Development of Return-Period-Based Extreme Sea Level Maps along the Korean Coast

Coastal regions are projected to experience a continuous increase in storm surge heights due to climate change–induced mean sea level rise and the intensification of typhoons. These changes substantially exacerbate the risk of coastal inundation in low-lying areas, necessitating a reassessment of existing design standards and disaster mitigation frameworks. To proactively respond to the evolving coastal inundation environment, it is essential to move beyond deterministic design approaches based solely on historical maxima and instead adopt probabilistic analyses of Extreme Sea Levels (ESLs). This study was conducted as part of a project in Korea aimed at developing storm surge–induced coastal inundation prediction maps. A total of approximately 4,100 ESL datasets for each return period, derived through computation and analysis for return periods of 50, 100, 150, and 200 years over a 13-year period (2011–2024), were used to construct spatial distribution maps of ESL heights along the entire Korean coast. To minimize inconsistencies arising from temporal and regional differences in reference sea levels, all ESLs were standardized to a common datum based on the Approximate Highest High Water (AHHW) referenced to the mean sea level at Incheon. For coastal areas where inundation prediction maps were not available, ESLs were estimated using frequency analysis based on the Gumbel distribution. To evaluate the reliability of the constructed ESL distribution maps, the estimated ESLs were compared with ESLs derived from observed tide gauge records, as well as results from extreme value analyses based on the Empirical Simulation Technique (EST) and the Annual Maximum Series (AMS) approach. The comparisons showed similar magnitudes and spatial distribution patterns across regions and return periods, indicating overall consistency in the estimated ESL characteristics. The nationwide coastal ESL distribution maps developed in this study are expected to serve as fundamental baseline data for coastal municipalities in the era of climate crisis, supporting the establishment of comprehensive natural disaster mitigation plans, coastal inundation risk assessments, designation of coastal inundation hazard zones, and the design of coastal and harbor structures.