Effect of El Niño on Summer Extreme Ocean Waves over East Asian Regions

Abstract Extreme wave events with devastating impacts on East Asian (EA) coastal regions have recently been more variable. However, despite being a prominent extreme spot due to the influence of anomalous seasonal atmospheric and remote climate variability, the investigation of EA extreme wave attributes, such as duration and intensity, and their relation to the climate events remains unclear. By applying the peaks-over-threshold (POT) method with a fixed threshold set at the 99th percentile, this study aimed to quantify the duration and intensity of EA extreme wave events in boreal summer from 1980–2021 and investigate the influence of El Niño and Pacific Decadal Oscillation (PDO) as the main climate mode in the Pacific Ocean. Spatially, the findings demonstrated that extreme waves have occurred with an intensity up to 1.5 m, persisting in a range from 8 to 35 hours over the study and revealing the prominent spot in the southern part of the study area, impacting the southern coast of Korea. Based on the area-averaged over the prominent spot, the appearance of El Niño induces longer (with an average of 85 h) and more intense summer extreme waves (with 2 m of max intensity). The results suggest that the eastward shifting of tropical storms (TS) due to the El Niño-induced anomalous westerlies at 5°N–10°N contributes to this condition. Furthermore, a positive PDO strengthens the El Niño effect, with the almost doubled in duration, through strong anomalous anticyclonic formation in the Philippine Sea. The study findings enhance our understanding of the link between ENSO and TS activity with respect to extreme wave duration and intensity; these factors can be relevant in formulating plans for mitigating the impact of extreme wave events on coastal environments.