The prediction of a hotter-than-average summer has led to an update of the national bushfire outlook, with Australia’s most highly populated areas – including regions around Sydney, Melbourne and Hobart – facing an above-average fire risk.
The stark exception is Queensland and north-eastern New South Wales, where the wettest October since 1975 has led to a downgrading of the fire risk for the coming summer.
However, Dr Richard Thornton from the Bushfire and Natural Hazards CRC said recent rains had not been enough to reduce fire potential.
“The long-term rainfall deficit has seen a lot of the forests starting to dry out,” he said.
“That’s why, if you look at a lot of the areas that are still at high risk of fires, they’re forested areas.”
Dr Thornton said that was combined with the equal warmest May to October period on record.
“Over the last couple of months we’ve actually seen above average temperatures,” he said.
“In fact, we’re seeing it quite extensively at the moment through south-eastern Australia.
“That would have exacerbated the drying of the subsoils but also helps with the vegetation growth.”
Queensland, New South Wales, Victoria and Tasmania have experienced significant fires already this season.
“We’re now already in the fire season [so] it’s now we have to think, ‘What are we going to do when and if the fires come?'” Dr Thornton said.
“It’s too late when you get the warning on your mobile phone about the fire down the slope from you.”
Hotter summer predicted
Climate models are predicting a hotter than average summer, despite the likelihood of a La Nina weather pattern normally associated with cooler and wetter conditions.
A cooling of the Indian Ocean is bringing drier conditions across much of Australia, cancelling out the influence of La Nina.
“People might be hearing from the Bureau [of Meteorology] about La Nina, thinking, ‘Oh, it’s going to be wet’, Dr Thornton said.
“Don’t forget, we have had significant fire activity in La Nina years.”
The Black Saturday bushfires of 2009 took place during a weak La Nina.
Senior climatologist with the Bureau of Meteorology (BoM), Dr Blair Trewin, said on Tuesday that there was an intriguing link between weak La Nina years and heatwaves along the southern and south eastern coastline.
November heat wave
Although La Nina has not yet been officially declared, south-eastern Australia is currently experiencing a prolonged heat wave.
Dr Trewin said it was being driven by a slow-moving high pressure system over the Tasman Sea.
“What we’re seeing now is a very prolonged heat spell, more of the type more typical of late summer or early autumn,” he said.
Below is a synoptic chart from the last few days show the blocking high in the Tasman Sea
“What we’re expecting to see is unprecedented for spring or early summer.”
Melbourne has now had nine nights in a row above 15 degrees Celsius with Dr Trewin saying the city had never had more than nine nights a row above 15 degrees Celsius earlier than January.
“We’re seeing conditions in Melbourne which would be more typical, at this time of year, [to] northern New South Wales or southern Queensland,” he said.
The same high pressure system breaking records in the south-east of the country is bringing persistent cool temperatures to Queensland and northern New South Wales.
Dr Trewin said Armidale in northern New South Wales had not had a day over 22 degrees Celsius for two weeks, which was also heading towards record-breaking territory.