Assessing coastal flooding risk in newly reclaimed areas under the influence of relative sea level rise and multiple drivers

Abstract

Sea level rise, combined with extreme coastal flooding, poses a significant threat to the socio-economic development of coastal areas. Meanwhile, some coastal cities are increasingly reclaiming land seaward to address urban land pressure. However, existing studies have rarely assessed how reclamation-induced exposure growth, subsidence-driven relative sea-level rise, and changing coastal defences jointly reshape coastal flood risk. This study integrates InSAR-derived land subsidence and the 2D hydrodynamic model LISFLOOD-FP to simulate high-resolution coastal flooding for historical and future scenarios (2050 and 2100) under RCP 4.5 and RCP 8.5, using Longgang City, Wenzhou as a case study. Economic exposure and loss risks were further assessed for newly reclaimed areas. The reclamation increased land area and enhanced coastal protection from a 20-year to a 50-year return period. However, the newly reclaimed land remains vulnerable because its low elevation and rapid subsidence offset part of the defence benefit. Relative sea-level rise continues to intensify flood extent and depth, with land subsidence further amplifying inundation. Based on vulnerability function, the expected loss under a 100-year coastal flooding event is estimated to be nearly 509 million USD. These findings highlight the need for subsidence control, adaptive seawall upgrading, and risk-sensitive land-use planning in reclaimed coastal zones.