Comparing the Yangtze and Mississippi River Deltas in the light of coupled natural-human dynamics: Lessons learned and implications for management

The Yangtze River Delta (YRD) and Mississippi River Delta (MRD) are two of the largest deltas in the world. Despite similar forcing conditions of fluvial sediment reduction and relative sea-level rise, there are significant differences in deltaic change caused by hydrodynamics and human activities. In this review, we compare the morphological changes of the two deltas at multiple spatial and temporal scales and identify the lessons learned from past engineering and management strategies. While the YRD has seen an increase of subaerial land of ~1500 km² since 1950, the MRD has lost approximately 5000 km² of land since the early 1930s. Extensive land reclamation and coastal shoreline embankment in the YRD have led to land gain at the expense of tidal wetland shrinkage. In contrast, flood control, waterway transportation, and petroleum industry in the MRD have resulted in levee construction and canal building, which together with subsidence and sea-level rise, have led to significant wetland loss in the MRD. The tidal forcing in the YRD is much stronger than that in the MRD, which has played a role in redistributing subaqueous sediment back into the delta plain, offsetting the negative effect of fluvial sediment reduction. In contrast with continuous population increase on the YRD, wetland loss and exposure to flooding hazards have resulted in population loss on the MRD. These comparative analyses reveal that nature and human interventions have acted together in shaping the modern deltaic morphology. Using the Driver-Pressure-State-Impact-Response (DPSIR) analysis framework, we propose a conceptual model to provide holistic understanding of the natural-human coupled delta system and management strategies, which could yield broad implications for coping with the future challenges in global deltas.