Abstract
The long-term variation is an increasingly important consideration for the planning of wave energy resources in the context of global climate change. This paper presents an analysis of wave energy densities and their long-term trends around Hainan Island, a key industry and economically prosperous area in the northwestern South China Sea. For this analysis, a numerical model with a maximum spatial resolution of 30 m and a period of 42 years (1980–2021) is constructed. Based on the model, the trend and mutation characteristics of energy are systematically evaluated using the Theil-Sen estimation and the Mann-Kendall test. The results indicate that the energy density exhibits a significant downward trend. However, this trend is not a continuous decline over these years; instead, it changed from growth to decline after a climatic mutation around 1999. This study innovates in revealing, by a typical case, that the changes in wave energy trends before and after a climatic mutation can exhibit significant seasonal and spatial differences. Moreover, these differences can be well explained by the interdecadal variations in environmental factors, such as regional wind and swell fields. Such a trend mutation phenomenon should be particularly noteworthy for energy potential evaluation in specific areas.