CLIMATE change is impacting fire behaviour, says RFS volunteer David Edworthy, from Windellama, 40km south east of Goulburn.
Scientific inquiries into bushfire events, mostly carried out since the 2003 Canberra fires, have placed greater emphasis on factors other than ground fuel that drive a fire, he said.
A recent phenomenon of extreme “pyroconvection” bushfires, leading to “pyrocumulonimbus” (Pyro-CB) burns, are more influenced by the atmosphere and terrain, he said.
“There have been some 25 Pyro-CB fires in Australia in as many years with a sharp increase in regularity since 2003,” he said.
“This is a worldwide trend: it’s not just happening locally.
Fires are getting larger, more intense and occurring more often.”
With greater research comes greater knowledge of how to read warning signs, interpret conditions and respond.
“Up until the Canberra fires, most bushfire behaviour modelling was done using observation.
There was little science behind it at all. The whole game has changed,” Mr Edworthy said.
“They are starting to do the physics on fire behaviour ... the two big things that have come out of the research is how much the upper atmosphere ... and the topography of the land influences fires.”
The Goulburn Garroorigang Road blaze on November 20 was an example of this, he said.
The grass fire burnt some 60ha, closed the Hume Highway for hours, and took more than 130 land and air emergency personnel to contain.
“On the day, the prevailing westerlies were blowing across the hill near McDonalds, causing the wind to vortex, pushing the fire in a northerly direction,” he said.
“The local RFS crews did an outstanding job in stopping the fire before it [reached] the Gundary plains, which could have been disastrous, given the low humidity and high wind speed.”
He stressed that residents in bushfireprone areas must continually check the fire danger index (FDI).
“What makes it all-important is the changing nature of the climate, and how severe these fires are becoming,” he said.
“That’s why we get these rapid drying events where the day can go from just an average bushfire day to an absolutely horrendous day.
“The important part is we’ve now got three weather stations around the place and have calculated data into a single figure of FDI.
“At 80 FDI, in extreme conditions ... we really can’t stop a fire, so we are trying to encourage the public that, even if there is no fire in the area, [to] enact your bushfire survival plan.
“Conditions can change dramatically ... and all of a sudden.”