in activities involving fire, check conditions carefully. If the weather is dry or windy, consider postponing fire use altogether. When building a campfire, choose an open area away from flammable materials.
Always extinguish campfires completely. A common method includes:
- Dousing the fire with water
- Stirring the embers
- Dousing the fire again
- Stirring until everything is cold
In addition, keep vehicles off dry grass, as hot exhaust systems can ignite vegetation. Properly maintaining equipment and vehicles can also reduce the risk of accidental sparks.
Wildfires are a natural part of many ecosystems, but their increasing frequency and severity have made them a growing concern. Understanding what wildfires are, how they differ based on the fuel they burn, and what causes them helps clarify why they can be so dangerous. While some fires start naturally, most are the result of human activity, making prevention especially important. Practices like prescribed burns reduce excess fuel and help limit wildfire intensity, and individuals can further reduce risk by using fire responsibly. Through awareness, preparation, and prevention, the impacts of wildfires can be reduced.