Abstract
The 2019/20 Black Summer bushfire disaster in southeast Australia was unprecedented: the extensive area of forest burnt, the radiative power of the fires, and the extraordinary number of fires that developed into extreme pyroconvective events were all unmatched in the historical record. Australia’s hottest and driest year on record, 2019, was characterised by exceptionally dry fuel loads that primed the landscape to burn when exposed to dangerous fire weather and ignition. The combination of climate variability and long-term climate trends generated the climate extremes experienced in 2019, and the compounding effects of two or more modes of climate variability in their fire-promoting phases (as occurred in 2019) has historically increased the chances of large forest fires occurring in southeast Australia. Palaeoclimate evidence also demonstrates that fire-promoting phases of tropical Pacific and Indian ocean variability are now unusually frequent compared with natural variability in pre-industrial times. Indicators of forest fire danger in southeast Australia have already emerged outside of the range of historical experience, suggesting that projections made more than a decade ago that increases in climate-driven fire risk would be detectable by 2020, have indeed eventuated. The multiple climate change contributors to fire risk in southeast Australia, as well as the observed non-linear escalation of fire extent and intensity, raise the likelihood that fire events may continue to rapidly intensify in the future. Improving local and national adaptation measures while also pursuing ambitious global climate change mitigation efforts would provide the best strategy for limiting further increases in fire risk in southeast Australia.
Highlights
The 2019/20 Black Summer bushfire disaster in southeast Australia was unprecedented: the extensive area of forest burnt, the radiative power of the fires, and the extraordinary number of fires that developed into extreme pyroconvective events were all unmatched in the historical record
Some assessments had projected that the influence of human-caused climate change on increasing fire weather days in southeast Australia should be directly observable by 202018, while other studies suggest that indicators of increasing fire risk in this region will only become detectable outside of the range of natural variability much later this century[19]
We examine the ways that climate variability and climate change are altering the risk of large and extreme forest fires in southeast Australia, while acknowledging that the ultimate impact of fires on people and ecosystems is determined by a range of non-climatic factors that fall outside of the scope of this review
Summary
From the 2019/20 fires in southeast Australia was the highest on record for every month of the spring and summer fire season (Fig. 1b and Supplementary Fig. 1). The evolution of landscape conditions that increase forest fire risk in southeast Australia (Box Fig. 1) involves a range of climate processes These climate factors affect the four switches[56] that are all necessary for large forest fires to develop: Fuel load (biomass): Australia’s temperate forests are primarily composed of eucalypts, and are among the most fire-prone forest type in the world[1]. These environments generally have high fuel loads, comprising leaf and bark litter, dead wood and living foliage. Frontal weather systems are associated with increased atmospheric instability, which can enhance the vertical development of bushfire plumes, making fires more likely to couple with the atmosphere and develop into extreme pyroconvective fire events
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