Scientists will send drones above burning fields in rural Canterbury this month to learn more about one of climate change's biggest future threats: extreme fire.

Rural fires cause about $100 million in damage to the country each year.

But what are called "extreme fires" have rural fire authorities more worried, as their unpredictable and dynamic conditions could put firefighters at greater risk, particularly if the fire spreads behind them.

Conditions that increase extreme fire risk include mid to high temperatures, low humidity and wind speeds gusting at 50km/h to 70km/h.


These include 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.

Cases of extreme fire behaviour have already been seen in some smaller blazes and in conditions where it wasn't expected, including a fire that devastated 90ha near Hanmer Springs in 2016.

Under climate change scenarios projected to deliver several degrees of average temperature increase and stronger and more frequent westerly winds, the number of extreme fires will double or treble by the end of the century - perhaps even by 2050.

Population growth, more people moving to rural areas, and a changing landscape bringing different fuel sources, such as wilding pines, will add to the threat.

In a new research project, scientists from Crown research institute Scion have teamed up with experts from the University of Canterbury, San Jose State and the US Forest Service's Missoula Fire Sciences Laboratory.

Scion scientists have been able to better understand fires through
Scion scientists have been able to better understand fires through "controlled burns". Photo / Supplied

Using harvested crop stubble paddocks near Darfield, the researchers will use state-of-the-art fire behaviour sensors, meteorological equipment and drones to test a new theory on fire behaviour.

"New Zealand fire research is known globally for its long history of collaboration but this is unprecedented in my 25 years on the Scion fire research team," Scion senior fire scientist Grant Pearce said.

"There are more than 25 scientists working together with private landowners to see if we can get some hard data around this new theory."

The work aims to test a particular theory around extreme fire.

Most current fire models are built on the idea that fire spreads through radiant heat transfer, where the fire heats up the vegetation ahead of the flame front until it bursts into flames.

This can be observed in charcoal barbecues, when fire spreads from one coal bead to the next.

The unpredictable and dynamic conditions of extreme fire can put crews at greater risk. Photo / File
The unpredictable and dynamic conditions of extreme fire can put crews at greater risk. Photo / File

But another theory the researchers are interested in is convective heating - where a draft of air pushes the fire down onto the unburnt vegetation bathing it in flame, something akin to lighting a charcoal barbecue with a blowtorch.

Turbulence in the air causes updrafts and downdrafts that push the flame up and down, and understanding how all the elements work together will allow more accurate fire spread models that could save lives, homes and natural resources all around the world.

The theory has already been observed in the lab using high-resolution imaging, but this series of experiments is testing it in the field for the first time.

After the Darfield tests, further experiments are planned in gorse.

"Extreme fires are becoming more common in New Zealand so we need to be prepared," Scion Rural Fire Research team leader Tara Strand said.

"In other parts of the world, extreme fires have the space to burn themselves out but as a comparatively smaller country, we don't have that space.

"There are important species and ecosystems, people, buildings and other assets such as forestry that are threatened by any large fire here.

"The better we understand fire, the better we will be at stopping them."

Scion has received an $8.5m grant from the Ministry of Business, Innovation and Employment's Endeavour Fund to study extreme fires.