The frequency of major flooding in coastal southeast Australia has significantly increased since the late 19th century

Millions of Australians live in a 1500 km stretch of coastal catchments in southeast Australia. Major flooding in this region causes death, economic loss and major disruptions to the lives of its inhabitants. Concerns have been raised that anthropogenic climate change might lead, or has already led, to an increased risk of extreme rainfall and associated flooding. Images of flooding commonly appear in the media, fuelling perceptions that flood frequency has already increased. Here we use a new dataset that allows us to estimate reliable trends over much longer periods than has previously been the case. The statistical significance of the trends is assessed using a method that is suitable for the non-Gaussian, serially correlated flood frequency data. We identify a statistically significant, increasing trend in the frequency of major floods since the late 19th century, which contributes to a 50% increase in frequency. While possible reasons for the increase are discussed (e.g. land use change, anthropogenic climate change, natural climate variability), further research is needed to clarify the relative importance of possible contributors.