Unusual weather during Black Saturday bushfires
New research identifying unique weather patterns that affected fire behaviour on Black Saturday could inform future fire management and warning systems.
New research identifying unique weather patterns that affected fire behaviour on Black Saturday could inform future fire management and warning systems.
The first of its kind to produce detailed, high-resolution simulations of weather patterns on black Saturday, a Melbourne University led study revealed that the extremely hot, dry and windy conditions on the day combined with structures in the atmosphere called 'horizontal convective rolls' -similar to streamers of wind flowing through the air were likely to have affected fire behaviour.
Chair of Meteorology at Monash University, Professor Michael Reeder worked closely with Melbourne University researchers and the ARC Centre of Excellence for Climate System Science, to examine meteorological conditions across Victoria on 7 February 2009.
Professor Reeder said a strong late-afternoon cool change and a second weaker late-evening cool change on the day altered conditions dramatically as it moved across the state.
“Daytime temperatures exceeding 45 degrees celcius, strong surface winds, and extremely dry conditions combined to produce the worst fire weather conditions we’ve ever seen and recorded,” Professor Reeder said.
“The meteorology of the day was simulated at very high resolution, which enabled us to examine in detail the wind and temperature structures that effected fire behaviour.
Professor Reeder said one of the most remarkable results from the study was that after sunset the cold front generated a wave (technically called an undular bore).
“The passage of this wave appears to have been responsible for the reinvigoration of the Beechworth fire. Although we believe that this kind of behaviour is common, this is the first time it has been documented,” Professor Reeder said.
Researchers found weather events at a horizontal scale of about 10 kilometres introduced variability in the wind, temperature and humidity conditions. These smaller events combined to produce significant variability in fire danger across much of Victoria.
The analysis used a high-resolution weather forecasting model, which represented the airflow over the entire state on 400 metre weather grids, which are about ten times smaller than the grids used in operational weather forecasting. Weather conditions observed on the day were used to validate the model.
The researchers said with improved computing power in the future, this kind of analysis could be useful for operational forecasting on days of fire danger, providing a better guide for public warning systems and fire fighting resources.
The study was funded by the Australian Research Council and is published online in the Quarterly Journal of the Royal Meteorological Society.