The Rothermel surface fire spread model and associated developments: A comprehensive explanation

The Rothermel surface fire spread model, with some adjustments by Frank A. Albini in 1976, has been used in fire and fuels management systems since 1972. It is generally used with other models including fireline intensity and flame length. Fuel models are often used to define fuel input parameters. Dynamic fuel models use equations for live fuel curing. Models have been developed for the effect of cross-slope wind and for fire spread in directions other than head fire. Equations for the Rothermel model and associated models are presented for easy reference. The influence of input variables on results is examined. While the spread model is used in the U.S. National Fire Danger Rating System (NFDRS), there are significant differences. The NFDRS equations and fuel models are given. This paper is intended to serve as a reference for those interested in the foundation of wildland fire modeling. System developers will benefit from equations from various sources being in one document. Developers of custom fuel models will find information on the impact of fuel parameters on rate of spread calculations.