The modern Yellow River Delta in transition: Causes and implications

Sustainable development of megadeltas worldwide has recently been the focus of international socioeconomic and environmental concerns. Long-term geomorphic sustainability of deltas is crucial for sustaining coastal resources and marine ecosystems. The modern Yellow River Delta (YRD), which has been developed since 1855, is increasingly facing erosion threats under natural and human-induced changes. Utilizing long-term hydrological data, remote-sensing satellite images and bathymetric survey data, the transition processes of the modern YRD (including both the subaerial and subaqueous delta) during 1855–2015 from the perspective of morphodynamics are examined. The results show that over the past 160 years, the evolution of the Yellow River subaerial delta is under rapid accretion before 2000, and transitioned to slight erosion state after 2000, which is believed to be associated with the reduced sediment supply. Correspondingly, the Yellow River subaqueous delta is also believed to transition from the accretion into net erosion since 2000, with a net volume change rate of −1.5 × 10⁸ m³/yr. As the primary source for deltaic deposits, at least 2.6 × 10⁸ t/yr of sediment supply is required to sustain the erosion-accretion balance of both the subaerial and subaqueous delta. Compared with the previous research, we present that the 160-year morphological evolution of the modern deltaic system is strongly influenced by the reduction of sediment input. Within this time frame the changes in the partition of sediment load among frequent migrations of the deltaic channel could have a direct impact on variations of the long-term erosion-deposition patterns of the modern YRD. Extreme events of storm surges and frequent strong winds caused significant short-term fluctuations in the erosion/deposition of the subaqueous delta that would affect long-term changes. The insights gained from this study may help to set scientific guidelines for the sustainable development of other river deltas worldwide that are subject to climate change and human interventions.