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.
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.
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.
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.
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.
The generic relationships presented in this work will be of interest for research and management purposes when specific models for If are non-existent.
Keywords: combustion metrics, fire behaviour, fire management, forest, fuel metrics, grassland, head fires, shrubland, surface area-to-mass ratio.