Recent Acceleration of Tidal Amplification in the Vietnamese Mekong Delta: Drivers and Environmental Change Implications
摘要
The Vietnamese Mekong Delta (VMD), a low-lying region covering approximately 43,000 km2 and home to over 19 million people, is highly sensitive to changes in riverine and marine forcings. Previous studies have documented tidal changes in the VMD, but often relied on shorter datasets, limiting the ability to distinguish long-term anthropogenic signals from natural variability. Quantifying these changes, including flood peaks and tidal levels, remains a knowledge gap. This study provides a comprehensive, updated analysis using an extended 45-year dataset (1980–2024) to quantify the recent acceleration of tidal amplification and robustly identify its primary drivers. We applied stationary harmonic analysis to water level time-series from six key hydrological stations and a coastal reference station. The analysis focused on principal constituents (M2, S2, K1, O1), key shallow-water (M4) and the solar annual (SA) constituent representing fluvial influence. Our results reveal a significant decline in the SA amplitude at upstream stations, confirming reduced fluvial dominance post-2000. Conversely, principal tidal amplitudes (M2, K1) have sharply increased in mid-delta and upstream locations since 2000. Simultaneously, decreases in M2 phases indicate faster tidal propagation. Notably, the M4 amplitudes also show amplifications at upstream locations, strongly suggesting that riverbed deepening—driven by in-delta sand mining and sediment starvation from upstream dams—is the primary driver of these change. These hydrodynamic shifts have critical implications for increased high-tide flooding and saltwater intrusion, threatening the delta's sustainability. While stationary analysis proved effective for identifying long-term trends, we recommend future work utilizing non-stationary methods to further explore the nonlinear interactions within this dynamic system.