10/02/2020

(AU) Climate Change Could Lead To Increase In Dangerous Firestorms That Were Once 'Rare'

Sydney Morning Herald - Laura Chung | Nick Moir

Scientists fear climate change will cause a once "rare and unique" weather event to become more common, as they race to develop predictive modelling and tools to help them better understand pyrocumulonimbus (pyroCB), commonly referred to as firestorms.
Jason Sharples, a professor of bushfire dynamics at the University of NSW, records the frequency of these storms around Australia and said between 1998, when relevant records started, and 2018, there were 62 confirmed pyroCBs.
But this bushfire season has seen that figure jump.
Lightning from a pyroCB storm breaks through while bushfires rage nearby. Credit: Nick Moir
Since September last year, at least another 30 pyroCBs have been recorded Australia-wide, while a further 15 possible storms are still being investigated.
"It's concerning, obviously, but I think this season comes down to extreme dryness and energy that the fuels were able to put out as they burnt," he said.
He notes that in previous years, the pyroCB pattern was irregular - with one or two events every three years or so, but recently these storms have increased in frequency.


Bushfires can create their own weather, generating ‘pyrocumulonimbus’ clouds and storms.

Professor Sharples is also a volunteer firefighter in the ACT and said he has been through an area ravaged by a pyroCB once. It was in the aftermath of the Black Saturday 2009 fires and he said the scene was "like a bomb had gone off".
"It was like a giant had taken a blow torch to it [the town]. You really get a moonscape feel," he said.

'Phenomenal increase'
A pyroCB event occurs when the intense heat from the fire causes air and smoke to rise and draws in cooler air.  If the air cools enough, the moisture in the plume condenses and forms a pyrocumulus cloud.
Under the right conditions, the cloud can mix with ice particles and cause lightning, producing a thunderstorm - known as pyrocumulonimbus.
The storms can cause unpredictable changes in fire behaviour, making it more dangerous for firefighters and nearby communities.
Fire researcher at the Bureau of Meteorology Mika Peace said over the past few decades, the knowledge about how fire and weather interact has increased.
"Since then, there's been a massive research effort in understanding pyroCBs and more recently predicting them," she said.
Dr Peace said in the 1950s and '60s, fire information focused on what was happening on the ground. Since then, scientists have turned their attention to what is happening above them too.
"This season has been unprecedented [for pyroCBs]... we've seen multiple pyroCBs developing on the same day over individual fires," she said.
In past fire seasons, these incidents were "rare and unique", said NSW RFS manager of the planning and predictive services unit Simon Heemstra.
But this season,  there has been a "phenomenal increase" in pyroCB events.
Dr Heemstra said one of the dangers of pyroCB events is the long-range spotting of fires up to 30 kilometres away from the main fire front.
Photographs show spot fires breaking ahead of the Clear Range Fire along the Monaro Highway on February 1. Credit: Dean Sewell
Other dangers include fire tornadoes, downbursts of air causing the fire to hit the ground and burst outwards and lightning which can cause new fires up to 60 kilometres away.
"Some days, state operations issued five or six alerts for different fires around the state because of pyrocumulus columns. [PyroCB] are a big concern. We'll be seeing more and more as a feature for the future," Dr Heemstra said.
Scientists note climate change will alter ground-level weather and the upper atmosphere, making conditions more conducive to pyroCBs. This risk highlights the need for more predictive modelling and tools.
At the moment, predicting where pyroCBs will hit is difficult, with the RFS erring on the side of caution as the consequences are too severe if something goes wrong.
The Herald's chief photographer Nick Moir, who has spent the last few months documenting the bushfires and their devastation, said he has been close to several pyroCB events this season, including a run-in at the Gospers Mountain fire.
Over this fire season, NSW experienced several pyroCB events, including during the Gospers Mountain fire. Credit: Nick Moir
"I was underneath it when it went pyrocumulonimbus, there was rain, hail and lightning all around the area. I was in a burnt-out area so I was safe, but there were strong winds, and, in particular, lightning ahead of the actual fire front and the storm," he said.
Former Tasmanian fire chief Mike Brown spent 39 years fighting fires and has only seen one pyroCB which was in the 2013 Dunalley fire, east of Hobart.
"It created strong winds and severe updraft, we had an aircraft working on that fire and they reported they had the worst turbulence they had ever experienced," he said.
"You’re organising tactics according to winds going a certain direction, but then suddenly [when the pyroCB occurs] there are unpredictable winds and weather patterns that are causing unpredictable and extreme fire weather conditions."
Mr Brown said at the time fire crews noticed burning material and embers being carried up high into the sky. Following the fire, they noticed scorched birds all along the beaches and believe they were burnt to death when the embers caught them unawares.
While this fire season has been marked by devastation, it provides a unique opportunity for scientists around the world to learn more about pyroCB events: what causes them, the safety risks associated with them and what they mean for the future of firefighting.

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