Assessment of future flash flood inundations in coastal regions under climate change scenarios@@@A case study of Hadahe River basin in northeastern China

Highlights: @@@ Coastal regions in China are exposed to extreme flash floods induced by TCs. @@@ Integration of GCMs and hydrodynamic model can assess severity of future hazard. @@@ Significant underestimation of extreme precipitation exists in GCMs. @@@ Poor simulation of TCs is the main reason for underestimation in Hadahe River basin. @@@ Climate change is likely to increase risk of flash floods in Hadahe River basin. -- Abstract: Climate change may considerably influence flash floods by increasing extreme precipitation. Coastal regions in eastern and southern China may experience especially negative effects because of the frequent occurrence of tropical cyclones (TCs). This study presented a hazard assessment framework for TCs-induced flash floods under climate change scenarios and assessed future inundations in Hadahe River basin, which is in northeastern China. From 1965 to 2014, there were twenty-four TCs ranging from severe tropical storm to super typhoon over Hadahe River basin in twenty years. General Circulation Models (GCMs) are too coarse to depict the impact of TCs on extreme precipitation; therefore, hourly precipitation data from two gauges and the tracks of TCs were used to assess the impact of TCs. An extreme precipitation event on 3@@@4 August 2012 and the same 600-year future probabilistic extreme rainfall were utilized to investigate the impact of climate change. Daily precipitation data from eight climate models from the NEX-GDDP dataset during 1965@@@2005 and 2050@@@2099 represented historical and future simulation conditions, respectively. The hydrologic model HEC-HMS was integrated with the hydraulic model FLO-2D to simulate discharges and inundations of past and future TCs episodes. The results showed that flooded area is projected to increase by 6.6% and 7.8% for inundation depth between 1.0 and 3.0 m under RCP 4.5 and RCP 8.5 scenarios, respectively. For inundation depth over 3.0 m, flooded area is projected to increase by 17.6% and 22.0%. Relative change of flash flood extent increases as inundation depth increases, indicating that climate change is likely to increase the risk of flash floods. Additional adaptation measures are needed to make the Hadahe River basin and other similar coastal basins more resilient. The results also indicated that considering the impact of TCs produces a more reliable assessment of future flash floods in coastal regions.