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More than climate change driving Queensland fires, explain climatologists

By Ben Deacon and Penny Timms, Tuesday September 10, 2019 - 05:58 EST
Audience submitted image
The negative Southern Annular Mode affecting Australia is set to make conditions difficult for firefighters. - Audience submitted

The record drought has combined with a record warm winter to fuel this year's grim fire outlook, according to climatologists and bushfire experts.

"The forests are in a state where even a small ignition source can cause major problems," warned Richard Thornton from the Bushfire and Natural Hazards Cooperative Research Centre.

"And that will only get worse as we move into summer and things dry out even further."

Andrew Watkins from the Bureau of Meteorology says the southern half of Australia has experienced the driest January to August on record.

"When we take into account temperatures as well, which have been highest on record for winter in some of those bushfire areas, we've had high evaporation," he said.

"We have very dry soils and dry fuel as well."

, the dry conditions have been driven by cooler than average waters in the Indian ocean, which meteorologists refer to as a positive Indian Ocean Dipole, or IOD.

Pacific ocean temperatures are not driving , with no El Nino or La Nina expected to develop in the coming months.

There is another, less well-known climate driver behind the strong westerly winds fanning the flames.

"We have a period of negative SAM (Southern Annular Mode) affecting us now, as it has on and off for a while," Dr Watkins said.

When the SAM is negative, strong westerly winds like the ones experienced at the weekend reach further north than normal.

What's driving the fire season ahead?

The warm, dry conditions that have led to the early fires are predicted to continue for the rest of the year.

"Unfortunately, the odds are high of having above normal daytime temperatures right through at least until January," Dr Watkins said.

"And likewise with rainfall, there are increased odds of drier than normal conditions for much of eastern Australia right through until January as well."

On top of this, the recent is predicted to keep SAM negative for the rest of the year, reinforcing the warm, dry conditions in New South Wales and southern Queensland.

Climate change trends

"Climate change is playing its role here, but it's not the cause of these fires," Dr Thornton said.

"We're seeing a degree on average higher temperatures than the long-term average."

Climate change expert Andrew King from Melbourne University agrees.

"It's quite clear that the type of hot weather associated with bushfires is becoming more frequent and more intense and it's also more likely to occur earlier on in the warm season," he said.

But the climatologist said the story is more complicated when it comes to rainfall.

"There's not really a very clear trend," Dr King said.

"Overall, we don't really see a clear trend towards more dry conditions or more wet conditions [in southern Queensland].

"We have really highly variable rainfall in eastern Australia, linked with things like El Nino and La Nina, and also individual weather systems."

But he says further south, drought is linked to climate change trends.

"In the south west of Australia, and in parts of Victoria, there is a decreasing trend in rainfall. Which obviously worsens bushfire conditions, overall, on average."

And when it comes to increased westerly winds like the ones that fanned this week's fires, he said climate science predicts less strong winds.

"The general climate trend is towards more positive SAM conditions, which means that we see those weather systems moving further south away from Australia and associated with that, we wouldn't see the same frequency of westerly winds that we've seen recently in New South Wales and Queensland."

Fire danger on the rise

The Bureau of Meteorology's state of the climate report from last year showed the overall fire danger index had increased over the past 40 years over much of southern Australia.

Dr Thornton expects this trend to continue.

"What climate change will do is it will increase the frequency, or the return rate if you like, of really bad fire weather days," he said.

"So the days like where you had Ash Wednesday or black Saturday, the return period for those sorts of days, will come back and will become shorter.

"So we really need to start thinking about how do we prepare properties better for that?

"How do we make sure that communities stay safe?"


© ABC 2019

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