A big bushfire skirting the suburbs of Sydney, Australia, has been made more likely because of the preceding hot and drying start to autumn. The fire season has been extended by several weeks as summer heat kept recurring.
This sort of heatwave, during spring or autumn, shows a greater divergence from the long-term average than a summer or winter heatwave.
“I would bet my house on it, that there’s a climate change signal in this most recent heatwave,” said Sarah Perkins-Kirkpatrick, climate scientist at University of New South Wales.
Perkins-Kirkpatrick has not hedged her bets on what she believes is influencing March and April’s record-breaking heatwave, and said that the occurrence of this type of weather event was increasing.
Senior climatologist Blair Trewin, from the Bureau of Meteorology, said the conditions have been more like mid-summer than mid-autumn.
Australia recorded temperatures of 45 Celsius in late March for the first time in history. Sydney and Adelaide had their hottest or equal-hottest April days on record.
Indeed, the states of South Australia, Victoria and New South Wales all broke many records. In Victoria, the state temperature record was exceeded by one and a half degrees, in almost a third of measuring locations.
“When you’re breaking a record over a whole state by that sort of margin, that’s a significant event,” Trewin said.
“In the past five years, we’ve seen two particularly significant heatwaves in September, in 2013 and 2017 and a major one in October 2015. We haven’t seen quite the same clustering in autumn.”