Recent evolution of the Mekong Delta and the impacts of dams

As the world's third largest delta and one of the world's most important biodiversity hotspots, the Mekong Delta provides both ecological and food security for its inhabitants. Nevertheless, the delta has been threatened by climate change and human activities, particularly the proliferation of hydropower development across the Mekong Basin since the 1990s. However, compared to the well-studied Holocene Mekong Delta, our understanding of the recent 50-year evolution of the Mekong Delta is not sufficient to address these threats. In this study, we used 43-year Landsat images from 1973 to 2015 to investigate the entirety of the Mekong Delta's shoreline, land area and geomorphological changes. We compiled a new and comprehensive GIS database of the dams and irrigations of the Mekong Basin. The goal was to improve our knowledge of the recent evolution of the Mekong Delta and to link the potential impacts of dams and other factors. Our results show that the Mekong Delta is experiencing a significant decrease in the shoreline progradation rate. Currently, 66% of the entire delta shoreline is under erosion. The erosion segments are mainly located on the eastern side of the Ca Mau Peninsula and northwestern side of the delta in the Gulf of Thailand (GoT). Most parts of the shorelines in the estuarine area are still growing, although river sediment continues to decrease. Geomorphological asymmetries, discontinuous shoreline shifts, and sandy beach-ridge sets can be observed in multitemporal images. The entire Mekong Delta experienced a shift from growing to shrinking around 2005 with the gradual increase of the total accumulated installed capacity of the dams over the entire river basin. In the near future, the realization of planned dams, extension of irrigation, groundwater withdrawal, uncontrolled riverbed mining, delta subsidence, sea level rise, and other factors will accelerate the ongoing delta erosion.