How do Wildfires Start and Spread?

Wildfires can start and spread quickly, as fast as 14mph. Learn more about how and why this happens with guidance from the Western Fire Chiefs Association (WFCA).

Wildfires, no matter how they are ignited, can spread quickly across large areas of land. They can spread at speeds up to 14 miles per hour¹, depending on vegetation and other flammable materials that provide fuel for a fire. Weather conditions impact the fire’s spread, and topography affects how a fire advances. Fires tend to advance more quickly uphill than downhill. Home hardening and creating a defensible space around a home can help minimize the spread of wildfires.

What is needed for a wildfire to start?

Wildfires are a type of uncontrolled fire that can spread quickly across land. They are commonly caused by human activity but can also be started by natural events such as lightning strikes. For any fire to occur, three things are required: heat, fuel, and oxygen.

Heat is the initial source of ignition for a wildfire. It can come from a variety of sources, including lightning, volcanoes, and many human activities. Once a spark or flame is created, it can ignite nearby vegetation and start a wildfire.

Fuel refers to the vegetation, trees, shrubs, and other materials that are available to burn. In order for a wildfire to spread, there needs to be enough fuel to keep the fire going. This is why wildfires often occur in areas with plentiful, dry vegetation, such as forests, grasslands, and chaparral.

Oxygen is present in the air and is necessary to sustain a fire. As wildfire burns, it consumes oxygen and releases carbon dioxide and other gases into the atmosphere. The more oxygen there is, the more intense the fire will be.

When these three elements come together, a wildfire can start and grow quickly, especially during periods of hot and dry weather. This is why wildfires are more common in areas with arid climates, and why they tend to occur more frequently during the summer months. To prevent wildfires, it is important to be cautious and follow local regulations regarding campfires, fireworks, and other activities that may create a spark.

What are the Most Common Causes of Wildfires?

Nearly 85% of wildland fires in the United States are caused by humans.² The most common human activities that cause a wildfire include:

1. Campfires: Campfires that are not properly extinguished can quickly spread and start wildfires. Be sure to follow the proper safety precautions when enjoying a campfire.
2. Cigarettes: Cigarettes that are not fully extinguished or are thrown out of car windows can start wildfires. Always dispose of cigarettes in a fire-safe receptible, and never dispose of them on the ground.
3. Arson: Intentionally setting fires with the purpose of destruction is a serious and punishable crime.
4. Powerlines: Powerlines that are damaged or malfunctioning can create sparks that start wildfires.
5. Equipment: Equipment such as lawnmowers, chainsaws, and other machinery can create sparks that start wildfires. Always exercise caution when using tools that may generate a spark, and keep equipment out of areas where there is fuel available, and conditions are especially dry or windy.

Natural causes of wildfires include:

1. Lightning: Lightning strikes can start wildfires, especially in dry and windy conditions.
2. Volcanic eruptions: Volcanic eruptions can create hot ash and debris that can start wildfires.
3. Spontaneous combustion: Decomposing organic material such as peat moss can spontaneously ignite and start wildfires.

How is Climate Change Affecting Wildfires?

Climate change significantly impacts the frequency and severity of wildfires around the world. Rising temperatures, changing precipitation patterns, and more frequent and severe droughts all contribute to an increased risk of wildfires. Here are some of the ways that climate change affects wildfires³:

• Longer wildfire seasons: Warmer temperatures cause snow to melt earlier in the year, which means that wildfire season starts earlier and lasts longer.
• Drier conditions: Rising temperatures and changing precipitation patterns have made many areas drier, creating ideal conditions for fires to start and spread.
• More intense fires: Drier conditions and warmer temperatures cause fires to burn hotter and more intensely, making them more difficult to control.
• More frequent fires: The combination of longer wildfire seasons, drier conditions, and more intense fires leads to an increase in the number of wildfires.
• Increased risk of lightning: Climate change increases the risk of lightning strikes, which are a major cause of wildfires.

Climate change exacerbates the conditions that lead to wildfires, making them more frequent, more severe, and more difficult to control.

How do Wildfires Spread?

Wildfires mainly spread through vegetation, such as trees, bushes, and grasses. They can also spread on the wind, as burning embers are carried over longer distances and can ignite new fires in different locations. The speed at which wildfires spread depends on several factors, including wind speed, terrain, and fuel availability.

Wildfires grow quickly in certain conditions, sometimes reaching speeds of up to 14 miles per hour¹ (22.5 kilometers per hour) in extreme cases. The speed at which a wildfire spreads is measured in terms of its rate of spread, which is typically expressed in feet or meters per minute. The rate of spread can vary widely depending on the specific conditions of the fire, but it is faster in areas with high winds, steep terrain, and dry vegetation.

What Can be Done to Minimize the Spread of Wildfire?

There are several things that can be done to minimize the spread of wildfires⁴. Here are some of the most effective strategies:

1. Clear vegetation around homes and other structures: Creating a defensible space around homes and other structures can help prevent the spread of wildfires.
2. Follow local burn bans and fire restrictions: Many areas have restrictions on open fires and other activities that can increase the risk of wildfires. It is important to follow these restrictions and to avoid activities that could spark a fire.
3. Report wildfires immediately: If you see a wildfire, report it to the local authorities immediately. Early detection and response can help prevent a fire from spreading.
4. Be prepared to evacuate: If a wildfire is approaching your area, be prepared to evacuate quickly. Have a plan in place and make sure you have essential items, such as medications, important documents, and clothing, ready to go.
5. Practice fire-safe behavior: When spending time in areas with a high risk of wildfires, practice fire-safe behavior. This includes properly extinguishing campfires, not smoking in areas with dry vegetation, and avoiding the use of fireworks.

Preventing uncontrolled fires from starting in the first place, through safe practices and proper land management, is the best strategy for minimizing potential damage. However, if a wildfire does occur, early detection and response, along with proper preparation and fire-safe behavior, can help prevent it from spreading.