Assessing future flood hazards in the major rivers of Bangladesh using CMIP6 projections and integrated hydrologic-hydraulic modeling

Climate change is expected to significantly alter flood dynamics in Bangladesh, one of the world's most flood-prone countries. Yet quantitative assessments of future flood hazards in this region remain sparse. This study pioneers an integrated approach to project future flood characteristics in Bangladesh's major rivers - Ganges, Jamuna, and Padma - for the period 2051-2070 under the SSP2-4.5 and SSP5-8.5 scenarios. We uniquely combine bias-corrected climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) with hydrological modeling using the Hydrologic Engineering Center's Hydrologic Modeling System and River Analysis System, providing a comprehensive assessment of flood hazard evolution. Our analysis, based on data from the Bangladesh Water Development Board (BWDB) and multiple Global Climate Models (GCMs), includes rainfall-runoff simulations, model calibration, flood frequency analysis, and one-dimensional steady-flow simulations. Results show projected increases in peak discharges of 6%, 10%, and 5% for the Ganges, Jamuna, and Padma rivers, respectively, compared to the baseline from 1996 to 2022. The Ganges shows the highest potential increase, up to 26.51% for the 100-year return period discharge, with the water level rising up to 0.71 meters. Despite the highest increased discharge projections, the Jamuna exhibits unexpected decreases in projected water levels for design flood discharges of greater return periods compared to the baseline. The Padma shows moderate increases in extreme flood risk. These river-specific responses underscore the complexity of climate-driven hydrologic change and highlight the importance of integrated modeling approaches in guiding adaptive flood risk management and climate resilience planning in deltaic environments.