Observations of Wildfire–Atmosphere Interactions over Mountainous Terrain, Southeast Queensland, Australia

Abstract Mountains create their own weather through topographic modification of the prevailing synoptic meteorology. As a result, wildfires in mountainous terrain may exhibit erratic and extreme behavior as ridges and valleys modify the prevailing winds. Here, we present a case study analysis of a wildfire that occurred in mountainous terrain in subtropical eastern Australia. The wildfire was observed to transition between a wind-driven and plume-driven wildfire on at least three occasions with a periodicity of around 60 min prior to the arrival of a shortwave trough. The Weather Research and Forecasting (WRF) Model was used to investigate the surface wind field and vertical thermodynamic properties of the atmosphere. Results aligned with observational data indicating that topographic lifting caused by only moderate changes in terrain may have contributed to the coupling of the wildfire plume to an elevated layer of humidity leading to rapid pyrocumulus (pyroCu) development. Strong wind shear caused the pyroCu to detach from the wildfire on at least three occasions with a subsequent return to a wind-driven wildfire. Mobile weather radar identified pyrometeors in the pyroconvective plume, which ignited new spot fires causing a rapid fourfold increase in the size of the wildfire. Our results highlight the importance of understanding the influence of what may be perceived as only subtle to moderate changes in terrain on local meteorological conditions and wildfire behavior, and the potential benefits of access to real-time high-resolution weather radar data for monitoring wildfire–atmosphere interactions including ember transport. Significance Statement The purpose of this study is to understand the complex interactions that occur between mountains, the atmosphere, and wildfires to enable more accurate prediction of wildfire behavior. We show that even moderate size changes in topographic elevation of a few hundred meters height may cause the smoke plume from a wildfire to connect with layers of higher humidity in the atmosphere contributing to a rapid increase in the size of the wildfire. This results in a change in the behavior of the wildfire causing it to rapidly become larger and more extreme with its convective plume capable of transporting embers many kilometers downwind that may start new wildfires. We show that mobile weather radar can provide time-critical information on these processes and recommend further research into their operational deployment to wildfires to support wildfire management.