ABSTRACT Graphical abstract of an operational framework for dry-season salinity intrusion in the Lower Mekong Delta. Salinity extent, duration, and intensity are integrated, highlighting duration as the dominant control on water usability. Key indicators (FAD, ASD, tidal risk windows) support management outcomes including adaptive allocation, intake timing, and salinity control. Dry-season salinity intrusion is a persistent operational constraint in tide-dominated deltas under reduced upstream inflows and rising sea levels. In the Lower Mekong Delta, water availability is increasingly governed by cumulative exposure to salinity rather than short-lived peak events. This study assesses dry-season salinity intrusion towards 2030 from an operational perspective by integrating salinity extent, duration, and intensity. A basin-scale one-dimensional hydrodynamic–salinity model (MIKE 11 HD–AD) was applied under three representative dry-season scenarios (P = 50%, 85%, 95%), incorporating projected upstream flow reduction and sea-level rise. Model outputs were analysed using operational thresholds of 1.0, 2.0, and 4.0 g L−1. Results indicate systematic inland expansion of salinity and increasing peak concentrations under severe conditions. However, salinity duration emerges as the dominant constraint, with large areas exposed to 4.0 g L−1 for more than 90 days, substantially limiting freshwater abstraction and irrigation feasibility. Salinity intensity governs short-term intake operability during tidal maxima, while extent defines the spatial contraction of the freshwater domain. These findings demonstrate that operational risk is controlled by the interaction of extent, duration, and intensity, supporting adaptive intake prioritisation, exposure-based irrigation planning, and time-sensitive salinity control under future dry-season conditions.
Chung et al. (Mon,) studied this question.