Impact of ENSO on coastal flood risk from extreme rainfall and storm surge

: Coastal flood risk is affected by multiple processes, including extreme rainfall and storm surge, leading to compound flood events with higher risk than those caused by a single mechanism. There is strong evidence that these compound floods are related to meteorological forcing, such as large pressure or wind systems, and climate phenomena, such as the El Niño Southern Oscillation (ENSO). Therefore, understanding how these climate phenomena affect the dependence between the drivers of these compound flood events is an important step towards the understanding of future coastal flood risk, especially when the occurrence of extreme climate phenomena, such as ENSO events, is projected to become more frequent under climate change. In this study, we examined the impact of one of the most important climate phenomena - ENSO on dependence between storm surge and rainfall in Australia using both observed and modelled data and found dependence is contributed by unequally-weighted mechanisms. Although La Niña drives the dependence along the majority of the Australian coastline, there can be increased dependence between extreme rainfall and storm surge during El Niño in some locations. The varying impact of ENSO can be due to interactions between climate phenomena and local features, demonstrating need for greater understanding of composition of compound flood risk. Our results also show that it is possible to use integrated process-driven models to establish a better understanding of whether extreme rainfall and storm surge are more likely to co-occur under climate change and exacerbate future compound risk.