Projection of future high-tide flooding frequency along the coasts of Jiangsu and Shanghai, China

IntroductionHigh-tide flooding (HTF) is becoming an increasingly frequent coastal hazard under accelerating sea-level rise (SLR), yet the combined influences of tidal evolution and non-tidal hydrodynamic processes on future HTF remain insufficiently quantified along the Chinese coast. This study investigates future HTF evolution at six tide gauge stations along the coasts of Jiangsu and Shanghai, spanning the western Yellow Sea and the Yangtze Estuary.MethodsA multi-factor statistical prediction framework was developed by decomposing historical water levels into multiple physical components and constructing four nested HTF prediction models. These models were used to quantify the individual and combined effects of SLR, tidal-amplitude amplification (TA), and non-tidal residuals (NTR) under different emission scenarios.ResultsThe results show that SLR is the dominant long-term driver of increasing HTF frequency, with the most rapid increase occurring under SSP5-8.5. However, TA and NTR exert strong regional modulation on HTF evolution. Tidal amplification is most pronounced at Lianyungang and Yanwei due to the convergent morphology of Haizhou Bay, with tidal amplification alone contributing up to 124 additional HTF days/year at Lianyungang by 2100. In contrast, tidal amplification at Wusong remains weak because of runoff regulation and frictional dissipation in the Yangtze Estuary. NTR contributions are strongest along the central Jiangsu coast, particularly at Sheyang, where NTR contributes up to 137.9 additional HTF days/year under SSP5-8.5. When all three factors are combined, HTF risk exhibits strong spatial heterogeneity, with Lianyungang emerging as the highest-risk hotspot and Wusong remaining comparatively less sensitive. These findings indicate that future HTF evolution along the Jiangsu–Shanghai coast is controlled not only by regional SLR but also by local geomorphology, tidal dynamics, and estuarine hydrodynamics. By explicitly incorporating tidal-amplitude evolution and quantitatively separating the relative contributions of SLR, TA, and NTR, this study provides scientific support for regionally differentiated coastal adaptation, flood-risk management, and dynamic resilience planning under future climate change.