On the meteorological and hydrological mechanisms resulting in the 2003 post-fire flood event in Alpine Shire, Victori

Abstract

This paper describes an analysis of the factors surrounding a post-fire flooding event that occurred in the Alpine Shire, Victoria, Australia in late February 2003. Flash flooding occurred because of highly localised thunderstorms and was enhanced by the burned landscape. In addition, our analysis of the resulting situation suggests that other contributing factors included the storm cells likely being pulse wet microburst, cell regeneration over the same area, and the steepness of the Buckland River Catchment. The synoptic conditions surrounding the event suggest that the major drivers of the extreme rainfall event were the high levels of precipitable water in the atmosphere and enhanced atmospheric instability (including associated high CAPE values) from increased surface heating due to the reduction in surface albedo and soil moisture of the recently burned fire surface. In addition, weak upper atmospheric winds during the flash flood event contributed to slow storm movement. Hydrological modelling of the flash flooding event further indicated that fire-induced soil hydrophobicity was likely to have caused an enhancement of the hydrological response of the catchment. With an increase in frequency of fires expected in the Alpine Shire associated with anthropogenic climate change, the relationship between fire and flood, even for rare events, has implications for emergency managers and Alpine Shire residents. It is intended that the results of this study will assist in emergency preparedness and thereby contribute to a reduction in the vulnerability of fire-affected communities to post-fire flash floods.