Analysis of Wave Height and Period in the Yangtze River Delta and Adjacent Waters Based on a 31-Year High-Resolution Wave Hindcast

This study presents a 31-year (1993–2023) wave hindcast using a high-resolution two-domain nested numerical wave model implemented with Simulating Waves Nearshore (SWAN). The spatiotemporal variability and long-term trends of two wave parameters (significant wave height Hs and spectral peak period Tpeak) are systematically analyzed for the Yangtze River Delta (YRD) and its adjacent waters. Validation against in situ buoy measurements confirms that the SWAN model effectively reproduces the regional wave conditions. Results indicate that mean wave conditions are primarily modulated by the Asian monsoon, whereas extreme wave events are predominantly influenced by typhoons. This leads to pronounced differences in spatial patterns and seasonal variability between mean and maximum Hs values. In addition, the regional interannual variations of Hs and Tpeak exhibit different degrees of correlation with the Niño 3.4 index, the Pacific Decadal Oscillation (PDO) index and the Western Pacific Subtropical High Ridge Position (WPSH) Index. Overall, both Hs and Tpeak exhibit positive trends over the study period, and both positive trends shift remarkably between seasons. The positive trends in mean wave conditions are mild during spring and summer but more pronounced in autumn and winter. Statistically significant increases in seasonal mean Hs are identified in parts of the East China Sea (0.35 cm a−1 in autumn) and the southern Yellow Sea (0.27 cm a−1 in winter). Notably, not all trends are positive: the 90th percentiles of both Hs and Tpeak during summer exhibit widespread declining trends, although they are not statistically significant.