Assessing flood hazard changes using climate model forcing

Abstract. A modelling framework for using regional climate projections to assess flooding hazard has been developed and applied to the Gwydir River (catchment 26 600 km2 and floodplain 8100 km2), NSW, Australia. The model framework uses NSW and ACT Regional Climate Modelling version 1.5 projections combined with computationally efficient hydrologic and hydraulic models. Although it required model management and high-performance computing resources, the modelling framework successfully processed 18 regional climate projections into flood projections. Specifically, a six-member set of climate model combinations simulating a historical period (1951–2005) and a future period (2006–2100) under two global emission pathways (RCP4.5 and RP8.5) were used to predict flood depth and speed. In total, 1470 continuous years were simulated at hourly time steps. These flood (depth and speed) projections were analysed to assess the flood hazard changes under future climate scenarios by estimating changes in the annual probability of occurrence of a range of flood hazard classes. The six-member ensemble indicates that the flood hazard in the Gwydir Valley will decrease in the short, medium and long term. There are also cases within the ensemble, which includes increases in all non-safe flood hazard classifications while decreasing the safe flood hazard classification.