Background

Fireline intensity (I_f) quantifies the power of the fireline and is used for various purposes. I_f and flame length (L_f) 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 L_f − I_f relationships based on a robust set of field head fires from the literature (n = 797) conducted worldwide in forest, shrubland and grassland.

Methods

L_f 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 I_f 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 I_f are reasonably accurate and encompass the high end of surface fire I_f. Previous studies suggested their unviability, most likely because of limitations in the number of observations and data ranges, difficulty in objectively measuring L_f and variation in L_f definition.

Implications

The generic relationships presented in this work will be of interest for research and management purposes when specific models for I_f are non-existent.

Keywords: combustion metrics, fire behaviour, fire management, forest, fuel metrics, grassland, head fires, shrubland, surface area-to-mass ratio.