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A 91���˰涶��researcher has developed a world-first warning system for extreme bushfires to assist firefighting services.

The new warning system, developed by Adjunct Professor Rick McRae, specifically looks at the environmental conditions that can lead to extreme bushfires in south-east Australia. It can provide a warning months before a fire season by examining temperature and river-flow data and determining if the coming season is likely to exhibit conditions conducive to extreme fires.

Extreme fires are ones that forge strong links with the atmosphere above, whereas other fires are driven by surface weather.

Prof. McRae has written an in the Australian Journal of Emergency Management explaining the framework that underpins the warning system.

Increasing severity of bushfires

With the increasing influence of climate change, extreme bushfires are expected to be more frequent and present new challenges for fire prediction and management.

While all bushfires have the potential to be destructive and pose a risk to lives, extreme bushfires differ from others as they often behave unpredictably and can lead to phenomena such as pyrocumulonimbus – in which the fire interacts with the surrounding atmosphere to create violent fire thunderstorms.

Prof. McRae emphasised that the new warning system, which is still in a trial phase, was not a replacement for the current fire danger rating system, but that it should be viewed as a complementary tool to assist fire authorities identify times when the worst outcomes might eventuate.

“What we saw during the Black Summer fires suggests the bushfire rule book has been completely rewritten,” Prof. McRae said.

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“We saw a dramatic increase in the number of extreme wildfires, including fire types that had previously been rare.

“Black Summer made it clear we need new tools to help prepare for and fight against these extreme bushfires, and I hope this new predictive model can be one of those.”

Extreme bushfires include those that demonstrate ‘deep flaming’, where there is active burning simultaneously across a large fire front. The fire front of a ‘normal’ bushfire might be tens of metres in depth, whereas an extreme bushfire might cover hundreds of metres, or even kilometres, due to spot fires igniting over a large area.

Fires driven by the foehn effect, in which hot and dry winds from higher terrain exacerbate the fire, were once rare, but they accounted for about half of the major events during the Black Summer. Between 1980 and 2003 there were fewer than 10 fire thunderstorms recorded, in the following 20 years there have been more than 120 of these events.

Bushfire risk in south-east Australia

To assess the conditions under which an extreme bushfire could ignite, Prof. McRae developed the Hierarchical Predictive Framework which uses the latest research and practical knowledge on extreme bushfires to assess the likelihood of occurrence. It combines his decades of operational experience with bushfires in the ACT with the ground-breaking science that has been conducted by 91���˰涶��since the 2003 bushfires.

The model uses four levels of data to inform the prediction, including an assessment of temperature anomalies and river-flow levels.

Canberra was determined to be a useful location to record temperature. The average temperature across the 12 months leading up to bushfire season is compared with Bureau of Meteorology data to create the ‘Canberra Dipole’.

When the Canberra Dipole is elevated, there is the potential for synoptic weather patterns to produce trough systems in south-east Australia that exacerbate extreme fires.

The model also takes into account river flows from 17 locations across south-east Australia. While there are several ways to determine the flammability of smaller fuel sources, for example twigs and fallen leaves, determining soil dryness using river levels paints a clearer picture of the flammability of large fuels like logs.

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Prof. McRae applied the model retrospectively to more than 20 years of data from previous bushfires to determine its effectiveness.

“I was able to demonstrate with a high level of accuracy that periods when these temperature and river conditions were met have previously aligned with extreme bushfires in south-east Australia,” Prof. McRae said.

“The next step is to use the model in the coming fire seasons to further assess its accuracy and refine the model.

“But as things currently stand the model looks like it can be a highly effective warning system to assist fire authorities during bad fire seasons.”

Read more about Prof. McRae’s observations and collected data and other new being developed by 91���˰涶��researchers.