Typhoon-Induced Waves and Storm Surges along Taiwan’s Coast: Historical Trends and Future Projections

Taiwan’s coastal areas are highly vulnerable to typhoon-induced waves and storm surges, posing severe threats to coastal defenses, port operations, and maritime safety. Over the past decade, Taiwan has experienced an average of 4.5 typhoons annually, resulting in wave heights typically exceeding 10 meters, with maximums reaching 23 meters, and storm surges ranging from 20 to 40 cm. Understanding these extreme events under climate change scenarios is essential for effective disaster prevention and coastal planning. This study utilizes EC-Earth3 wind field data from the SSP5-8.5 high-emission scenario to simulate historical (1961–2020) and projected future (2021–2100) typhoon wave and storm surge data, followed by an analysis of their characteristics. Although the EC-Earth3 outputs have a spatial resolution of 100 km and a temporal resolution of 3 hours, this study refined them using an artificial intelligence-based downscaling model. A convolutional recurrent neural network (CRNN) enhanced the resolution to 3 km and 1 hour, enabling more detailed and accurate data for analyzing typhoon waves and storm surges.

Historical analysis reveals distinct regional variations in wave changes around Taiwan. The eastern coast exhibits the largest wave change due to its exposure to the Pacific Ocean, while the Taiwan Strait remains the most stable, predominantly influenced by monsoonal conditions. The southern and northern waters show intermediate wave change levels, with the latter affected by shifting typhoon tracks. Future projections suggest moderate increases in wave heights around Taiwan, particularly in the northern and northeastern waters, driven by the northeast monsoon and typhoon activity. These findings underscore the increasing risks to Taiwan’s coastal regions under changing climate conditions. This study further examines the regional characteristics of design wave heights, revealing the differential impacts of climate change on extreme wave conditions. Wave conditions in the Taiwan Strait are predominantly influenced by monsoons, with minimal climate change effects and relatively stable future design wave heights, ranging from approximately 3.63 to 3.68 meters for projected scenarios. In contrast, the eastern coastal waters, affected by typhoons and the Kuroshio Current, display moderate variability, with historical wave heights ranging from 4.42 to 4.92 meters and projected heights from 4.08 to 4.22 meters. The northern coastal waters show the most significant increases, with future wave heights reaching up to 5.65 meters for a 200-year return period. Meanwhile, the southern coastal waters exhibit limited changes, with future wave heights remaining stable between 5.21 and 5.26 meters, reflecting distinct regional response patterns to extreme wave conditions.

Storm surge simulations reveal additional risks. Historical records indicate that storm surges typically range from 10 to 30 cm, with peaks exceeding 40 cm during extreme typhoon events. Future scenarios indicate an increased frequency of extreme surges surpassing 40 cm, with localized peaks exceeding 50 cm, compounding risks when combined with large waves. These findings provide a scientific foundation for developing a joint probability distribution model for wave heights and storm surges, leading to the establishment of a Coastal Impact Index (CII) that quantifies the combined effects of waves and storm surges during typhoons.