Bigger, wilder and more destructive: How cold fronts affected the Black Summer bushfires

World-first research conducted by Australian researchers has highlighted the role that cold fronts play in making bushfires drastically worse – posing a serious concern for future bushfire events.

Recently published research from UNSW Canberra and the Australian National University studied the impact of cold fronts during the devastating 2019-20 Black Summer bushfires, and found they increased dangerous bushfire conditions and led to bigger and more erratic fires.

By studying sea level pressure charts and the significant temperature drops associated with cold fronts, researchers determined that 46 per cent of the 50 large fire days during Black Summer coincided with cold fronts passing over southeast Australia.

UNSW Canberra Professor of Bushfire Dynamics Jason Sharples said while the relationship between bushfires and cold fronts may seem counter intuitive, it was important to understand the implications for future fire seasons.

“People often associate cold fronts with cooler temperatures and rain, so you might not think that would exacerbate bushfires,” Professor Sharples said.

“But before a cold front passes over southeast Australia, it will typically draw hot and dry northwesterly winds from Central Australia to the region. This can dry out fuels and lead to more dangerous fire weather.

“As the front approaches, winds get stronger and can abruptly change direction, which can change the size and shape of a fire front and lead to erratic fire behaviour.

“Cold fronts also lead to atmospheric instability which, when coupled with the extreme fire, can cause a pyrocumulonimbus, or fire thunderstorm. There were 44 of these events during Black Summer, more than we’ve ever seen in a single season before.”

The Black Summer bushfires were unprecedented in terms of size, intensity and destruction, sweeping across nearly 7.2 million hectares in southeast Australia. Evidence suggests the risk of extreme bushfire seasons, like the Black Summer, will increase in future.

It has been well established that the effects of human-caused climate change are leading to more dangerous bushfires, but the way that climate change might affect cold fronts and their impact on a bushfire season remains uncertain.

ANU Professor of Climate Science, Nerilie Abram said it was the first time cold front activity had been proven to exacerbate fires across an entire fire season.

“We had previously seen cold fronts escalate disastrous conditions during individual bushfires, but to prove it across an entire season is significant,” Professor Abram said.

“Twenty-three days during Black Summer saw large areas burn and also experienced a passing cold front, indicating that this association was a consistent pattern rather than coincidence.

“Our research also showed that the frequency and intensity of strong cold fronts were unprecedented in many of the areas that burned during Black Summer. This highlights the impact synoptic weather activity can have on bushfires.

“Importantly, our findings also showed that the extreme cold fronts experienced during the Black Summer were part of a long-term change in weather patterns over southeast Australia during the past 70 years.”

UNSW Canberra Associate Professor of Climate Science, Sarah Perkins-Kirkpatrick said destructive bushfires being exacerbated by cold fronts was a worrying trend for Australia.

“All the evidence points to worsening bushfire conditions in the decades ahead due to greenhouse gas emissions causing climate change,” Associate Professor Perkins-Kirkpatrick said.

“There is an increased likelihood of hotter and longer heatwaves, which could lead to greater drying out of fuel loads and more devastating bushfires.

“All of this combines to paint a pretty bleak picture of what is to come.

“This research again highlights the urgent need to limit and reverse the effects of climate change to reduce the chance of extremely dangerous and deadly bushfires.”

This research was funded by the Australian Research Council Centre of Excellence for Climate Extremes and was conducted in collaboration between UNSW Canberra and the ANU.

For more information please visit the following websites:

• UNSW Canberra Bushfire Research Group
• ANU Research School of Earth Sciences
• ARC Centre of Excellence for Climate Extremes

This research was published in Environmental Research Letters.

Media contact:

Elliot Williams,
UNSW Canberra Media,
Phone: 02 5114 5149
Email: elliot.williams@adfa.edu.au