Impacts of tropical cyclone induced storm surges on water resources in coastal Bangladesh and implications for population health

Major land reclamation using polders took place along the southern coastal area of Bangladesh during the mid‑20th century. These polders, located in the Ganges–Brahmaputra–Meghna Delta, are protected by earth embankments approximately 2 metres high. While the embankments restrict tidal ingress of saline water, they can be breached or overtopped by storm surges produced by tropical cyclones in the Bay of Bengal. These surges, in turn, cause large volumes of saline water to enter and remain trapped within the polders, adversely affecting both shallow groundwater and surface water sources. Many communities continue to rely on these sources for drinking water despite sodium concentrations exceeding 200 mgNa/L. Epidemiological studies have linked long‑term exposure to such levels with adverse cardiovascular, renal, and pregnancy‑related health outcomes. Enhanced ocean warming due to climate change is expected to result in more frequent and intense tropical cyclones and associated storm surges. Consequently, there is a need for improved understanding of the impacts of, and recovery from, such storm‑surge events to support long‑term adaptation and improved health outcomes. This, however, is challenging due to the combined and interacting nature of surface‑water and groundwater processes.

To address these challenges, the hydrodynamic and salinity responses of a low‑lying coastal aquifer in Dacope, southwestern Bangladesh, were investigated using two‑dimensional (2D) and three‑dimensional (3D) numerical models developed in HydroGeoSphere. Field observations and hydrogeological data were integrated to simulate surface‑water and groundwater responses under ambient and storm‑surge conditions. The 3D simulations revealed interacting mechanisms controlling both the persistence and spatial heterogeneity of storm‑surge‑induced salinization. Comparison with 2D simulations showed that omitting lateral storage and cross‑sectional flow leads to rapid surface drainage and systematic underestimation of near‑surface salt accumulation and recovery timescales. The results provide important insights into the long‑term impacts of storm‑surge inundation, the identification of salinity‑vulnerable zones, and contribute to a large‑scale joint UK–Bangladesh project on multi‑sectoral interventions aimed at improving access to low‑salinity drinking water for health protection in the coastal areas of Bangladesh.