Causes of Big Bushfires in Australia: Higher Temperatures and Rainfall or More Fuel?

Abstract

The 2019-2020 bushfires in Australia caused the loss of 34 lives and an estimated 100 bn AU$ damage. This has sharpened the apparent division between Australians who believe that the increasing number of bushfires is due to climate change, and those who suggest that fuel loads must be managed more carefully. Bushfires whose area equals or exceeds 1 mHa have been analysed in this paper. The results show that the number, duration, and size have increased over the period 1850-2020, but that since 1953, there has been a downward trend in the number of big bushfires. There is a range of temperatures of about 20˚C that are associated with the fires, with a modal temperature of 30˚C -32.5˚C. Using an analysis of the maximum temperatures for the period 1970-2020 as a standard for comparison with bushfires for the period 1850-2020, shows that during bushfire events the standardised temperatures have a downward trend. This is most clearly shown by the application of the Fisher Exact Test. This suggests that the fuel load in forests is a key factor for bushfires. The role of pre-bushfire rainfall shows a rapid rise in the area burnt when the rainfall exceeds 150 mm month −1 which would lead to more plant growth and hence fuel load. The role of traditional burning over the whole of Australia is described based on documentary evidence. A tentative cost benefit analysis has shown that a comprehensive program of wildfire management is cost effective. The recommendations of previous research, National Inquiries and more recent management practices, have all failed to prevent the 2019-20 fire disaster in Australia.

A climatology of aerosol optical depths in the ultraviolet wavelengths for Hobart, Australia, as determined by a Brewer MKIII spectrophotometer

“…By contrast, the 95 percentile values show high variability throughout the year with a maximum in January of 0.39 and decreasing to 0.16 in July. This pattern is typical of an environment with low aerosol load but with occasional intrusions of heavily contaminated air masses mostly related to bushfire events (Clark, 2020).…”

“…Despite the large standard deviations, the slope statistic shows an increasing trend with a probability less than 1% that it occurred by chance. The continuous pattern is likely a result of the increasing incidence of large bushfires in the Australian region, including their size and duration (Clark, 2020), which is partly a result of increasing fire‐prone weather events (Fox‐Hughes et al ., 2014; Dowdy, 2018). Figure 9a shows yearly precipitation from 2002 to 2019 plotted as anomalies from their 30‐year means (1991–2020).…”

Rainfall-Linked Megafires as Innate Fire Regime Elements in Arid Australian Spinifex (Triodia spp.) Grasslands

“…A highly referenced series of pre-contact Aboriginal fire scars from the Western Desert are those captured by the 1953 Blue Streak and 1960/1961 aerial photography (Burrows and Chapman, 2018;Clark, 2020). These fire observations have been held as strong evidence that the pre-contact fire FIGURE 5 | Large-scale short-interval wildfires in west central Australia in the early 1980s.…”

Variability analysis of monthly precipitation vector time series in Australia by a new spatiotemporal entropy statistic

“…For example, regions with high risk of seasonal bushfires often have the majority of their annual precipitation proportions in winter/wet months [29]. An increased proportion of this annual precipitation occurring in winter significantly increases the risk of fire [30]. Early adaptation to changing intra-annual precipitation concentration allows for better mitigation of such extreme precipitation hazards.…”