Sea level rise

Sea level rise represents a fundamental background forcing shaping hydrodynamic and geomorphological processes along the Mekong Delta coast. Given the delta’s extremely low elevation—typically on the order of 0.5–1.5 m above mean sea level—the system is inherently sensitive to even modest increases in sea level. Available observations indicate a regional sea level rise rate of approximately 4 mm/year, with evidence of acceleration in the post-2015 period, consistent with broader global trends.

An increase in mean sea level effectively raises the hydraulic baseline of the deltaic system, altering tidal propagation and inland water level dynamics. Under these conditions, tidal signals penetrate further upstream, particularly during the dry season when fluvial discharge is limited, enhancing salinity intrusion and increasing the spatial extent and duration of coastal inundation. In addition, elevated mean water levels increase the likelihood and magnitude of extreme water level events, placing additional stress on coastal defenses and low-lying infrastructure.

From a coastal processes perspective, deeper nearshore water reduces wave energy dissipation across the shallow shelf, allowing waves to reach the shoreline with greater energy. This intensifies erosional forcing along the coast and at the seaward margin of mangrove forests. The effect is particularly pronounced under conditions of sediment deficit, where the reduced capacity for sediment replenishment limits the system’s ability to offset erosive losses, thereby promoting a net retreat of the shoreline.

Mangrove ecosystems are especially sensitive to changes in inundation regimes. Sea level rise increases both the frequency and duration of tidal flooding, which can exceed the ecological tolerance of certain species if vertical accretion through sedimentation and organic matter accumulation does not keep pace. In such cases, mangrove stands may experience degradation, thinning, or landward migration, depending on local topography and sediment availability.

In summary, while the absolute rate of sea level rise in the Mekong Delta is moderate, its geomorphic and ecological consequences are amplified by the delta’s low relief and sediment-starved conditions. Sea level rise acts as a persistent, system-wide driver that exacerbates coastal erosion, salinity intrusion, and ecosystem stress, thereby increasing the long-term vulnerability of the delta under ongoing climate change.