Reconstructing hourly coastal total sea levels and assessing current and future extreme sea levels threats to the Coast of China

Climate-driven sea level rise (SLR) will intensify extreme sea level (ESL) events along China's coast. This study reconstructs continuous hourly total sea level (TSL) by incorporating SLA, tide, storm surge, and wave components, addressing the sparse coverage of tide gauges and their often overlooked extreme events (waves). Using a peak-over-threshold method (thresholds optimised between the 97.00-99.99th percentiles) and a 3-day declustering interval, extreme samples were fitted with generalised Pareto distributions via maximum likelihood estimation. Present-day 1-year return levels exceed 1.6 m at most stations, while centennial return levels surpass 4.1 m at Lusi and Kanmen. Spatial variability is evident, with the East China Sea exhibiting higher extremes (~ 3.9-4.7 m for 100-year events) compared to the Yellow Sea and Bohai Sea (~ 2.7-3.5 m) and the South China Sea (~ 1.7-3.7 m). Under the SSP5-8.5 scenario, centennial return levels rise by 0.83 m by 2100, shifting 100-year events to below 50-year return periods by mid-century and less than 10 years by 2100. This study highlights the urgent need for regional adaptation strategies due to the rising intensity and frequency of extreme events, offering an approach that can be applied to other coastal systems to assess current and future ESL hazards under climate change.