El Nino-Southern Oscillation: Related probabilities of fatalities from natural perils in Australia

The interannual variability of flood, bushfire and heatwave fatality data f or eastern Australia during the period 1876-1991 was analysed with respect to the phase of the El Nino-Southern Oscillation (ENSO) and the associated values of the Southern Oscillation Index (SOI). Heatwaves were found to be the most serious peril in terms of the total number of fatalities, while fl oods ranked first in the fatality event day statistics. None of the three m onthly (absolute value) fatality data sets showed significant correlations with the corresponding values of the SOI, while the correlation analysis of annual (July to June) data led to significant correlation coefficients of 0.5 for floods and -0.3 for bushfires. Additional SOI value-related classif ication of the standardised fatality event days into several ENSO categorie s confirmed the correlation trends by showing an increase (decrease) in the standardised bushfire (flood) fatality event day frequencies with increasi ng values of the SOI. In contrast to that, the standardised heatwave fatali ty data showed an inconclusive distribution pattern, which hints at the inf luence of other possible factors (such as air pollution) on heatwave-relate d fatality numbers. The results of a risk assessment analysis have shown that the probability o f reaching the mean annual number of flood-fatality event days is roughly f our times higher during La Nina seasons (80%) than the corresponding probab ility associated with El Nino periods (18%). The corresponding probabilitie s associated with the mean bushfire and heatwave fatality event days displa yed a reversed pattern, with the probabilities of El Nino-related years bei ng roughly twice as high as those associated with La Nina seasons (70% and 30% for bushfires, and 60% and 25% for heatwaves, respectively). Further pr obability calculations performed on the totals of fatalities from all three perils identified the La Nina years as potentially the most dangerous in t erms of suffering fatalities from these perils. Furthermore, they highlight ed the significant differences between the means of fatality event day numb ers recorded during years of extreme SOI values (9.8 for La Nina, and 9.1 f or El Nino seasons) and those marked by near-zero SOI values (6.6). The maj or reason for the increase in risk associated with extreme ENSO phases was the higher variability of these perils during the respective seasons.