The frequency of major flooding in coastal southeast Australia has significantly increased since the late 19th century
Australian Meteorological and Oceanographic Journal
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
... 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. Power. Frequency of major flooding in coastal southeast Australia 3 The database containing the flood records took many years to construct. Callaghan and Power (2014) used both instrumental and historical data, including newspapers, for the period 1860-2012. Their study region, which we adopt, extends from Brisbane (the largest city in Queensland) in the north, through Sydney (the largest city in Australia), to Eden (New South Wales; NSW) to the south (Figure 1 ). Callaghan and Power (2014) considered a flood to be 'major' in two broad cases: (1) the inundation of a river within approximately 50 km of the coast. A river is regarded as 'inundated' if it causes extensive flooding in rural and/or urban areas. 'Extensive' flooding is characterised by the flooding of buildings above floor level, the isolation of properties and towns, and/or the closure of major rail and traffic routes; (2) non-riverine flooding inundates similar areas overland near the coast from the active part of a weather system, and extends at least 20 km along the coast. If major flooding occurred under (1) or (2) in more than one catchment, it is regarded as a single major flood.