Contribution of tropical cyclones to extreme rainfall in Australia

Abstract

The contribution by tropical cyclones (TCs) to extreme rainfall in Australia is examined using daily rainfall measurements from over 2000 rain gauges. Analyses focus on the period beginning with regular satellite monitoring of TCs (1969/1970) through the year 2012/2013 and consider daily and multi-daily annual maximum rainfall series. Our results indicate that TCs play a prominent role in extreme rainfall over much Australia, with more than half of the highest annual rainfall events associated with these storms over the coastal regions and in particular over Western Australia. Moreover, the TC fractional contribution to extreme rainfall increases as we focus on the largest rainfall events, with approximately 66-100% of annual maxima in excess of 100mm (∼4inches) over Western Australia associated with TCs at over one third of the locations. Given the well-established controls on Australian TC activity by the El Niño-Southern Oscillation (ENSO), we also examined the relationship between extreme rainfall associated with TCs and ENSO using logistic regression. A larger probability of having an annual rainfall maximum related to TCs occurs during La Niña years, consistent with enhanced Australian cyclogenesis during these phases of ENSO. We also highlighted regional differences in the link between ENSO and extreme rainfall events, highlighting the stronger connection along the coastal areas and in particular over Western Australia.