Meteorological analysis of an extreme pyroconvective wildfire at Dunalley-Forcett, Australia

Abstract

A major bushfire occurred during January 2013 near the towns Forcett and Dunalley in southeast Tasmania, Australia. Several records were broken by this wildfire, in terms of impacts to eco-systems, infrastructure and lives, and it was the first pyrocumulonimbus documented in Tasmania. The Australian Bureau of Meteorology high-resolution regional reanalysis for Tasmania (BARRA-TA), with 1.5-km spatial resolution, together with in-situ observations, was applied to reconstruct the wildfire event. The antecedent climatic conditions in Tasmania included a large increase in fuel load due to abundant rain one to two years before the event, followed by a heatwave during the summer of 2012/13. In the three periods we identified during the event reconstruction, the second period was the most dramatic, in which a low-level jet was directed downslope in southeast Tasmania to accelerate the fire spread. The BARRA-TA reanalysis revealed the mesoscale features occurring during the fire event additional to the climatic conditions and synoptic patterns documented in past studies. These include a cold front that crossed the fireground during the third period, and thus played a different role compared with some past extreme fire events in terms of airmass lifting and wind direction change. Moreover, mid-level moisture advected into the area was conducive to pyroconvection development.

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