Understanding the drivers of pyroCb development over southeast Australia

The incidence and magnitude of extreme wildfires have increased markedly in Australia. In some extreme wildfires, violent pyroconvection can manifest as pyrocumulonimbus clouds (pyroCb), which impact not only the surface but also the atmosphere, leading to dangerous escalation of wildfire risk and severe stratospheric pollution. Climate change could amplify the conditions associated with pyroCb development, so a better understanding of pyroCb drivers and their impact mechanisms is crucial for the prediction and management of pyroCb development. Previous studies have shown that atmospheric instability, surface fire weather conditions, vegetation type, and topography are important conditions affecting pyroCb development, but the synergy and extent of the contribution of these factors have not been systematically analyzed. Also, previous studies have focused more on individual events or a certain region, lacking analysis of the drivers and occurrence patterns of pyroCb over larger spatial and temporal scales. This study therefore examined atmospheric, surface weather, topographic and vegetation conditions associated with pyroCbs and standard wildfires occurring over southeast Australia, including the mainland of New South Wales (NSW), Australian Capital Territory (ACT) and Victoria (Vic) from 1980-2020. Then we used logistic models to analyze the relative importance and regional differences of pyroCb drivers. We found that for the whole southeast Australia, atmospheric variables are the most important pyroCb drivers, followed by topographic and surface weather variables. Fuel moisture content was found to be the most important among the given surface weather variables. However, the importance of pyroCb drivers varied from region to region. In NSW (including ACT), atmospheric and surface weather variables were more important than topographic variables, while in Vic, topographic variables were the most important, followed by atmospheric and vegetation variables, with surface weather variables having less influence on pyroCb incidence. The results provide insights that can be drawn upon to better predict the likelihood of pyroCb occurrence and the risk of extreme wildfires over southeastern Australia.