Examination of wind speed thresholds for vorticity-driven lateral fire spread

Recent research has demonstrated that under conditions of extreme fire weather, bushfires burning in rugged terrain can exhibit highly atypical patterns of propagation, which can have a dramatic effect on subsequent fire development. In particular, wildfires have been observed to spread laterally across steep, lee-facing slopes in a process that has been termed ‘fire channelling'. Fire channelling, in turn, has been associated with serious escalation in fire activity and the development of pyro-cumulonimbus storms. Coupled fire-atmosphere modelling using large eddy simulation has indicated that the fire channelling phenomenon occurs in response to fire-induced vorticity on the fire's flanks in the immediate lee of a ridge line. In this presentation we provide an overview of previous investigations in the fire channelling phenomenon, using the WRF-SFire model, and highlight recent modelling that specifically considers the effect of wind speed in generating the fire-induced vorticity necessary to drive the lateral spread associated with fire channelling. The modelling results are discussed with reference to laboratory-scale experimental fires examining the same effect.