Studies: No Trend In ‘Compound’ Natural Disasters Across Australia Since 1966
Three new studies affirm there has been no significant change in natural disasters, precipitation, or bushfire across Australia for the last several decades.
Instances when perilous flooding, droughts, bushfires, cyclones, storms, heatwaves…occur at the nearly same time are classified as “compound disaster” events.
Across Australia, there has been no statistically significant trend in compound disaster events over any period in the last 50 years.
The predominant and most predictable driver of climate-related disaster events is not anthropogenic global warming, or CO2 emissions, but the El Nino Southern Oscillation.
“Here we utilise an Australian natural disaster database of normalised insurance losses to show compound disasters are responsible for the highest seasonal financial losses. Though their component events occur most frequently in the eastern seaboard, they may also comprise disasters on both sides of the continent. There has been no temporal trend in their frequency since 1966. A new compound disaster scale is proposed for Australian conditions. A bootstrapping analysis reveals the pairing of Bushfire and Tropical Cyclone to occur far less often than would be expected by chance. This is because these perils occur most frequently under contrasting climate states. Climate variability influences the frequency, intensity and type of perils contributing to compound disasters with the clearest relationship being with the El Niño Southern Oscillation. Given that ENSO is the most predictable climate driver at seasonal timescales, this may assist better forecasting of their occurrence and higher degrees of readiness.”
Image Source: Gissing et al., 2021
Precipitation patterns across Australia also show no detectable trend in the last 50 years, as some regions have experienced more rainfall and some less rainfall.
As a whole, however, the country has become slightly wetter since 1960 (as indicated by the larger concentrations of blue in the below images).
“Northern parts of Australia have experienced increasing annual rainfall totals, resulting in increased water availability in the tropics with increased soil moisture, evapotranspiration, and runoff, particularly during the hot, wet monsoon season. In contrast, the southwest and southeast coast of Australia have experienced declines in rainfall, particularly in the colder months, corresponding with decreasing evapotranspiration, soil moisture, and runoff. Trends in flooding are aligned with runoff trends, and closely follow trends in rainfall, with changes in soil moisture of secondary influence. Streamflow droughts, measured by the standardised runoff index, are increasing across large parts of Australia, with these increases more widespread than changes in rainfall alone. Increases in rainfall in the tropics of northern Australia appear to be related to decreasing drought occurrence and extent, but this trend is not universal, suggesting changes in rainfall alone are not an indicator of changing drought conditions.”
Another new study indicates Australia is far less prone to fire today than it was 4,600 to 2,800 years ago. All proxies denoting fire incidence have shown a significant decline in the last 900 years.
“Fire has a long history in Australia and is a key driver of vegetation dynamics in the tropical savanna ecosystems that cover one-quarter of the country. Fire reconstructions are required to understand ecosystem dynamics over the long term but these data are lacking for the extensive savannas of northern Australia. This paper presents a multiproxy palaeo fire record for Marura sinkhole in eastern Arnhem Land, Northern Territory, Australia. The record is constructed by combining optical methods (counts and morphology of macroscopic and microscopic charcoal particles) and chemical methods (quantification of abundance and stable isotope composition of pyrogenic carbon by hydrogen pyrolysis). This novel combination of measurements enables the generation of a record of relative fire intensity to investigate the interplay between natural and anthropogenic influences. The Marura palaeo fire record comprises three main phases: 4600–2800 cal BP, 2800–900 cal BP and 900 cal BP to present. Highest fire incidence occurs at ~4600–4000 cal BP, coinciding with regional records of high effective precipitation, and all fire proxies decline from that time to the present. 2800–900 cal BP is characterised by variable fire intensities and aligns with archaeological evidence of occupation at nearby Blue Mud Bay. All fire proxies decline significantly after 900 cal BP. The combination of charcoal and pyrogenic carbon measures is a promising proxy for relative fire intensity in sedimentary records and a useful tool for investigating potential anthropogenic fire regimes.”
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