Wildfire Risk Assessments

To understand how a wildfire may affect a property, you must account for the fuels, weather, and topography that control fire behavior. These factors vary across the landscape and over time, which can make risk assessment complex. We clarify it by modeling realistic scenarios important to our clients.

We begin by researching the local fire environment and selecting realistic high-end weather parameters. We then overlay fuels data (type, height, cover, and density) on a digital elevation model that includes elevation, slope, and aspect. Fuels are conditioned pixel by pixel based on weather, shading, aspect, and slope position to determine starting fuel moistures.

For each wind speed and direction, we use a fluid-dynamics model to create a wind vector grid that accounts for canopy cover, topography, and diurnal buoyancy effects. We then simulate tens of thousands of ignitions to estimate flame length, rate of spread, fireline intensity, burn probability, crown fire activity, crown fraction burned, and maximum spotting distance.

These results identify where wildfire risk is highest, what fire behavior to expect, and where fuels treatments are most needed. We also produce fire-spread animations which, along with static maps, clearly show potential fire behavior and risk to individual properties and entire communities.

Examples of Risk Assessment Maps

Major Flow Paths

One of the most useful assessments we model is major fire flow paths—the routes wildfires most often take when thousands of random ignitions are simulated. These paths help identify the most effective locations for fuels treatments.

Burn Probability

We estimate burn probability by simulating 10,000 or more random ignitions across a landscape.

Flame Length

Flame length is a key factor in determining which suppression resources will be effective. Hand crews are generally effective with head-fire flame lengths of 0–4 feet. Dozers, engines, and aircraft can be effective between 4 and 8 feet. Control efforts at the head are usually ineffective when flame lengths reach 8 feet or more.

Rate of Spread

Rate of spread helps determine how much time is available to evacuate a community or to dispatch and engage suppression resources.

Fireline Intensity

Fireline intensity is related to flame length and rate of spread. It is especially useful for predicting a fire’s effects on vegetation and human values. Lower-intensity fire causes less plant mortality and less damage to structures and other values than higher-intensity fire.

Crown Fire Activity

Areas predicted to support passive crown fire (torching) or active crown fire (running crown fire) become elevated ember sources. These embers can travel over firelines and create spot fires ahead of the main front. Reducing passive and active crown fire upwind of values is an effective strategy for protecting homes and communities.