Spatial and temporal distributions of extreme precipitation in the Wujiang River valley and reproducibility analysis

Based on the daily precipitation observation data at 41 meteorological stations in the Wujiang River basin from 1960 to 2016, temporal and spatial distribution characteristics of the annual mean surface rainfall, the annual mean maximum daily precipitation, and the number and precipitation amount of the annual mean extreme precipitation in the Wujiang River basin during the study period were analyzed. The analysis shows the following results. (1) The annual rainfall and the number of raining days in the Wujiang River basin showed a significant increasing trend (both passed the 0.05 reliability test), while the intensity of the rainstorm showed no significant increase. The rainfall and the number of days of rainstorms from May to October were basically the constant. From mid-May to early August, there was a unimodal distribution; the intensity of rainstorm first increased and then decreased. (2) In the past 57 years, the annual mean maximum daily precipitation in the Wujiang River basin did not show significant linear variation, but the interdecadal changes were more obvious. (3) The mean annual number of extreme persistent heavy rainfall in the Wujiang River basin showed an insignificant decrease, but the extreme persistent heavy precipitation showed an insignificant increase. The maximum daily precipitation at five representative stations in Wujiang River basin was calculated using the Gumbel extreme value Ⅰ distribution method. It was found that there was a critical point of 50 a in the time scale of the return period.