Rothermel Fire Model
Rothermel Surface Fire Spread Model · Also known as: fire spread model, BEHAVE model
The Rothermel fire spread model, developed by Richard Rothermel in 1972, is a mechanistic mathematical model that predicts the rate of fire spread through surface fuels using fuel characteristics, weather, and topography. It forms the theoretical foundation of the BEHAVE fire modeling system used operationally by fire agencies worldwide. The model integrates principles from combustion physics, heat transfer, and fuel science to quantify how fire intensity, fuel moisture, wind, and slope interact to drive wildfire propagation.
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When to use it
Use Rothermel model for pre-fire planning (fuel treatment prioritization, evacuation planning), fire-incident response (tactical resource allocation), and post-fire analysis (forensic fire behavior reconstruction). It is most applicable to surface fires in shrub and grass fuels and in the lightly forested surface layer beneath dense canopies. Less reliable for crown fires (where fuel is elevated above ground) or for extreme conditions outside the model calibration range (very high winds, very dry fuels). Requires careful input data on fuel type and moisture.
Strengths & limitations
- Physically grounded model based on combustion and heat transfer principles, not purely empirical
- Incorporates multiple interacting factors (fuels, weather, topography) in a unified framework
- Well-validated against experimental fires and operational fire behavior observations over 50+ years
- Flexible: can be applied to standard fuel models or custom fuel characterizations
- Operational decision-support tool: predictions inform real-time resource allocation and safety
- Enables scenario analysis: evaluate fire behavior under alternative fuel management or climate conditions
- Rothermel model applies to surface fires; crown fire modeling requires additional extensions (Van Wagner critical crown fire intensity)
- Fuel moisture must be estimated or measured; errors in moisture input propagate to large errors in spread rate prediction
- The 13 standard fuel models are generic; real fuels vary in structure and compaction, and custom calibration is often needed
- Does not account for firespot ignitions or spotting-driven acceleration; assumes contiguous fuel consumption
- Topographic effects are simplified to slope factor; complex terrain (canyons, ridges) may see behavior outside model assumptions
Frequently asked
What are the 13 standard fuel models, and how do I choose one?
The 13 standard fuel models represent common vegetation and fuel assemblages: grass fuels (FM 1–3), shrub fuels (FM 4–6), timber fuels with grass or shrub understory (FM 7–9), timber litter (FM 10), and non-burnable fuels. Choose by visually matching your site's fuel structure to the descriptions in the BEHAVE manual. When in doubt, measure fuel loads and depth to select the closest model.
How sensitive is Rothermel output to fuel moisture?
Fuel moisture has a huge effect on spread rate. Doubling moisture content can reduce spread rate by 50% or more, depending on fuel type. This sensitivity highlights the importance of accurate, current moisture data. Fuel moisture varies with weather: measured morning relative humidity and temperature are used to estimate it. During high fire danger, moisture can change rapidly through the day.
Can Rothermel predict crown fire?
No, Rothermel predicts surface fire spread. Crown fire prediction requires additional models (e.g., Van Wagner critical crown fire intensity, Rothermel crown fire initiation criteria). BehavePlus includes Van Wagner's crown fire extensions, allowing you to assess whether conditions support crown fire ignition and spread.
What should I do if my site does not match any of the 13 standard fuel models?
You can create custom fuel models by specifying fuel loads (by size class), fuel depth, and fuel moisture of extinction for your site. This requires detailed fuel inventory (often plot-based sampling of tree density, shrub biomass, and ground fuel). Alternatively, request input from fire behavior analysts or fuel specialists who can help calibrate a suitable model.
Sources
How to cite this page
ScholarGate. (2026, June 3). Rothermel Surface Fire Spread Model. ScholarGate. https://scholargate.app/en/forestry/rothermel-fire-model
Which method?
Set this method beside its closest kin and read them side by side — the library lays the books on the table; the choice is yours.
- Crown Fire (Van Wagner)Forestry↔ compare
- Fire Weather IndexForestry↔ compare
- Keetch-Byram Drought IndexForestry↔ compare