Assessing extreme flood inundation and demographic exposure in climate change using large ensemble climate simulation data in the Lower Chao Phraya River Basin of Thailand

Study region: Lower Chao Phraya River Basin (LCPRB), Thailand.Study focus: This study aims to make a robust assessment based on a large ensemble d4PDF dataset and a flood-inundation model Inundation Model Coupling Rainfall-runoff (IMCR) for the LCPRB. Inundation area and depth for 100-year flooding are evaluated for the flood volume of capacity greater than 2000 m3/s for both past (1951-2010) and future (2051-2100) climates. This study also evaluates the affected population exposure in the region for both past and future climate scenarios.New hydrological insights for the region: The IMCR inundation simulation findings indicate that compared to the historical climate, the inundation area increases by an average of 1.0-1.4 times, and the critical area (depth >3 m) increases by an average of 1.1-1.3 times. On the other hand, the exposed population in the future, with respect to the SSP5 scenario "Taking the Highway," is expected to decrease on average by 0.7-0.9 times in comparison to the past climate for depth > 0 m. However, keeping the population constant as in the past, the exposed population is likely to increase on average by 1.3-1.4 times in comparison to the past climate for depth > 0 m.