Field-based generic empirical flame length–fireline intensity relationships for wildland surface fires

Abstract

Background Fireline intensity (If) quantifies the power of the fireline and is used for various purposes. If and flame length (Lf) are relatable to each other using an empirical power function, which has been considered fuel-specific. Aims The aim of this study was to develop generic Lf − If relationships based on a robust set of field head fires from the literature (n = 797) conducted worldwide in forest, shrubland and grassland. Methods Lf was determined from the base of the fuel bed for comparability across fires in different fuel heights, and the effect of vegetation type was examined. Key results Although If could be approximately described using the same function in forest and shrubland, fires in grassland required different fitted coefficients; we speculate that fuel particles’ surface area-to-mass ratio is the main fuel metric influencing flame structure. Conclusions Fuel-generic relationships for If are reasonably accurate and encompass the high end of surface fire If. Previous studies suggested their unviability, most likely because of limitations in the number of observations and data ranges, difficulty in objectively measuring Lf and variation in Lf definition. Implications The generic relationships presented in this work will be of interest for research and management purposes when specific models for If are non-existent.