The distribution of fuels is recognised as a key driver of wildland fire behaviour. However, our understanding of how fuel density heterogeneity affects fire behaviour is limited because of the challenges associated with experiments that isolate fuel heterogeneity from other factors. Advances in fire behaviour modelling and computational resources provide a means to explore fire behaviour responses to fuel heterogeneity. Using an ensemble approach to simulate fire behaviour in a coupled fire–atmosphere model, we systematically tested how fuel density fidelity and heterogeneity shape effective wind characteristics that ultimately affect fire behaviour. Results showed that with increased fuel density fidelity and heterogeneity, fire spread and area burned decreased owing to a combination of fuel discontinuities and increased fine-scale turbulent wind structures that blocked forward fire spread. However, at large characteristic length scales of spatial fuel density, the fire spread and area burned increased because local fuel discontinuity decreased, and wind entrainment into the forest canopy maintained near-surface wind speeds that drove forward fire spread. These results demonstrate the importance of incorporating high-resolution fuel fidelity and heterogeneity information to capture effective wind conditions that improve fire behaviour forecasts.

The wildfire model FIRETEC simulates the large coherent eddies of the wind-flows induced by the canopy. It has been qualitatively validated in its ability to simulate fire behavior, but there is still a need to validate physical submodels separately. In the present study, the dynamics and turbulence of the flow simulated by FIRETEC are validated in a manner similar to other air-flow models without fire, through comparison with measurements associated with flows within continuous and discontinuous forests captured through in situ and wind-tunnel experiments with neutral thermal stratification. The model is shown to be able to reproduce accurately all essential features of turbulent flow over both forests. Moreover, a short sensitivity study shows that the model is not very sensitive to uncertain parameters such as vegetation drag coefficient. Finally, it is shown in the discontinuous forest case that wind gusts on fuel-breaks can be very strong and significantly higher than in surrounding canopies, even if their directions are more stable. These results and others briefly reviewed in the present paper allow better understanding of wind-flow perturbations induced by fuel-breaks. This new validation added to previous ones confirms the ability of FIRETEC for investigating effects of fuel-break design on fire propagation.