Bias-Aware Screening of Projected Annual Sea-Level-Cycle Amplification Relative to Tidal Range Along East Asian Coastal and Shelf-Sea Margins

Future changes in the annual sea-level cycle (ASLC) may alter the seasonal water-level conditions experienced along coastal and shelf-sea margins. The relative importance of these changes can be assessed by expressing projected ASLC change within the local tidal frame, although tidal range itself may evolve under sea-level rise and coastal change. We combined DUACS historical ASLC range, CMIP6 historical and SSP3-7.0 projected ASLC fields, EOT20 tidal range, and PSMSL tide-gauge observations across East Asia. ASLC/TR was treated as a complementary nondimensional diagnostic rather than a replacement for the separate ASLC and tidal-range fields. A dimensionless bias-confidence-weighted positive ASLC/TR change, denoted BA-SERSI, was calculated to screen locations where projected seasonal sea-level amplification is large relative to the specified tidal frame. Positive projected ASLC change and its tidal-range-normalised counterpart were related but not equivalent (Spearman ρ = 0.8087; n = 20,771); upper-10% hotspot retention was 79.50%, and normalisation changed the median regional rankings of the Yellow Sea and western North Pacific. Under the conditional static-tide reference, the Japan/East Sea sector had the highest regional median BA-SERSI (0.0577) and 95th percentile (0.0902). Its regional rank remained first in bracketing experiments with spatially uniform tidal-range changes from − 10% to + 10%. However, upper-10% grid-cell hotspot retention relative to the static reference declined to 57.99% for a + 5% tidal-range change and 21.66% for + 10%. Thus, the Japan/East Sea sector shows persistent regional sensitivity within the tested range, whereas individual hotspot locations are conditional on future tidal evolution. BA-SERSI is a bias-confidence-weighted screening metric, not a deterministic projection of future exposure, ecological vulnerability, or coastal risk.