Sinking city : The future of Bangkok amid Climate Change and Rising Sea Level

Bangkok and its metropolitan area (BMA) are highly vulnerable to compound flood hazards arising from both fluvial and coastal processes. This study investigates regional-scale compound flood impacts using a two-dimensional hydrodynamic model (Flo-2D) that integrates future climate projections from General Circulation Models (GCMs) under CMIP6 emission scenarios. Precipitation and river discharge were statistically downscaled and bias-corrected using the Robust Empirical Quantile Mapping (RQUANT) method. A Neuro-Genetic Algorithm (NGA) model was subsequently used to forecast river discharge, combining the adaptive learning capability of neural networks with the global optimization power of genetic algorithms. Results show that six-month monsoon precipitation is projected to increase by 3.92% (8.16%) and 12.72% (21.47%) under SSP2-4.5 (SSP5-8.5) by 2050 and 2100, respectively. Relative sea level rise further intensifies coastal flooding, with inundation areas projected to expand by 3.2% (3.6%), 8.2% (8.4%), 14% (15.1%), and 21.4% (26.2%) in 2030, 2050, 2070, and 2090, respectively. The findings highlight the inadequacy of the current national master plan in addressing compound flood risks. The interaction of intensified fluvial flooding and rising sea levels will amplify the severity and extent of future flood events. Strengthening adaptive urban planning, integrated water management, and early warning systems is essential to enhance Bangkok’s resilience under future climate conditions.