New theory on fire spread tested

It’s a hot, windy February day - perfect conditions for fire. Twenty-seven scientists and several million dollars of specialised equipment are gathered in a paddock of harvested wheat stubble near Darfield, Canterbury, New Zealand.

As Jason Forthofer from the US Forest Service’s Missoula Fire Sciences Lab counts down to ignition, the researchers are all hoping the burn will bring the same thing: data. They will use this data to help unlock the mysteries of fire behaviour and produce better models for fighting wildfires.

This is the first phase of a four-year burning programme that will test a new theory on fire spread. It’s a collaboration between Scion’s Rural Fire Research Team, the University of Canterbury, Missoula Fire Sciences Lab and San Jose State University’s Fire Weather Research Laboratory. The new theory was developed in the US Forest Service lab in Missoula, Montana, but this is the first time it’s been tested in the field.

Researcher Mark Finney from Missoula explains, “For decades, the conventional wisdom was that fire spread by radiated heat. We’ve done some tests that show fire spreads by convection - hot gas and flame that moves through the wind. We’re trying to understand how that works and it’s a challenging problem that involves not only heat transfer but also fluid mechanics and weather - we’re trying to understand how all of these factors combine to allow a fire to spread.”

“This science just wouldn’t be possible without this collaboration,” says Scion senior fire scientist Grant Pearce. “The University of Canterbury brings meteorological expertise and drone capabilities, and the Americans bring expertise and unique instrumentation that we don’t have here.”

As the stubble fire is ignited and sweeps across the paddock, the researchers are pleased to see the flames move past their sensors as planned. Most of the equipment has been designed and built by the people looking on. The Scion team has organised the field research and has their own sensors laid out in the paddock and weather towers reaching up to record atmospheric details.

From a cherry picker just north of the paddock, University of Canterbury Geography researcher Marwan Katurji is looking after three infrared cameras, which are measuring the surface temperatures before, during and after the burn. A fixed-wing and quadcopter drones capture images that measure how fast the fire is moving.

A couple of hundred meters away, researchers from San Jose State University are sitting in the shade of a van, monitoring the Doppler LIDAR machine they have brought all the way from California. LIDAR stands for Light Detection and Ranging. It’s like a radar that uses reflected light instead of sound waves. The LIDAR data will show the air movement above and around the fire.

It’s been a long hot day, but as the researchers pack their equipment away, they are pleased. “Everything’s gone really well,” says Jason. “At least half the burns were almost perfect. We’re getting great data.”

Rural fires cost New Zealand around NZ$100 million per year and, more importantly, they affect people’s lives. Scion Rural Fire Research team leader Tara Strand explains why this research is important to New Zealand. “Extreme fires are becoming more common in New Zealand, so we need to be prepared. The better we understand fire spread, the better we will be at preventing the leap to extreme fire behaviour.”

Photo: A member of the Scion fire research team observes fire spread during one of the stubble experimental fires.

Source: Forest Health News, Scion, March 2018

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