Knowing how wildfires ignite and what affects their behavior is crucial to control and management of this force of nature. An era of avoidable "megafires" has led to many losses. But if communities are able to change course and create a wildfire-resistant landscape, people can learn to live with fire, not in fear of it.
The first step is understanding how a fire starts and what can be done to stop it. Here's what you need to know about the makeup of fire, its behavior, and its effects on the ecosystems:
The fire ignition triangle.
It all begins with the fire ignition triangle, which describes the elements necessary for starting a fire (all three must be present).
1. Oxygen (air) - to start and sustain combustion. Windy conditions can increase the air supply.
2. Heat - to raise fuel temperatures to their ignition point and to ignite fuels. Common sources of heat are lightning and human activities.
3. Fuel - to sustain and/or carry flames. Combustible materials include trees, shrubs, grasses, and structures.
Wildfires are controlled by removing one side of the fire triangle, which is simple in theory, but not necessarily simple to do. For example, fuels can be treated or removed to create fire breaks; oxygen can be reduced or eliminated by smothering flames with water; and heat transfer can be reduced by covering vegetation with fire retardants.
The fire behavior triangle.
Many factors affect how a wildfire burns, how fast it moves, and how difficult it is to control, which is what creates the fire behavior triangle (not to be confused with the fire ignition triangle). The three sides of the fire behavior triangle are:
1. Weather – includes wind, temperature, cloudiness, moisture, and air pressure. High temperatures and low humidity cause vegetation to dry and wildfires to burn rapidly. Wind not only moves wildfires across landscapes but also supplies oxygen that can cause fires to grow swiftly. Wind also blows embers for miles, igniting new spot fires. Rain and high humidity can slow or extinguish flames, while storms can cause fire activity to increase or become completely unpredictable.
2. Topography – the physical features of an area, including slope and aspect (the direction it faces). Wildfires burn more rapidly when moving up a slope by preheating unburned fuels and making them more combustible. Wind also moves more rapidly up slopes, increasing the speed at which a fire can spread. Draws can act like chimneys and funnel flames upwards. South- and west-facing slopes have drier fuels than north- and east-facing slopes.
3. Fuels – vegetation and structures. Their characteristics have a great effect on wildfire behavior. Large, dense trees burn for hours and generate a lot of heat. Dried grasses, on the other hand, produce a flashy fire that burns quickly and does not generate much heat.
The relationship between fire and the ecosystem.
Though they are a natural part of the ecosystems and prescribed burns are necessary for many reasons, wildfire is still one of the most feared, most fought, and most controversial components of the physical environment.
In recent years, Idaho has experienced several large, long-lasting wildfires, which burned thousands of acres at a time. Much of this destruction can be avoided if people are willing and able to change fire management habits, as scientist Paul Hessburg shares in his TEDx Talk.
Putting the right kind of fire in the right places can reduce the severity of many future wildfires. There are tools you can take to help with this movement, and local organizations are here to show you how.
Idaho Firewise is a non-profit organization that develops and promotes statewide wildfire education for those who live in or visit Idaho. To learn more about wildfire prevention and protection, visit www.idahofirewise.org.