Multi-Decadal Sea Level Rise along the Korean Coasts Based on L2-Quality Reprocessed Tide Gauge Observations

Sea level rise is a key indicator of climate change and a major driver of coastal flooding and erosion. Reliable assessment of long-term sea level trends requires high-quality, internally consistent observations that account for instrumental changes and vertical land motion. In this study, we present the reprocessing of long-term tide gauge records around the Korean Peninsula to generate Level-2 (L2) delayed-mode sea level height data and assess recent multi-decadal sea level rise from a climate change perspective. Historical tide gauge observations from 21 coastal stations were reprocessed from the beginning of measurements to December 2024 using a comprehensive quality control framework. The reprocessing procedure includes station history investigation, residual comparison, relative sea level difference analysis with neighboring stations, and scientific interpolation of missing or abnormal data. To accurately quantify long-term sea level variability, vertical land motion associated with coastal structures and ground subsidence was evaluated using precise leveling surveys, GNSS-derived vertical displacement, and satellite-based SAR imagery, and applied as corrections to the sea level records. As a result, consistent hourly L2-quality sea level datasets with observation periods exceeding 30 years were reconstructed. Using the reprocessed datasets, sea level rise rates along the Korean coast were estimated. Over the past 36 years, mean sea level has risen at an average rate of 3.17 mm yr⁻¹, corresponding to an increase of approximately 11.5 cm. Regional variability is evident: rise rates of 3.06–3.6 mm yr⁻¹ are observed along the west and east coasts, while the south coast exhibits relatively lower rates of 2.6–3.4 mm yr⁻¹. Decadal analysis for the last 30 years (1995–2004, 2005–2014, and 2015–2024) reveals temporal and regional variations in sea level rise, with periods of acceleration and deceleration depending on coastal region. The reconstructed L2 sea level datasets provide a robust observational basis for climate change assessment, coastal hazard analysis, and ocean–climate interaction studies. The L2 data will be publicly released via the Korea Hydrographic and Oceanographic Agency in the first half of this year, supporting reproducible and policy-relevant sea level research.