6 February 2018
Victoria’s Fire Behaviour Analysts (FBAn) use grassland curing maps to predict the spread and intensity of a bushfire.
Rachel Bessell, who takes up the role of an FBAn in the State Control Centre says the maps use satellite imaging as well as intelligence from ground observers to display how dry the grass is across Victoria.
The dryer the grass, the faster the spread, she says.
“When the curing map is showing zero per cent cured, it means it’s lush, green grass. Typically a fire will self-extinguish at zero,” Ms Bessell said.
“It goes up in 10s, and 100 per cent is fully cured which means the grass is bleached, dry and holding very little moisture.”
As well as being able to make tactical decisions around planning and containing a fire, she said these predictions are also crucial in providing timely advice messages and warnings to communities.
“It’s not just strategic operations, it’s also for warning the communities,” Ms Bessell said.
“We can have a look at potential consequence areas, which is also used for community warnings so if we can understand the potential impact zone we can highlight that area and use that for our warnings as well.”
Anything above 50 per cent will start to burn quickly, so FBAns will be keeping a close eye on areas with a high curing rate, which at this time of year is most of Victoria.
“When we’re getting up towards 70 per cent we’re getting much faster rates of spread, so it makes containment of fires more difficult,” she said.
“The only place that’s not fully cured is West and South Gippsland. They’re sitting on about 50 per cent cured because often we get more sea breeze effects there and it’s also a bit more humid.”
Humidity can supress fire spread because the fuels aren’t as available.
“Grass fires in particular are very wind-driven so elevated winds on a hot day are a problem,” she said.
“When the winds are slower and it’s more muggy and humid, people are more uncomfortable, but fires generally don’t have the same spread.”
The grassland curing map is collated by a mix of community members who have registered as on the ground observers, and a satellite-derived model that looks at the amount of chlorophyll and water content in the grass.
“We really do need that ground truthing of human eyes to actually go out and see if it is dryer than the satellite’s suggesting,” Ms Bessell said.
“Satellite models have limitations, for instance they can’t see through cloud… and other issues that are species dependant.
“Flowering canola means it is partially through its drying cycle, but because of the bright yellow leaves the reflectance value changes with the satellite and it’s showing it as fully cured when really it’s in the green phase.”
While most current grassland observers are fire brigade members, anyone can become an observer.