Disaster Preparedness Tips: Wildland Fire Behavior Explained

West Coast Wildfire

While it's not always possible to predict the precise trigger or spark for a wildfire, its risk can be estimated to some extent when one understands the patterns it follows. The term “wildland fire behavior” describes how fuel ignites, flame develops, and fire spreads, as well as common factors that influence it.

With this information, you can be alert, prepare for a natural disaster before it strikes, and understand what to do when it’s happening. Read ahead to find out everything you need to know!

Wildland Fire Causes

Wildland Fire

Wildland fires can occur due to natural reasons or be human-caused. Unfortunately, the latter type is much more common, accounting for 85%-90% of the total number.

Some of the main causes of wildfires include:

  • Unattended campfires
  • Fallen power lines
  • Extensive periods of drought
  • Discarded cigarettes
  • Lightning
  • Vehicle crashes and engine sparks
  • Arson
  • Equipment malfunctions

The Fire Behavior Triangle

Wildfire in the Forest

When it comes to wildfire rate of spread, it often depends on a combination of three main factors: fuels, weather, and topography. Together, these three elements make up what is known as the “fire triangle”. Let’s take a closer look at each of these components.

1. Fuels

Any material that can burn is fuel for a fire. During a wildland fire, fuel often consists of:

  • Grasses
  • Shrubs
  • Trees
  • Dead leaves
  • Fallen pine needles 

Typically, the more of these materials are available, the bigger the wildland fire can turn out. However, it’s not only the fuel’s quantity that matters - its composition, moisture level, chemical makeup, and density also determine its degree of flammability. 

The most critical factor when it comes to fuel quality is moisture. For instance, live trees usually contain a lot of moisture, while dead logs have very little - it’s needless to say that the latter will catch fire and burn way faster. This factor mostly depends on the humidity level in the area and the amount of precipitation throughout the season.

2. Weather

Weather conditions such as temperature, humidity, and wind also play a crucial role when it comes to wildfire behavior:

 

  • Wind supplies oxygen to the fire and pushes it toward new fuel sources.
  • The ambient temperature determines the fuel temperature, as fuels attain their heat by absorbing solar radiation from around them. Hence, the higher the ambient and fuel temperatures are, the more chances there are for a wildland fire to occur.
  • The level of humidity signifies the amount of water vapor in the air. High humidity moistens the fuel and makes it less susceptible to ignition.

Thus, even though wildfires can take place at any moment if the conditions are right, the time of the year and geographic region have a huge influence on the likelihood of such emergencies. For instance, the wildfire season in the western US is June-October, while the southeastern part of the country should be more alert from March to May.

3. Topography

Topography describes the characteristics of the land surface, such as canyons, valleys, rivers, and so on. Such features can influence the spread of wildfire in different ways.

For instance, a rocky slope would be an excellent natural fire break because of the lack of fuel and plenty of open space.

It’s also important to take elevation, slope, and aspect into account. Higher elevations tend to be drier but colder than the lower ones, while north-facing slopes dry out slower than the rest. Besides, it’s essential to remember that the fire climbs faster than it travels downhill. The steeper the slope, the easier it will be for the flames to spread, as they can preheat the upcoming fuels with rising hot air.

Types of Wildland Fires

Wildland Fire at Night

There are three different types of wildfires:

  • Ground fires (underground or subsurface fires) happen in areas with deep accumulations of humus, peat, or similar dry vegetation. Such fires spread slowly yet are challenging to put out. Sometimes, especially during extended periods of drought, such fires can smolder all winter underground and then reappear on the surface in spring.
  • Surface fires typically burn only surface litter and duff. Such fires are easy to suppress and put out and cause the least damage to the environment.
  • Crown fires happen in forests and burn trees up their entire length, reaching the top. Such wildfires are extremely dangerous and intense.

How Are Wildfires Suppressed?

Forest Fire

Firefighters can control and put out a fire by removing one of the three essential ingredients it needs to burn. Since it’s virtually impossible to cut the access of oxygen to a wildfire, there are two remaining options:

  • Heat is removed through the application of water or fire retardant with pumps, wildland fire engines, or with the help of helicopters and airplanes.
  • Fuel is being taken away by digging and cutting flammable vegetation either with manual tools or by implementing heavy equipment like bulldozers. Another technique is to set fires deliberately to rob an approaching wildfire of fuel.
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    Note that it’s impossible to fight a wildfire for people without special training. However, knowing the key principles of wildland fire behavior and the main causes of these emergencies is a great foundation for disaster preparedness. Keep this information in mind and take all the necessary precautions, especially if you live in high-risk areas.