CFA fire behaviour analysts have identified a gap in Australia’s landscape dryness indicators and are presenting an alternative that could lead to better bushfire preparedness.
Fire behaviour analysts are increasingly finding previously used measures, such as the Keetch-Byram Drought Index (KBDI) and Drought Factor (DF), used for the last 60 years, are not providing the nuance in the dryness of forest fuels across south-east Australia to determine bushfire potential.
CFA Predictive Services Specialist Andy Ackland saw an opportunity to investigate the potential to use gridded soil moisture as a more accurate alternative, similar to work done in the United States.
“In recent years, there have been vast improvements in research and data sources in relation to landscape water balance and soil moisture, with national grids of soil moisture now published daily and historically by the Australian Bureau of Meteorology (BOM),” Andy said.
“We know drought is bad for bushfires and BOM soil moisture products helped us flag heightened risks ahead of the 2019-20 bushfire season, but a key science gap is understanding when and how forests dry out and transition to a condition that can support bushfires.
“To start off, I extracted every fire since 1972 in Victoria up until 2024 and retrieved the corresponding soil moisture values for every one of those 37,000 fires and their vegetation classes. This revealed fascinating patterns of fire occurrence in relation to soil moisture.
“I discovered that there is quite a sharp threshold once you’re getting below 40 percent root zone soil moisture and below 4 percent in upper soil moisture. That’s where fires suddenly started to appear.
“When values were much higher than this, there was generally low occurrence of bushfires, even if bushfire weather conditions were elevated.
For the last two years, Andy has been developing a protype of a new Fuel Availability Factor (FAF) that represents a scale of landscape dryness from 0 (wettest) to 10 (driest) and said it has the potential to be of immense value to fire preparedness planning.
“CFA is a national leader in this space, with a dedicated research and development team who has been able to innovate not just in this area but also in other topics such as suppression effectiveness, firefighting aircraft drop-testing, and bushfire reconstructions,” Andy said.
“Having worked in fire behaviour analysis in Australia as well as in British Columbia, Canada; my relationships with national and international counterparts has helped me to drive this further.
“Quite a few of my colleagues in other jurisdictions are eagerly wanting to try this new alternative.
Andy and his counterparts are tasked with informing significant decisions about evacuations, community warnings, control strategies, suppression efforts and potential impact to infrastructure.
During last summer’s major bushfires, Andy worked in a strategic planning unit in the State Control Centre where he was asked by fire Chiefs for a strategic outlook, analysing potential for the fires to spread further and impact more communities.
“An important question during January was whether the fires in Great Otway National Park could get right through to Lorne and the Great Ocean Road which could have been devastating,” Andy said.
“Our old crude drought indices were again proving to be inaccurate, so I utilised my new landscape dryness model.
“Elevated soil moisture in the tall wet forests meant they were still too damp to burn, and this was validated on the ground; it meant there was a critical strategic buffer to control the fires and keep them away from the Great Ocean Road, but it might only last a few more weeks (at that time).
“We also advised there was a threat to Gellibrand because it was much drier, and the drought-affected forests and the climate patterns of the southwesterly wind change was suggesting they were the most in line of impact. We indicated this in the potential mapping very early on.
While further evaluation of the new FAF model is required before it can become operational, Andy continues to work with colleagues in CFA, Forest Fire Management Victoria (FFMVic) and NSW Rural Fire Services (RFS) to trial this new innovation in the Australian Fire Danger Rating System (AFDRS).
Andy will be speaking at the AFAC Conference in Melbourne on 18 August 2026, alongside colleagues Dr Sarah Harris, Rachel Bessel, Kristy Butler, Nick McCarthy, Brigid Ennis, Georgina Hill, Liv Duffey and Tanya Lumley.
