Background: Fifty years after its initial publication, Rothermel’s model continues to underpin many operational fire modelling tools. Past authors have, however, suggested a possible oversensitivity of the Rothermel model to fuel depth in certain fuel types.

Aims: To evaluate Rothermel model performance based on previous observations of the effect of fuel structure on flame spread through porous fuel beds. This is informed by the consideration of the effect of fuel structure on the physical mechanisms underpinning surface flame spread.

Methods: This study uses an existing dataset of flame spread experiments in pine needle beds to evaluate the effect of fuel structure on Rothermel model predictions of spread rate and reaction intensity.

Key results: Underpredictions of spread rate occurred for compressed fuel beds, apparently driven by an underprediction of the reaction intensity.

Conclusions: A greater understanding of the role of fuel structure on the energy release within the fire front region is therefore required.

Implications: The current tendency for spread rate to be underestimated in the studied fuel beds in quiescent (no wind or slope) conditions requires further consideration given the widespread use of Rothermel’s model in current operational modelling tools.