They’re as familiar to Australians as a stop sign: the semicircular, multicoloured warning signs that indicate the level of danger posed by bushfire on any given day. But after more than half a century of use, the Australian fire danger rating system is being completely overhauled to bring it into line with advances in fire science, community behaviour and climate change.
From September 1, the new fire danger rating system will be consistent across all states and territories, with only four levels instead of six. The modelling that informs the ratings can easily be updated as the science and modelling of fire behaviour evolves, and will hopefully improve the accuracy of forecasting to reduce the risk either of false alarms or – the worst-case scenario – missed warnings that cost lives.
Apart from the introduction of catastrophic/code red after the 2009 Black Saturday bushfires, the ratings haven’t changed much since they were first devised by a CSIRO fire scientist, the late Alan McArthur, says Alen Slijepcevic, deputy chief officer of the Country Fire Authority in Victoria.
“The old system that was designed in the ’60s was never expected to last that long, and it wasn’t designed for the purpose that we extended its use for,” Slijepcevic says. “If you go back to the original work of McArthur, he designed it based on difficulty to suppress fires, and anecdotally that was based on the amount of swearing coming from the crews.”
The previous fire danger categories were based on McArthur’s Forest Fire Danger Index (FFDI). This is an open-ended scale based on measures of air temperature, wind speed, humidity and the dryness of the vegetation. Each of the six fire danger ratings corresponds to a range of scores and a colour that denotes the level of warning, from low/moderate at 0-11 (green), to severe at 50-74 (orange), and catastrophic or code red, which is any score above 100 (black and red stripes).
The new score is called the Fire Behaviour Index. It’s also open-ended, but there are just four categories: moderate starts at a score of 12, then there’s high, extreme and catastrophic, which again represents a score above 100. Each has its own simple message of action, from “plan and prepare” to “for your survival, leave bushfire risk areas”.
The purpose of the fire danger rating system is twofold, and the first is to alert the general public to the potential risk that a bushfire poses to life and property should one ignite that day, and what actions people should take.
The ratings indicate the potential impact of a bushfire, not the actual risk of one igniting in the first place, says Heath Stimson, assistant director of community risk at the NSW Rural Fire Service.
Unfortunately, the community hasn’t always understood that distinction. As part of the rating system overhaul, fire agencies collaborated on a survey of more than 5000 Australians to find out what they knew about fire danger ratings.
This revealed that nearly three-quarters of respondents knew of the fire danger rating system without being prompted, and more than 90 per cent with prompting. But about half thought the ratings were a prediction of how likely it was for a bushfire to happen, “so if they saw an extreme or catastrophic, they’ll be like, ‘Oh, there’s definitely going to be a fire today,’ ” Stimson says.
The survey also suggested many were confused by the six levels of warning, and especially the lower levels. “They didn’t see any need to really pay attention to the sign or to the advice until the needle passed the midpoint in what we affectionately know as ‘the watermelon’,” Stimson says. “Low/moderate, high and very high – most people believe you didn’t need to do anything during that phase.” In the new system, the low/moderate classification is gone, replaced by an “off” position.
“Like a river that’s got no water in it, you don’t issue a flood warning,” Stimson says.
The ratings and signs will now be the same everywhere in Australia, to avoid potential confusion among interstate travellers or fire authorities dealing with cross-border bushfires.
The second main function of the fire danger rating system is to enable fire agencies and emergency services to plan and prepare for bushfire events, and decide when to implement measures such as total fire bans, harvest bans and closing national parks.
“If it’s going to be a TOBAN [total fire ban] or it’s going to go into extreme or catastrophic, then the level of readiness within state ops and within our districts and our brigades changes to match that,” says Corey Shackleton, a former director of community resilience at the NSW Rural Fire Service who is now with Blackash Bushfire Consulting in Sydney.
However, McArthur’s fire danger rating system was never designed to be relied on in such a fashion. His work focused entirely on fire behaviour, and in just two vegetation types – grass and forest – says Dr Miguel Cruz, a bushfire behaviour scientist at the CSIRO in Canberra.
“But fire danger is much more than fire behaviour; fire danger is about control of bushfires,” Cruz says. Fire behaviour is essentially just the physics of fire, whereas fire danger incorporates many more human elements.
When McArthur devised his scale, he classified anything above a score of 50 as extreme, “but the idea of creating that catastrophic was that it’s different from being 72, being 150,” Cruz says.
The lack of detail in vegetation types also meant the same FFDI score could indicate different things in different locations, and required some local interpretation, says Stuart Matthews , principal project officer at the NSW Rural Fire Service. “We would see that, for instance, Tasmania would issue total fire bans at FFDIs of 38, whereas in some parts of Western Australia, they’d use values of 60 or 75.”
The new system incorporates eight vegetation types, including spinifex, mallee heath and even buttongrass moorlands. It can also account for how recently an area has been burnt, which affects how a new fire might behave in that environment.
The new Fire Behaviour Index is also much more detailed in incorporating factors such as the potential for new fires to ignite, how easily they can be suppressed and the potential for fire to impact lives and property, critical infrastructure and environmental values.
“We can say that at a Fire Behaviour Index number of 15 in forest – in that range we’d expect to see fires moving at a moderate pace, there’d be short-distance spotting, flame heights of a few metres, a bit iffy for prescribed burning – shouldn’t be a problem for suppression with the usual resources you’d have locally available,” Matthews says.
With climate change contributing to longer fire seasons and more frequent intense fires, a key challenge in the overhaul was to ensure that the system is futureproof. “It’s tricky here talking about climate change, because the peak of fire danger is not getting worse – there’s a physical limitation,” Cruz says.
The new system is far more easily updated than its predecessor, allowing the many scientific models that inform it to be swapped in and out as science improves. It’s hoped that this will make forecasting far more accurate and reduce the risk of false alarms.
“The hard thing is that you get that ‘cry wolf’ issue, where people go, ‘Oh, I’ve had heaps of those kind of days, but don’t worry about it, nothing ever comes of it,’ ” Shackleton says. He says the trials of the new system showed it performed much more accurately than its predecessor. “It also got the ratings closer and when it didn’t get it right, it didn’t get it wrong by as much.”
But if the pandemic has revealed anything, it’s that we can become desensitised to warnings, even at their most extreme. Matthews says that while the redesign involved extensive social research into how people interpret and respond to fire danger warnings, it’s not clear whether the “catastrophic” setting will lose its impact if it becomes a more frequent event during bushfire season.
“If those conditions are happening more often, I don’t think we should be saying to people ‘raise the level at which you start worrying about this’,” he says. “Because if we’re saying it’s catastrophic, you really should be worried about it.”
This article was first published in the print edition of The Saturday Paper on August 27, 2022 as "Rethinking fire ratings".
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