Talking Point: When will the mountain burn?

DAVID BOWMAN: After 1967 and Dunalley, it’s hard to explain the ignorance of the potential for catastrophic bushfire in Hobart

HOBART is framed by kunanyi/Mt Wellington, which provides a superb backdrop to our city. It is an ancient presence, framing our daily lives, even sometimes affecting our moods.

But there is another, fierce dimension to the mountain. It is an organic volcano, which under the right circumstances, can erupt creating bushfires of remarkable intensity. At their height, these bushfires can inject smoke plumes into the stratosphere while generating extreme weather and releasing energy sufficient to shatter boulders and incinerate suburbs.

The British colonists had no conception that the forests on the mountain can, and have, sustained bushfires of such extraordinary intensity.

They were enticed by the magnificent anchorage that provided shelter from the wild Southern Ocean. Even the extraordinarily observant naturalist Charles Darwin failed to notice the importance of fire in the landscapes surrounding Hobart.

But the ignorance of contemporary Hobart residents of the fundamental place of fire in the environment, and the potential for a catastrophic bushfire, is less explicable.

The notorious 1967 bushfires that could have impacted the city centre, the 2013 Dunalley bushfire, and the prolonged 2019 bushfire season are all clear messages that the threat of bushfire cannot be ignored.

Describing the mountain as an organic volcano that can “blow up” is quite a claim. What is the scientific evidence for this seemingly needless exaggeration? What can we do about this risk? What lesson do the Tasmanian Aboriginal people, who co-existed with flammable forests for 35,000 years teach us?

Let me briefly answer these questions, drawing on nearly 40 years of my research.

At the outset, I must emphasise one key point: climate change is only part of this story, making a dangerous situation worse.

These is no question global heating is increasing the risk of bushfires in Tasmania, through more frequent extreme fire weather and more lightning ignitions. Nonetheless, risk of extreme fires is hardwired into the ecology of Tasmania.

Extreme bushfires are colourfully described as “blowing up” when they send up an enormous smoke column that punches through the atmosphere, sometimes into the stratosphere. The associated thunderhead can create lightning storms that start new fires, unpredictable powerful winds that shower embers ahead of the fire front creating fire storms.

Lightning storms start new fires. Flickr/frankieleon, (CC) BY

Such extreme coupling of bushfire and weather systems may seem like science fiction, yet they are science fact. Technically, they are known as pyro-cumulonimbus or a pyroCbs storm cloud. The pyro-cumulonimbus that developed from the 2003 Canberra fire generated a fire tornado that severely impacted suburbs.

The Dunalley pyro-cumulonimbus developed a cloud top that reached more than 10km into the atmosphere, sucking up burning debris that later showered down on the township, burning down much of that community, but thankfully causing no loss of life.

Pyro-cumulonimbus were once a global oddity, but they are apparently becoming more common, possibly due to climate change.

Recent research by Australian fire scientist Jason Sharples has identified four ingredients required to trigger pyro-cumulonimbus — heavy bushland fuels, rugged terrain, sustained winds and unstable atmospheric conditions.

Hobart location ticks all of those boxes. In a nutshell, Hobart is exposed to a formidable natural hazard.

Investing in more and bigger firefighting kit is a seductive response, but there are no known technologies that can quell a firestorm.

The only practical responses to the threat of catastrophic bushfire involves intensely managed use of fire and fuel loads. That is why under extreme conditions fires are banned, and any fire started under such conditions must be stamped on by firefighters before they become uncontrollable.

Managing fuel loads reduces the intensity of fire, increasing the opportunity for effective firefighting.

In a very real sense, we need to fight fires at least five years before they start!

This means modifying forests in the surrounds of Hobart to manage fuel loads and change their structure.

Our homes and gardens must also change. Buildings need to be built to reduce the risk of combustion and specifically designed to survive fire storms, and older housing stock must be retrofitted to conform to such building standards.

Gardens need to be re-designed to provide fire protection using plants with low flammability.

We need to acknowledge that Aboriginal people reduced fuel loads and limited the risk of massive wildfires through patch-burning the bush with lots of little fires.

Adaptation to the growing threat of bushfire will be neither straightforward nor easy. It is a big, costly, transformative community project. However, ignoring the likelihood and capacity of the mountain to fuel a catastrophic firestorm is simply not an option.

David Bowman is Professor of Pyrogeography and Fire Science and Director of the Fire Centre Research Hub at the University of Tasmania.

This opinion originally was published in Mercury on 13 August 2019.

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