Amplified tidal evolution driven by the combined effects of coastal reclamation and climate change in the Yellow and East China Seas

Abstract

Astronomical tides are typically regarded as stationary, but small changes of order −0.1 mm yr−1 have recently been observed in the global open ocean. Continental shelf seas can exhibit significantly larger amplitude trends, although observational evidence remains limited and the underlying mechanisms are rarely understood. By combining tide-gauge records and satellite altimetry, this study identifies the Yellow and East China Seas as regions exhibiting unusually large M2 amplitude trends, exceeding open-ocean trends by more than an order of magnitude and reaching up to ±3.0 mm yr−1 or more, larger than any other comparably sized body of water. Numerical experiments quantitatively demonstrate that these pronounced changes result from the combined effects of coastal reclamation and climate change, including enhanced ocean stratification and sea-level rise, with reclamation providing the largest contribution among the sensitivity experiments considered. These findings suggest that tidal evolution driven by coastal reclamation and climate change should be incorporated into future projections of extreme sea levels to improve coastal risk assessment and mitigation.