Testing how fire spreads

8 March 2018

Wildfires are becoming more frequent and severe as the climate changes. Scientists have researched fires for decades. They’ve built models that try to predict what a fire will do, but these models are unable to simulate the way extreme fires move and spread. Fires still behave in ways we don’t expect.

To understand more, Scion’s Rural Fire Research group is teaming up with the University of Canterbury’s Geography department and the US Forest Service’s Missoula Fire Sciences Laboratory as well as researchers from San Jose State University. Using harvested crop stubble paddocks near Darfield, this group of fire researchers are using state of the art fire behaviour sensors, meteorological equipment, and drones to test a new theory on fire behaviour.

“This science just wouldn’t be possible without collaboration. The University of Canterbury brings meteorological expertise and drone capabilities, and the Americans bring expertise and instrumentation that we don’t have here,” says Scion senior fire scientist Grant Pearce. “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. There are more than 25 scientists working together with private landowners to see if we can get some hard data around this new theory.”

Most current fire models are built on the idea that fire spreads through radiant heat transfer. This is the idea that the fire heats up the vegetation ahead of the flame front until it bursts into flames. This is what happens in your charcoal barbecue when the fire spreads from one coal bead to the next. Researchers from the US Forest Service have another theory that they would like to understand more. Their theory is that fire can also spread by convective heating. This is when a draft of air pushes the fire down onto the unburnt vegetation bathing it in flame. This would be like lighting your charcoal barbecue with a blowtorch.

Turbulence in the air causes updrafts and downdrafts that push the flame up and down. Understanding how all these 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 been seen in the lab using high-resolution imaging, but this series of experiments is testing it in the field for the first time. Researchers are conducting a series of controlled burns on stubble paddocks near Darfield over the next two weeks to measure the behaviour of fires under a variety of conditions. This is the first phase of a four-year burning programme. If conditions allow, they next plan to move to conducting tests in gorse scrub fuels.

Rural fires cost New Zealand around $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. 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.”