The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

The western tropical Pacific is one of the world's regions most severely affected by flood disasters caused by extreme sea level changes. Existing research generally considers extreme sea level changes in this region to be the result of sea level rise, combined with the effects of tides and storm surges. These studies often overlook the important role of interannual and decadal climate variability (such as the El Niño-Southern Oscillation and Pacific Decadal Oscillation) in modulating the frequency and intensity of extreme sea level events. This study, based on hourly tide gauge data, adopts a novel decomposition method to identify and quantify the contributions of different sea level components (tides, storm surges, seasonal cycle, interannual-to-decadal climate variability, and long-term sea level change) to extreme sea level events in the western tropical Pacific. We find that the relative importance of each component to extreme sea level events varies significantly across space and time. the phase transitions of interannual-to-decadal climate variability dominate the low-frequency changes in extreme sea levels at certain stations. At certain observation stations, the phase transitions of interannual-to-decadal climate variability dominate the low-frequency changes in extreme sea levels. This phenomenon is particularly significant for individual extreme sea level events and is more pronounced in island regions compared to coastal areas. In contrast, tidal anomalies have a significant impact on extreme water levels in coastal areas but have a relatively limited effect on island regions.

western tropical Pacific, extreme sea level, El Niño, storm surges