Wildfire Temperatures: How Hot Can Wildfires Burn?

Discover how hot wildfires can burn, the factors influencing their temperatures, and the science behind wildfire heat with expert guidance from the WFCA.

Knowing how hot a fire can burn is crucial for effective management and safety. Understanding the temperature range helps in predicting fire behavior, assessing potential damage, and implementing appropriate firefighting strategies. It also aids in planning for safety measures, protecting property, and mitigating risks to people and wildlife.

Temperature Examples

Different flames burn at different temperatures because of their fuel, how efficiently they burn, and how much oxygen they get. For example, a candle flame, which burns paraffin wax, usually heats up to about 800°F to 1,200°F because it has limited oxygen and burns steadily.¹ A match flame, which has a quick chemical reaction, gets really hot for a short time but then cools down fast. On the other hand, a bonfire burns wood and gets a lot of oxygen, so it can reach temperatures between 1112°F and 1832°F or even higher because it has more fuel and burns more intensely.²

Temperature Ranges in Wildfires

During a wildfire, all three types of fires—ground fires, surface fires, and crown fires—can occur simultaneously. The amount of each type can vary greatly from day to day or even minute to minute, depending on factors like fuel, topography, and weather conditions. Changes in any of these factors can cause a ground fire to become a surface fire or a surface fire to escalate into a crown fire, and vice versa.

Surface Fires: Surface fires burn through materials like needles, moss, lichen, and small vegetation near the ground. These fires primarily spread by flaming combustion and largely determine the fire’s expansion. They can increase in intensity based on the amount of surface fuel, its moisture content, and environmental factors such as slope and wind speed. If conditions are right, surface fires can intensify enough to scorch or even consume the forest canopy, potentially transitioning into crown fires.

Crown Fires: Crown fires burn through the forest canopy, consuming live and dead foliage, branches, and tall shrubs. They usually start from surface fires and can be passive or active. Passive crown fires burn individual trees or small groups, while active crown fires spread rapidly through the canopy, creating a continuous wall of flames from one tree crown to the next.

Ground Fires: Ground fires occur primarily in decayed roots below the surface and in the duff layer, which consists of compacted dead plant material like leaves, bark, and twigs. These fires are sustained by glowing combustion without visible flames and often go unnoticed for extended periods due to their minimal smoke output. Because they spread slowly, ground fires can persist underground, making them challenging to detect and manage.³

Factors Influencing Wildfire Temperatures

Wildfire temperatures and behavior are influenced by several key factors, including weather, topography, and fuel type. Each of these elements plays a crucial role in determining how a wildfire spreads and intensifies. Understanding these factors helps in predicting fire behavior and managing wildfire risks more effectively.

Type of Fuel: A large amount of flammable material, or high fuel load, results in a more intense fire that spreads quickly. Dry fuel burns faster and is harder to control. Smaller, dry fuels like grass ignite quickly, while larger fuels like logs take longer. As the fire progresses, it dries out nearby fuel, making it easier to ignite. Well-spaced fuels dry out faster and burn more rapidly than tightly packed fuels, which retain moisture and absorb more heat.

Weather Conditions: Weather also plays a role in wildfires, affecting their temperatures and spread through three main factors: temperature, wind, and moisture. Higher temperatures dry out fuels like wood and underbrush, making them more likely to ignite and burn faster. Wind accelerates fire spread by providing extra oxygen and pushing flames across the land, and it can even generate its own wind patterns, including fire whirls that spread flames further. Conversely, high moisture levels, from humidity or precipitation, can slow down or reduce the intensity of wildfires by making fuels harder to ignite. Low humidity increases the likelihood of wildfires starting, while rain helps suppress them by raising fuel moisture levels.

Topography: Topography greatly affects wildfire behavior, especially the slope of the land. Fires spread faster uphill because they preheat the fuel above, with steeper slopes accelerating this process. Fires typically move in the direction of the wind, which usually blows uphill, enhancing this effect. However, once a fire reaches the top, it struggles to advance downhill due to less effective preheating. Additionally, steep slopes can lead to problems like erosion and debris flows after the fire has burned through vegetation. Despite their destructiveness, wildfires can reduce underbrush and encourage new plant growth.⁴

The Science Behind Wildfire Heat

Combustion Process: Combustion is a chemical reaction where oxygen reacts with fuel, producing heat and light in the form of a flame. This reaction happens quickly, generating more energy than can escape, which raises the temperature of the reactants and speeds up the process. For combustion to start, the fuel must reach a specific ignition temperature. The rate of combustion can vary depending on the amount of oxygen available; when it’s fast enough to create a flame, it’s known as burning. Fire continues as long as there is fuel, oxygen, and heat, which are the three components of the fire triangle.⁵

Heat Transfer Mechanisms: Heat transfer describes how thermal energy moves to balance out temperatures. The three main methods are conduction, where heat moves through direct contact; convection, where heat travels through fluids like air or water by circulation; and radiation, where heat transfers through waves, like sunlight. Another method, evapotranspiration, moves heat when water evaporates from surfaces like plants and soil.⁶