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An innovative warning system for extreme bushfires, designed to support firefighting services, has been developed by Adjunct Professor Rick McRae at UNSW Canberra. The system concentrates on environmental conditions that can precipitate extreme bushfires in the southeastern region of Australia.
By analysing temperature and river-flow data, it can offer early warnings months before the fire season begins, allowing authorities to determine if the upcoming season is likely to exhibit conditions conducive to extreme fires.
Extreme bushfires are unique in that they establish strong connections with the atmosphere above, as opposed to other fires that are primarily driven by surface weather conditions. With the escalating impact of climate change, the frequency of extreme bushfires is expected to rise, presenting novel challenges for fire prediction and management. While all bushfires carry the potential for destruction and pose threats to lives, extreme bushfires behave unpredictably and can give rise to phenomena such as pyrocumulonimbus, which involves the interaction between the fire and the surrounding atmosphere, resulting in violent fire thunderstorms.
It is essential to note that the new warning system, currently in a trial phase, does not serve as a replacement for the existing fire danger rating system. Instead, it is envisioned as a complementary tool to aid fire authorities in identifying times when the most severe outcomes might occur.
As Professor McRae emphasises, the unprecedented challenges posed by the “Black Summer” fires underscore the need for new tools to prepare for and combat extreme bushfires, and he hopes that this innovative predictive model can be one of those tools.
Extreme bushfires encompass a range of characteristics, including “deep flaming,” where active burning occurs simultaneously across an extensive fire front. Unlike a typical bushfire, which might have a fire front tens of metres in depth, an extreme bushfire can cover hundreds of meters, or even kilometres, due to spot fires igniting over a vast area. Fires driven by the foehn effect, wherein hot and dry winds from higher terrain exacerbate the fire, were once rare but accounted for about half of the major events during the Black Summer. Furthermore, the incidence of fire thunderstorms has increased significantly in the past two decades.
To evaluate the conditions under which extreme bushfires could ignite, Professor McRae developed the Hierarchical Predictive Framework. This framework incorporates the latest research and practical knowledge on extreme bushfires and combines decades of operational experience in battling bushfires in the ACT with groundbreaking scientific advancements made by UNSW Canberra since the 2003 bushfires.
The model relies on four tiers of data to inform its predictions, including an assessment of temperature anomalies and river flow levels. The city of Canberra, chosen for its suitability, records temperature data. The “Canberra Dipole” is created by comparing the average temperature over the 12 months leading up to the bushfire season with data from the Bureau of Meteorology. Elevated values of the Canberra Dipole suggest the potential for synoptic weather patterns to generate trough systems in southeast Australia, exacerbating extreme fires.
Additionally, the model considers river flows from 17 locations across south-east Australia. While there are various methods to gauge the flammability of smaller fuel sources, such as twigs and fallen leaves, assessing soil dryness using river levels provides a more accurate picture of the flammability of larger fuels like logs.
To assess the model’s effectiveness, Professor McRae applied it retrospectively to more than 20 years of data from previous bushfires. The results were promising, demonstrating a high level of accuracy in predicting extreme bushfires during periods when specific temperature and river conditions were met.
Looking ahead, the model will be put to the test in upcoming fire seasons to further refine its accuracy. As it stands, this innovative warning system appears poised to become a highly effective tool to assist fire authorities during challenging fire seasons, ultimately enhancing the preparedness and response to extreme bushfires in south-eastern Australia.
