Climate change may neutralize the sediment starvation in mega deltas caused by hydropower dams

Sediment trapping by hydropower dams is one major cause of sediment starvation in global river deltas, but how climate change would influence the damming-induced sediment starvation remains unexplored. The Mekong River is the most important international river in Asia with rich biodiversity and massive hydropower potential. Here, we model the combined effect of climate change and damming on the Mekong River's sediment budget. Our study shows that six mega-dams in China currently reduce the sediment load into the Mekong Delta by 12.1%, while major downstream dams quadruple (49.7%) this reduction. The projected warmer and wetter climate may fully neutralize the impact of China's dams (>60% likelihood) and partially offset the impact of downstream dams. The neutralization effect comes with a notable shift in the sediment regime. In a rapid-change scenario, the basin-wide soil erosion, reservoir sedimentation and river sediment settling have changes of +9%, +36%, -135%, respectively, which degrades regional sustainability, particularly in the lower basin. Novel solutions from the perspective of the water-food-energy-climate nexus are urgently needed to maintain healthy sediment budgets in global mega-rivers including the Mekong River.