Heavy rainfall concentration changes in South China during the first rainy season of 1965 - 2016

Abstract

Abstract The first rainy season in South China (SC) is a concentrated precipitation season, however, it is unclear that in such concentrated precipitation season, characteristics of heavy precipitation concentration degree in SC during the past 50 years. Based on daily precipitation observation data of 192 stations in SC during the first rainy season (April-June) for 1965–2016, the study investigated and analyzed the temporal and spatial variations of the heavy precipitation concentration index (Q index for short). Results showed that the intensity of heavy precipitation over most regions of SC exhibited an increasing trend. The multi-year mean Q index of the heavy precipitation at different stations varied between 0.3 and 0.6, with an average value of 0.375. The heavy precipitation has a concentration trend in the SC inland and western mountain areas and a dispersion trend in the SC coastal area. Notably, both heavy precipitation and the Q index in most inland and western mountain areas showed an increasing trend, denoting a higher flooding risk there. On the other hand, for the duration of heavy precipitation, the 2-day duration of heavy rainfalls had an increasing trend in inland, western Mountain and East Guangdong. The 3-day duration of rainfalls tended to increase steadily in coastal areas and East Guangzhou, and the 4-day duration of rainfalls increased only in the coastal region. In conclusion, the shorter duration heavy precipitation decreased, while the longer ones increased especially in the coast and East Guangdong, which can contribute to the decrease in the Q index but can not denote a decrease in flooding risks. The possible cause may be attributed to the long-duration heavy rainfall that happened in the West Mountain, East Guangdong and Southeast Coast. On the other hand, the frequency and intensity of ongoing heavy precipitation events in coastal cities of South China have increased significantly.