Satellite-Derived Shorelines Reveal Typhoon-Driven Erosion and Monsoon-Gated Recovery on the Macrotidal Coast of Fujian, China

Abstract

Satellite-derived shorelines (SDS) reconstruct storm-scale beach change, but their accuracy degrades on macrotidal coasts. The prevailing storm-response and recovery framework, moreover, was built on microtidal, swell-dominated coasts. We combine CoastSat multi-mission shorelines (Sentinel-2, Landsat 7–9, 2015–2026) with EOT20 tidal correction, data-driven slope inversion and an expert-in-the-loop beach registry at five sites on the macrotidal (4–7 m) coast of Fujian, China, validate them against 19 sub-metre reference waterlines (18 yielding paired offsets), and apply them to 19 typhoons. Validation resolves the SDS error into a structure: unbiased near mean sea level, a slope-scaled landward bias of ~7–45 m toward low tide, and undefined below a beach-face/low-tide-flat break near −1.5 m, motivating a tide-gated protocol that cuts series scatter to 7–19 m. Typhoon retreats (median 15–16 m) vary systematically with landfall and embayment geometry, whereas offshore wave metrics and backshore hardening show no consistent event-scale control. Recovery is gated by the monsoon calendar: half-restored within weeks in summer, arrested through the northeast monsoon, and completed only the following March–June. This departs from the exponential recovery of mid-latitude coasts. The protocol and event catalogue provide a template for other macrotidal, typhoon-exposed coasts.