The change of precipitation and rainy days in Xisha Waters of South China

Based on the daily precipitation and rainy days data at Yongxing island, Xisha waters, in this study we analyzed the changing trend and periodicity characteristics using the Morlet wavelet method. The results shows that: (1) There is a significant seasonal variation of precipitation and rainy days, which is larger in summer and autumn, and lower in winter and spring. (2) Variation of precipitation in Xisha Yongxing Island is dissimilar to that of rainy days. That is, there is a significant decadal variability of precipitation, while rainy days showed an obvious downward trend during the past 56 years. (3) Precipitation had an obvious large time scale (22-24 a) periodic oscillation. However, rainy days had obvious mid-short period (less 15 years) of periodic oscillations. (4) Seasonal variation of precipitation and rainy days are also different. Precipitation in spring shows an upward trend, but declines in summer. In addition, rainy days show an obvious decrease trend in autumn and winter. Precipitation in spring had an stronger short time scale (4-6 a) periodic oscillation after the 1990s, while the maximum periodic oscillation frequency of the rainy days in summer appeared in a time scale of 8-12 a.