Bushfires in south-west WA impacted by global trend of drying Mediterranean climates

26 February 2021

Published by https://www.abc.net.au/

AUSTTRALIA – In the wake of the recent Wooroloo bushfires in Western Australia, fire experts have warned a long-term reduction in rainfall in the state’s south-west is making blazes there worse.

Key points:

  • Serious bushfires are becoming more frequent in south-west Western Australia
  • The increased frequency of serious fires is linked to a drying trend in the region
  • Droughts and bushfires are increasing in Mediterranean climates around the world

“I think serious fires have become more frequent,” said Murray Carter, executive director of the Rural Fire Division in WA’s Department of Fire and Emergency Services (DFES).

“Those which you characterise as causing damage to property or worse, human fatality, which we obviously don’t want to see.

“Two decades ago we would’ve had those fires maybe once every five or six years, now we get them every two or three.”

Fire season extending as winter rains shrink

According to the Bureau of Meteorology, the south-west corner of Western Australia has seen a 20 per cent reduction in winter rainfall since the 1970s due to climate change.

Much of the decline in rainfall has occurred during the autumn and early winter months (April to June), according to Lachie McCaw, the principal research scientist with WA’s Department of Biodiversity, Conservation and Attractions (DPCA).

“It means that dry conditions, conducive to fire ignition and spread, may persist for the first half of the year,” he said.

“Fire seasons are extending longer into the autumn and in some years are beginning a month or more earlier than was typically the case a decade or two ago.”

Dr McCaw said a shorter, drier winter rainy season was leading to drier, more combustible fuels in the summer fire season.

“When warmer conditions return during the spring, large dead woody material ignites readily,” he said.

He said declining autumn rains were extending the fire risk into winter.

“We have experienced several events of widespread bushfire activity in late May and early June in the last few years,” Dr McCaw said.

“These events have resulted from the coincidence of persistent dry fuels conditions and strong pre-frontal winds associated with early winter cold fronts.”

map showing Western Australia having above average fire potential

This summer, parts of south-west Western Australia had above average fire potential due to dry conditions.(Supplied: Bushfire and Natural Hazards CRC


Drying trend a worldwide phenomenon

The drying trend in south-western Australia is part of a pattern of reductions in winter rains around the world, according to Pandora Hope, a climatologist with the Bureau of Meteorology.

She said the trend has been affecting temperate regions which have wet winters and dry summers — the so-called Mediterranean climates.

“We’ve seen similar declines in southern Africa and South America,” she said.

Chile experienced what became known as the megadrought over the past decade, with a 30 per cent reduction in rainfall there.

The Western Cape region in South Africa has recently recovered from the Day Zero drought that saw Cape Town nearly run out of drinking water in 2018.

Dr McCaw said there was a global pattern of increased fire activity in Mediterranean climates.

“Looking back over the past five years, there have been damaging bushfires in the western US, Chile, South Africa and Mediterranean European countries including Greece, Portugal and Spain,” he said.

“The south-west of WA has also experienced some damaging bushfires, most recently at Wooroloo and also at Yarloop in January 2016.”

Climatologists believed the drying trend in these Mediterranean climates was being partly driven by winter storms tracking further south, due to the effects of climate change.

“As you get an expansion in the tropics and more high-pressure systems over the region, it just makes it that much harder to rain,” Ms Hope said.

“There are changes to the fronts that come across the region that normally bring rainfall; we’re seeing a decline in the number of them, but also decline in the amount of rainfall that comes from them.”

map showing subtropical ridge moving south in winter

Climatologists have linked south-western Australia’s drying trend to an expansion of the subtropical ridge.(Supplied: Bureau of Meteorology


Adapting to more fire

Mr Carter said West Australians could adapt to the changes by being more proactive.

“We talk a lot about community resilience, but we also need to talk about landscape resilience, and that’s about using fire in the landscape,” he said.

Dr McCaw said the biggest fire threat in south-western Australia was from large-scale, high-intensity bushfires burning during the summer dry season.

“Attempting to exclude fire on a broad scale will lead inevitably to this outcome and put the community and the environment at significant risk,” he said.

“The approach that continues to be used in WA by the Department of Biodiversity, Conservation and Attractions, Parks and Wildlife Service is to use fire wisely through prescribed burning.”

The silhouette of a man, dressed in full PPE, looking to the tree tops.

DBCA scientist Lachie McCaw assesses the Manjimup prescribed burn.(ABC RN: Fiona Pepper

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