Covering climate now series: NZ's rising fire risk

Wildfires like the Pigeon Valley disaster (pictured) already cause enough damage to cost the economy around $67 million each year. That toll is set to soar under climate change. Photo / NZ Herald

Take a quick glance at maps colouring New Zealand's projected fire danger.

Today, the situation that rural firefighters like Rob Hands face isn't as bad as it could be.

Those places that have a higher number of days toward the riskier end of the dial are where you'd expect: Gisborne, Canterbury, the upper-eastern tip of the South Island.

Jump forward to 2040 and these coded yellow and red swathes expand to consume much of New Zealand. Then skip to 2090 and there isn't much of the country that's left green.

If you want to visualise what this might look like in reality, think back to the blaze that tore across 35km of Nelson's Pigeon Valley in February.

New Zealand's biggest wildfire in 70 years ravaged 2300ha of pine forest, razed a home and forced the evacuation of a town of 2500 people.

For the small army of firefighters who wrested it under control, it was tough, dusty, dangerous work. Charred roots underground could reignite; pits hidden by ash and soot presented perilous booby traps.

Last month, officials found the disaster had been caused by a tractor's plough in a stony, tinder-dry paddock, amid 28C heat, low humidity, blustery, warm wind and "extreme fire danger".

This graphic projects the annual frequency of Very High and Extreme forest fire danger across fire season months. Source / Scion

These conditions are considered abnormal now; a warmed world would make them increasingly common.

Rural fires already wreak enough damage to cost the economy around $67 million each year. But modelling showed almost all areas of the country would see an increase in fire danger, with the average fire season length increasing by about 70 per cent up to 2040 - and by about 80 per cent up to 2090.

Big droughts, too, would become an increasingly common occurrence, especially in northern and eastern areas of the North Island, and along the eastern side of the Southern Alps, with obvious implications for farming and water security.

By the end of the century, there could be more than 60 extra days over 25C in northern areas each year, and, even as soon as 2040, the average time in drought could double or triple.

Other research has suggested this scenario is somewhat here already: one study indicated that the $1.3 billion drought which hit the country in 2012-13 was 20 per cent more likely to have occurred than just over a century ago.

Although those typically dry regions of Gisborne, Marlborough and Canterbury would remain the most at risk of fire, the relative increase in risk was highest in Wellington and coastal Otago, where it could double and triple to 30 days and 20 days per season, respectively.

New Zealand's biggest wildfire in 70 years, at Nelson's Pigeon Valley, ravaged 2300ha of pine forest, razed a home and forced the evacuation of an entire town of 2500 people. Photo / NZ Herald

And several degrees of temperature rise, along with more and stronger westerly winds, doesn't just mean a greater number of fires, but a different type of fire.

What firefighters call "extreme fire" has dangerous features like spotting - where embers and other particles are hurled ahead of the fire front; fire tornadoes and whirls; and "blow-up" conditions, where the inferno suddenly escalates in size and intensity.

Up until now, there haven't been many cases of these volatile characteristics in New Zealand fires - one was a blaze that scorched 90ha of land near Hanmer Springs in 2016, another was this year's Pigeon Valley blaze.

But Hands, South Canterbury's principal rural fire officer, said it was something that crews would have to prepare for.

"We'd assume that we are going to have hotter and drier conditions, and longer seasonal periods."

Added to the threat was more fuel – dry grasses, brush and trees – that would drive more intense fires.

"We'd assume that we are going to have hotter and drier conditions, and longer seasonal periods," South Canterbury principal rural fire officer Rob Hands says. Photo / Supplied

"As soon as you push it, it can burn very quickly – both in terms of fire and distance."

Hands, a veteran firefighter of nearly 40 years, said extreme fires posed a particular danger to crews as they were harder to predict using normal models.

"That's why we are doing fire training all the time. We need to have a heightened awareness about what the potential for this fire is, and whether it can spread into something significant."

This story is part of the Herald's contribution to Covering Climate Now, an international campaign by more than 170 media organisations to draw attention to the issue of climate change ahead of a United Nations summit on September 23. To read more of our coverage go to nzherald.co.nz/climate