Observations of wildfire spread dynamics in southern Australian grasslands

Background Wildfire propagation is inherently non-steady, although forecasts of their spread focus on a pseudo-steady state assumption. Aims To investigate the variability in rate of fire spread of wildfires in southern Australian grassland landscapes, and the effect of landscape features in inhibiting fire propagation. To evaluate the adequacy of grassfire rate of spread models currently used in Australia. Methods We reconstructed the propagation of six wildfires in grassland fuels and characterised the unsteady nature of rate of spread. We also analysed the effect of barriers to fire spread in slowing or halting wildfire propagation. Key results Headfire rate of spread in wildfires was observed to be non-steady, with peaks in forward rate of spread being on average 2.6-times higher than mean values. The rate of spread had an average coefficient of variation of 88%. Areas of fuel discontinuity, such as roads, did not stop fires under moderate burning conditions, but resulted in slowing the average rate of fire spread. Conclusions Analysis of wildfire observations is key to understand fire behaviour features that are not replicable in experimental or modelling environments. Findings from the analysis can support fire-fighting safety awareness and inform landscape fire propagation modelling.