Why Australia's Bushfires Are Not More Of The Same In A Place Known For Drought & Heat
Every time a weather extreme occurs, some people quickly jump in to say we’ve been through it all before: that worse events have happened in the past, or it’s just part of natural climate variability. The recent bushfire crisis is a case in point. Writing in The Australian recently, columnist Gerard Henderson said: In Victoria, there were further huge fires in 1983 and 2009. But until now, there was no suggestion that the state’s future would be one of continuing apocalypse.
Of course, Australia has a long history of bushfires. But several factors make eastern Australia’s recent crisis different to infamous bushfires in the past. First is the enormous geographic spread of this season’s fires, and second, the absence of El Niño conditions typically associated with previous severe fires. Thirdly and most important, these fires were preceded by the hottest and driest conditions in Australian history.
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Right now, ENSO is not active, and a very strong positive IOD event – the strongest since 1997 – has just ended. Positive IOD events typically result in below average winter-spring rainfall over southern and central Australia, and are often associated with more severe bushfire conditions. There has also been a marked warming of the atmosphere over Antarctica, known as sudden stratospheric warming. This has led to a weakening of the polar vortex, resulting in more negative conditions in the Southern Annular Mode – essentially the north-south movement of the westerly wind belt that loops around Antarctica.
New Australian research has found weakening and warming of the stratospheric polar vortex over Antarctica significantly increases the chances of hot and dry extremes, including more severe fire weather conditions across subtropical eastern Australia than is normal for spring-early summer. This combination of unusual natural variability in the Indian and Southern Oceans, the unprecedented lack of winter rains in 2017, 2018 and 2019, and Australia’s hottest summer on record, have contributed to the extreme drought currently affecting 100% of New South Wales and 67.4% of Queensland.
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https://theconversation.com/some-say-weve-seen-bushfires-worse-than-this-before-but-theyre-ignoring-a-few-key-facts-129391