Australian WRF-Sfire simulations show a fire changes the weather

Fires and the atmosphere are three dimensional and they can interact to produce feedback loops resulting in dramatic and unexpected fire behaviour. What is poorly understood at present is the physical processes that lead to these feedbacks, how and when such feedbacks will occur, and of what magnitude they will be.

We have used WRF-Sfire to run coupled simulations of Australian bushfires where unexpected fire behaviour occurred. The simulations have been run in feedback ‘on' and feedback ‘off' mode in order to assess the impact of a fire on the surrounding atmosphere. The results show significant changes to the mesoscale atmospheric structure as result of energy released by a fire. The simulations show fire plumes interacting with the vertical atmosphere; modification of atmospheric features such as fronts; entrainment of dry air by a fire plume; and fire response to subtle variations in input parameters.

The results provide new insights into the dynamical processes that may occur in a fire environment and provoke challenging questions for the future of both fire simulation models and fire weather services in Australia. In certain weather situations, uncoupled simulations will not provide a complete representation of fire behaviour, which raises questions regarding appropriate development and future use of uncoupled and coupled fire simulators. In addition, the scale of the simulated feedbacks shows that the information required to assess the potential for feedback to occur should be incorporated into fire weather services and operational planning. This is necessary in order to mitigate against the impacts of bushfires and minimise risk during fuel reduction burns.