Rising risk: What scientists just learned about NZ’s ‘extreme fire’ danger

Media were taken through Lake Ōhau village by Fire and Emergency Incident Controller, Graeme Still, to see the damage from the devastating fire. Video / Logan Church

The same extreme conditions that led to the catastrophic wildfires of Australia’s “Black Summer” can form in parts of New Zealand – and more frequently than experts first thought.

That’s according to just-published modelling that raises troubling implications for Kiwi communities living near pine forests – and also for the Government’s billion-tree planting plan to curb climate change.

Rural fires already wreak enough damage to cost the economy around $67 million each year – 2019’s Pigeon Valley blaze and the following year’s Lake Ōhau disaster being two dramatic examples.

That danger will only grow as our planet continues to warm, with projections indicating notable fire seasons on average increase in length by 30 per cent by the end of the century.

Whether New Zealand also faced the risk of the most extreme wildfires – so-called “very extreme” events – is something climate scientist Dr Nathanael Melia and colleagues have been exploring with a sophisticated new model.

It combined Niwa’s latest regional climate data with the Canadian Fire Weather Index (FWI) algorithm, which considers a range of factors to predict a fire’s intensity.

The FWI also assigned a numerical rating to different fires, from typically small and easily-contained rank ones and twos, to unpredictable, self-sustaining rank fives and sixes that sweep through forest canopies and drive their own weather.

“Typically, a destructive fire in New Zealand – such as Port Hills, Pigeon Valley, and Lake Ōhau – are rank four, and occasionally we might get a rank five,” he said.

“So, we knew that these fires can occur, but we wanted to ask, will they become significantly more frequent? To answer this we turned to our pioneering technique of climate emergence.”

Unsurprisingly, the general picture worsened under likely climate change scenarios for this century.

“Widespread emergence can be avoided, but some degree of emergence is already baked in for parts of the country.”

They were soon surprised to find the conditions to create very extreme conditions equivalent to above rank six had already been observed here.

This map shows areas of New Zealand where conditions that led to Australia’s “Black Summer” wildfires of 2019-20 has already occurred based on path observations – and where it could in future, with return periods colour coded. Source / Nathanael Melia, Victoria University

Melia happened to be part-way through the analysis, and working at research institute Scion, when Australia’s unprecedented bushfires tore across the country in 2019.

“We knew that the bushfires that occur in Australia were far larger and more severe than those we get over here,” he said.

“Australia has a continental-sized desert that can provide blast furnace conditions upwind, while we have the Tasman that is comparatively an air conditioning unit.”

Still, he thought it’d be prudent to plug the fire weather values behind Australia’s calamity into detailed projections he and colleagues had developed for New Zealand.

“I wasn’t expecting to find any hits, or, at worst the occasional match at the end of the century under the worst-case scenario climate conditions,” he said.

“I was right to check, but very wrong in my expectations.”

The data turned up plenty of positive matches in the projections – but also in recorded observations from just the past few years, when similar conditions had formed in parts of Central Otago and the Mackenzie Basin.

This map shows areas projected to experience emergence in the season length of wildfire weather risk, up to the specified wildfire rank severity from 2005 to 2020 levels, to 2100. Shaded areas also include all wildfire ranks below. “Rank one” fires are the smallest and most containable, while “rank five” and “rank six” fires are the largest and most dangerous and unpredictable. These maps are shown across over four Representative Concentration Pathway (RCP) climate change scenarios for New Zealand, with RCP 2.6 showing a low-emissions world – and RCP 8.5 showing a high-emissions one. Source / Nathanael Melia, Victoria University

While these areas proved to be the most at risk of “very extreme” fire, with conditions occurring around every five years, the modelling also highlighted other potential hot-spots, such as Marlborough, where the conditions emerged every five to 20 years.

“There were also larger areas that occurred about one in 100 years.”

At the same time, however, it was still possible for very extreme conditions to occur even without the hand of global warming.

Melia likened climate change’s impact severe wildfires to loading one of three dice, but trying to roll sixes on all of them. However, with very extreme wildfires we’re loading one of 10 dice.

“The effect of that weighted dice is less important than the overall randomness of the phenomena.”

In any case, he said companies running forestry – and communities living around them – needed to be prepared for the rising risk of fire.

“Large forestry organisations such as those in the Central North Island are well placed in a lower risk zone, employ specialist fire experts and even have their own rural fire service,” he said.

“However, those smaller plantations in more high-risk zones such as Hawke’s Bay, Marlborough, Canterbury, and Otago face greater challenges.”

Given the forestry sector annually contributed about $6 billion to our economy, while also sequestering millions of tonnes of carbon and offering stable investments for pension funds, he saw risk-planning as all the more urgent.

Australia’s “Black Summer” bushfire season of 2019-20 caused 34 deaths, cost more than $100 billion in damage, and ended with 24.3 million ha of burnt land. Photo / AP

“The Government has a planting programme and carbon farming has really taken off as venture capital invests in the price of carbon,” he added.

“While afforestation and reforestation are beneficial from a climate mitigation perspective, planting in the highest risk areas should be done with caution – and certainly far removed from people and infrastructure.”

He noted there were many settlements already perched on the urban-rural interface – sometimes located on steep hillsides and with few access routes.

“They are beautiful places to live, and you see them everywhere as you travel the country, from Queenstown to Wellington – they’ve never had a wildfire and it doesn’t register as a threat,” he said.

“But it is – and all that’s needed is the right combination of weather conditions, and ignition source.

“These areas need to be identified and the people that live there need to have a plan – just like we do for tsunami and earthquakes.”