Salinity intrusion dynamics in the Vietnamese Mekong Delta: Combined effects of upstream development, climate change, and coastal engineering

Study region Vietnamese Mekong Delta (VMD) in Southern Vietnam Study focus This study assesses and predicts spatial and temporal salinity intrusion dynamics under changing inflows, climate scenarios, and sea-level rise. Using the MIKE 11 hydrodynamic model, calibrated with 2016–2020 salinity data, dry-season (February–May) intrusion was simulated across nine scenarios: a historical 1998 baseline (SCE1), 2020 present conditions (SCE2), projected sea-level rise (SCE3) under RCP4.5 and RCP8.5 (SCE4–5), and a future combined upstream-development package that integrates full hydropower operations with moderate or high irrigation expansion (SCE6–9). Three additional scenarios (SCE7-G1–G3) tested the effects of salinity-regulating sluice gates. New hydrological insights for the region Compared to the historical baseline SCE1 and the present-day scenario SCE2, projected scenarios exhibit higher salinity, stronger penetration, and earlier arrival times due to upstream alterations. The most severe regional degradation occurs when climate-driven sea-level rise directly coincides with intensive upstream water diversions, with the combined drivers under RCP4.5 paradoxically generating a larger area enclosed by the 2 PSU interpolated river-salinity surface than the higher-emission RCP8.5 due to lower projected dry-season inflows. Furthermore, the simulations expose an important hydrodynamic trade-off in coastal engineering, while localized sluice gates successfully mitigate salinity on a local scale, restricting these natural channels alters tidal distribution and can inadvertently intensify saltwater encroachment in adjacent, unfiltered river branches.