The potential of using magnetic susceptibility to identify past wildfires in Australia

Fully understanding the causes and frequency of wildfires has never been more important than it is today, with potentially thousands of lives at risk from wildfire smoke in Australia alone. Until now wildfire frequency in Australia has been estimated based solely on observed fire events, records that barely cover the last century. This coverage is severely inadequate for a reliable estimation of wildfire frequency. Here, it is suggested that records of magnetic susceptibility may help extend the wildfire records used, which will significantly increase the confidence level of estimated wildfire frequency. With Australian soils being rich in iron, the main factor limiting the use of magnetic susceptibility appears to be rainfall. Additionally, the magnetic susceptibility records of several sites may respond more to local hydrology or organic matter content than to wildfires, possibly owing to insufficient heating of the soil. A comprehensive field study is thereby suggested, which will determine which site characteristics have the most significant influence on magnetic susceptibility records in Australia. This will enable more detailed studies to be conducted and will extend Australia’s fire records.