What makes Australian bushfires so dangerous?
21 October 2013
Parts of Australia are prone to intense, uncontrollable fires that can have the same intensity as severe thunderstorm activity. University of Newcastle meteorologist Martin Babakhan explains to SBS what scientists call "extreme fire behaviour" and the characteristics that make it particularly dangerous.
By Rhiannon Elston
SBS: What is extreme fire behaviour?
Martin Babakhan: In Australia, we've been monitoring fire for years. We've come to the conclusion there are two types of fires. One is predictable behaviour. Fire-fighters could control it [easily]. The other one, we call the 'blow-up' fire situation. The energy of that fire is so intense it's uncontrollable. It's equivalent to severe thunderstorm activity, that's how dangerous it is. This fire tends to burst, moves faster than any other fires. That's the reason we have 200 properties just burn within so many hours.
How do meteorologists and firefighters identify it?
The most important element for [the Blue Mountains] fires was humidity. If the humidity was about sixty-five per cent I would say we cannot have a severe fire but if it is below sixty per cent humidity the fire becomes very severe. Severity of fire is determined by humidity and the instability of the atmosphere, as well as wind speed and terrain.
What are some of the characteristics of extreme fire behaviour?
Crowning: Extreme fire behaviour results in crowning whereby the fire reaches 100 foot at the top of the trees. If you are looking at it, suddenly another fire emerges above the existing fire like a cloud.
Prolific spotting: When that fire develops with a crown, the next stage is the wind. The wind vector becomes very important. The wind once it reaches to the core of this intense fire, it tends to develop a rotation. We call it a vortex. Once the vortex develops within the fire, that fire tends to tilt within the vortex. Once it reaches that height, instability plays an important role. The air mass starts heating up, and starts pushing in the upper atmosphere, and becomes very, very convective – it keeps going up.
Fire whirls: As the fire moves over the mountains, once it descends down the lee side of the mountains and comes down, [it] develops turbulence. That turbulence is connected to the whirls and becomes very dangerous.
What is it about the environment here in Australia, particularly in the southeast, that appears to be conducive to these very destructive fires?
We have structured our land in such way with national forests, vegetation, and a lot of rain one season which dries up and becomes fuel. Spring is the trigger of the fire in Australia because they tend to drag the dry continental air mass from Central Australia with North Westerly's which dry out the land.
What do you think we can expect to see as we move towards summer and those hotter days?
This early fire season onset will not alleviate fires into summer. Northern and Southern tables are susceptible to fire risk. We are in a severe fire season. We're looking at the weather patterns and rain is the most important element. The first of November is the transition season where the equator plays an important role in our climate. The equator tends to bring monsoons close to Australia with rain and storms and so on, so we are going to get some rain but what is the intensity? We are going to get mostly thunderstorms which generate lightening – a fire trigger.<
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