30 Jan 2020

The science of wildfires

From Our Changing World, 9:06 pm on 30 January 2020

Fire scientists say New Zealand wildfires will increase in frequency and severity, and they are concerned that many people are underprepared.

A firefighter walks past burning trees during a battle against bushfires around the town of Nowra in the Australian state of New South Wales on December 31, 2019.

Photo: AFP

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When you look at images of the giant fires which have swept across Australia this summer, you’re looking at what scientists call “Extreme Fire Behaviour”.

Normal bushfires usually travel through the undergrowth. They burn scrub and leaf litter, and scorch the trunks of trees. 

Extreme Fire Behaviour is very different: walls of flame engulf entire trees, superheated air currents create fiery tornadoes called fire whirls and loft burning embers hundreds of meters to start new blazes downwind. 

These kinds of fires are often impossible to extinguish using conventional tactics. Sometimes the best that can be done is to protect a few key locations and evacuate everywhere else. 

New Zealand has sometimes seen itself as immune to this kind of fire, but that’s a potentially deadly mistake. 

“We need to be concerned that our communities do not think that wildfires occur in Australia and not our own country,” says Lisa Langer, lead social scientist at the Scion Rural Fire Research Group.

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Photo: AFP

Closer to home

You may have missed it, but at the exact same time as the blazes in Australia were reaching their peak, New Zealand also saw one of its biggest wildfires in 20 years.

“This was a big tussock fire near Dunedin,” says Grant Pearce, senior fire scientist in the Scion Rural Fire Research Group.

“It burned more than five thousand hectares … burned for multiple days and involved large numbers of firefighting resources.”

We also saw extreme fire behaviour in the 2017 Port Hills Fire and the 2019 Pigeon Valley Fire near Nelson.

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Photo: AFP

Grant Pearce says we can expect to see more of these kinds of fires due to climate change.

“We’re going to see increasing temperatures, changing rainfall patterns with less rainfall in eastern parts of the country and also stronger westerly winds with potentially lower humidity. So you combine all of those effects and that means we will see increased fire danger in many parts of the country.”

Currently the regions most at risk of wildfire are Northland and the top of the South Island; both of these areas are likely to see more frequent and more intense wildfires in the future. 

But Grant Pearce says the biggest jump in fire danger is likely to be in places which have not typically seen large bushfires in the past, including northern and coastal Otago, Wairarapa and Whanganui.

“We could see a doubling or even trebling of the number of severe fire weather days [in those areas],” he explains.

A burnt vehicle on Quinlans street after an overnight bushfire in Quaama in Australia's New South Wales state on January 6, 2020.


Fire preparedness

Another fire researcher at Scion, Dr Tara Strand, says many New Zealanders are underprepared for the risk of wildfire. She says this is particularly so for those in suburban or lifestyle properties near the rural/urban boundary.

“There is still the mentality that ‘if [a wildfire] enters the suburban environment I have faith the fire trucks will come and put it out’.”

Tara Strand says that this attitude has contributed to several deaths in wildfires overseas, where firefighters were unable to contain a wildfire and people failed to evacuate quickly enough. 

Lisa Langer has been researching the awareness of fire danger in these at-risk communities. 

“There are two things. There’s the awareness [of risk], but then there’s also the question of whether the awareness turns into preparing for the fire.”

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Photo: supplied

Limitations of current fire danger signs

Lisa Langer says traditional wildfire messages have focused on alerting the community to the risk through rainbow-coloured fire danger signs and encouraging people to call 111 if they see smoke or flame. But her research has found that these tactics have their limitations.

“People understood there was an increase in danger as the arrow moved from left to right. But in terms of how they should respond and what behaviour they should undertake, that’s where difficulties lay,” she explains.
Lisa Langer says part of the problem is that people didn’t know at what point on the scale they should stop doing potentially risky things like lighting campfires or preparing hangi. Also, they struggled to understand how much the risk of fire was increasing by between each level.

“It’s not a linear scale, it’s probably more of an exponential scale,” says Grant Pearce. “As the fire danger level increases, the potential severity and consequences increase dramatically.”

A bushfire burns outside a property near Taree, 350km north of Sydney on November 12, 2019.

Photo: AFP

Listen to the full Our Changing World podcast to hear how New Zealand scientists are working to improve the modelling of wildfires, and how Mātauranga Māori can be harnessed to reduce the risk of wildfire.

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