Abstract: Based on the ERA5（fifth generation ECMWF atmospheric reanalysis of the global climate）reanalysis wind field data driven SWAN（simulation wave nearshore）model, better spatial resolution grid and more refined measured terrain are adopted in the Xisha Islands and Reefs area, and wave simulation is carried out in the islands and reefs area. The results are verified by the measured data located in the Xisha Islands and the Zhongsha Islands. The results show that the model has good wave inversion performance in the islands and reefs area of the South China Sea. We selected Xuande Atoll as the research area and analyzed the overall wave climate of Xuande Atoll using simulation results from 1999 to 2023. The waves have a disstribution pattern with strong northeast and weak southwest in spatial dimension in Xuande Atoll, in terms of time dimension, the wave intensity is strongest in December and weakest in May, it gradually strengthens from May to December, conversely, it gradually weakens. The average significant wave height has a slight decreasing trend in most areas of the atoll (0-0.2% cm·year^-1), and a slight increasing trend in some areas of the reef (0-0.2% cm·year^-1); The 99^th percentile significant wave height shows an increasing trend in most areas (0-0.7% cm·year^-1) and a small decrease in some reef areas (0-0.1% cm·year^-1), indicating that the wind speed in Xuande Atoll is generally weakening, but the impact of extreme weather such as typhoons on Xuande Atoll is increasing. The months with rising and falling trends in Xuande Atoll are all 6 months, with the largest increase in October (0.4-0.8cm·year^-1) and the largest decrease in November (0.4-1.4cm·year^-1); In terms of monthly statistics with an upward trend, the 99^th percentile significant wave height is one month more than the average significant wave height, indicating that the impact of severe weather such as typhoons on Xuande Atoll is increasing year by year. Although trend significance does not always have a high level of confidence, the results in some months are encouraging, with almost the entire study area having a confidence level above 90%, indicating that our conclusions have a certain level of credibility. This has important reference significance for the future development and construction of islands and reefs such as Xuande Atoll.

Key words: SWAN, Islands and reefs, waves, wave climate, Xuande atoll