Simulations of the Waroona fire using the coupled atmosphere–fire model ACCESS-Fire

Abstract

The Waroona fire burned 69 000 ha south of Perth in January 2016. There were two fatalities and 170 homes were lost. Two evening ember storms were reported and pyrocumulonimbus (pyroCb) cloud developed on consecutive days. The extreme fire behaviour did not reconcile with the near- surface conditions customarily used to assess fire danger. A case study of the fire (Peace et al. 2017) presented the hypothesis that the evening ember storms resulted from interactions between the above-surface wind fields, local topography and the fire plume. The coupled fire–atmosphere model ACCESS-Fire has been run in order to explore this hypothesis and other aspects of the fire activity, including the pyroCb development. ACCESS-Fire incorporates the numerical weather prediction model ACCESS (Australian Community Climate and Earth System Simulator, described by Puri et al. 2013) and a fire spread component. In these simulations, the Dry Eucalypt Forest Fire (Vesta) fire spread model is used. In this study we first show that the reconstruction of surface fire spread and simulated fire spread are a good match for the first day; second, we show that the model produces deep moist convection as an indicator of pyrocumulonimbus cloud and, third, we show the fire–atmosphere interactions surrounding the ember showers provided an environment conducive to the observed mass spotting. The simulation results demonstrate that ACCESS-Fire is a tool that may be used to further explore the complex processes and potential impacts surrounding pyroCb development and short-distance ember transport.