Intensifying saline water intrusion and drought in the Mekong Delta: from physical evidences to policy outlooks

In this paper, we investigate the recently intensified saline water intrusion in the Vietnamese Mekong Delta (VMD) by identifying the significant shifts of the backwater effect (BWE) imposed on the rivers, and identified four main environmental pressures for this: riverbed incision due to riverbed mining and dam construction, sea level rise (SLR) and land subsidence (LS). Our analysis is based on the extensive ets of hourly-to-daily hydrological time series from 11 gauge stations across the VMD. Firstly, we show a substantial tidal amplification and increased BWE recently in the VMD through the spectral analysis of the hourly water level data. Secondly, we analyzed the rating curves at the tidal zones and found another compelling evidence that the BWE has increased significantly in recent times especially during the dry season. We conclude that the shift of the BWE regime in the rivers in VMD is mainly due to the lowered water level caused by severe riverbed incision from uncontrolled sand mining in the region and the reservoir sediment trapping at the upstream of the basin. Finally, our study provides a novel comparison across riverbed mining, dam construction, SLR and land subsidence regarding their normalized contributions to the balance between fresh and saline water in the VMD. The computed average rates of river incision and water surface elevation across the VMD, point to the predominance of riverbed incision among the four environmental pressures. Ultimately, we contribute an outlook for cross-disciplinary research directions in the future and underline the need for efficient political reforms to facilitate sustainable transformation of livelihoods to cope with the intensification of salinity intrusion in VMD.