Characterization of the climate-change-induced major floods on the southeast Australian coast

Coastal areas are influenced by both oceanic and catchment forcings and are particularly vulnerable to climate change impacts. More frequent and severe floods are expected on the southeast Australian coast under the changing climate. This study applied a hydrodynamic model, RMA-2, with a one-dimensional mesh, to investigate inundation depths and area during the climate-change-induced major floods in the Georges River Estuary, Sydney, Australia. Forced by the 20 year ARI historical and high emission future scenario flood conditions, RMA-2 predicts the future peak water levels will rise approximately 0.8 – 1.3 m in the upper estuary and the total inundation area will expand 60% in the absence of changes in oceanic forcing. The Intergovernmental Panel on Climate Chang (IPCC) sixth report projected sea level in the eastern Australia would rise by an average of 0.66 m by 2090 under a high emission scenario. When combined with a predicted 20 year ARI barometric rise of 0.26 m sea level rise, future flood peak water level are predicted to rise 1.4 m in the upper estuary and 0.9 m in the lower estuary at 20 year ARI. Consequently, under climate change, catchment floods dominate changes in peak water level in the upper estuary while oceanic processes principally determine changes in the lower estuary. Climate changing storm wind effects are negligible on extreme water levels. Climate change storm impacts are predicted to have significant impacts on inundation of densely-populated regions, especially on Australian east coast.