On the pattern and rate of centennial delta development and adaptation under the world's largest fluvial sediment supply

River deltas are vital for human development and ecosystems, and understanding their long-term morphodynamics is a prerequisite for better management and adaptation under climate change. The modern Yellow River Delta (mYRD), starting to develop since 1855, is one of the youngest large river deltas on the globe, providing an excellent case exemplifying how a river delta evolves and transitions over a century in response to huge fluvial sediment supply and drastic sediment reduction. In this contribution, we reconstruct mYRD's 170-year morphodynamic development based on the integration of historical maps, satellite imagery, bathymetric and hydrological datasets. In-depth data analyses show continuous delta growth with a seaward shoreline aggradation rate of 197 ± 3 m year⁻¹ and a subaerial area increase rate of 27.1 ± 2.2 km² year⁻¹ in the first 125 years (prior to 1985) under a mean fluvial sediment supply of 1400 Mt year⁻¹. Afterward, a sediment decline of 90% induces a transition change from delta aggradation to degradation, with a subaerial land loss rate of 4.5 ± 0.7 km² year⁻¹ between 1985 and 2002. The subaqueous delta underwent a deposition-to-erosion shift change in 2003, with net deposition and erosion rates of 160 and 440 Mm³ year⁻¹, respectively. The mega-delta buildup rate of the mYRD is outstanding in the global context, showcasing how fast delta development could be under excessive sediment supply. Moreover, the afterward aggradation-to-degradation transition implies the risk of delta erosion and shrinkage once sediment supply reduces to a threshold below which erosion and land loss surpass accretion and land formation. These findings inform the necessity of integrative sediment management strategies to mitigate delta erosion and habitat loss at the decade to century time scales.