Journal Article

High‐Tide Flooding Along the China Coastline: Past and Future

Li, S., Liu, L., Wahl, T., Jiang, T., Fang, J.

2023

Overview

Coastal flooding has become a major issue for low‐lying coastal cities in China, and a lot of research has focused on assessing flood risk from storms and associated extreme sea levels. High‐tide flooding (HTF), however, which leads to minor inundation and occurs more frequently as sea level continues to rise has not been assessed comprehensively. Here, we analyze HTF along the China coastline using tide gauge records. We show that the frequency of HTF has increased (Xiamen doubled HTF frequency every 11.5–37.4 years, with the median being 17.5 years). As a result, the cumulative loss ratios of HTF are higher than those of major (or extreme) flooding events in several locations. To gain insights into the processes driving HTF changes, we decompose still water levels that occurred during HTF into five components, including non‐linear trend, interannual to decadal mean sea level (MSL) variability, seasonal MSL cycle, tidal anomaly, and nontidal residuals. It is evident that due to sea‐level rise (SLR) fewer components need to combine to raise the water levels above HTF thresholds. We show that the South China Sea coast already experiences HTF purely driven by high spring tides, and will also see the fastest future increase in the number of tide‐only HTF events. In general, China will experience more HTF days under all warming scenarios as SLRs. This long‐term trend will be modulated by the nodal cycle of ocean tides leading to more rapid increases in HTF in the 2030s and 2050s. Plain Language Summary High‐tide flooding (HTF), which usually occurs during high tides in coastal areas, is one of the most apparent consequences of sea‐level rise (SLR). Analyses of HTF in the past and future have been carried out for the United States, Australia, and Europe, but no comprehensive analysis exists for the coast of China. Here, we analyze HTF along the China coast based on available sea level records. We find, for example, that the frequency of HTF has increased and doubled every 17.7 years. High tidal levels alone will lead to more HTF days due to SLR along the South China Sea coast. In the future, the China coast will experience more HTF days under different warming scenarios, with more rapid increases in the 2030s and 2050s due to long‐term cycles in ocean tides. The analysis presented here advances our understanding of HTF along the China coastline, providing a basis for future research and adaptation planning. Key Points The frequency of High‐tide flooding (HTF) along China coastline has increased, with a doubling time of 11.5–37.4 years in Xiamen Cumulative loss ratios of HTF are higher than those of extreme flooding at several locations China will experience more HTF days under all warming scenarios, with more rapid increases in the 2030s and 2050s

• Publisher: John Wiley & Sons, Inc
• Subject: China coastline / Climate change / Coastal flooding / Coasts / Environmental risk / Extreme weather / Flood risk / Flooding / Floods / high‐tide flooding / Mean sea level / Ocean tides / Sea level / Sea level rise / Seasonal variability / Spring tides / Tidal waves / Tides / Topography / Water levels