Abstract:Based on hourly precipitation data from the National Meteorological Information Centre of CMA, combined with the diversity of the terrain, the temporal and spatial characteristics of hourly precipitation, as well as characteristics of different types of heavy rainfall event (HRE) before (1992-2002) and after (2003-2021) the impoundment in the Three Gorges Reservoir Area in summer (June-August) are analyzed. The results are as follows. After impoundment, the precipitation and frequency decrease but intensity increases. There is an obvious geographical distribution pattern of precipitation changes, with precipitation, frequency and intensity increasing in the north central part of the Three Gorges Reservoir Area, mostly located in the area north of the Yangtze River, and the precipitation and frequency decrease in the southwest and the intensity weakens in the south central part and northwest of the Three Gorges Reservoir Area, mostly located to the south of 31°N. The spatial difference degree of diurnal peak phases of hourly precipitation before and after impoundment is precipitation intensity>precipitation>precipitation frequency. After impoundment, the stations with increasing trend of precipitation, frequency and intensity become more, and the diurnal peak phases of precipitation and intensity have the feature of phase advance in high altitude mountainous areas. There is no significant change in the precipitation probability and proportion of hourly precipitation at various grades before and after impoundment. The precipitation probability is the maximum at the grade of ［0.1, 0.5） mm, and the minimum at the grade of ≥20 mm. The precipitation proportion shows the maximum at the grade of ［1, 5） mm, the minimum at the grade of ［0.1, 0.5） mm, and about 15% at the grade of ≥20 mm. The diurnal variation characteristics of hourly precipitation after the impoundment are more obvious. The bimodal structures of precipitation and frequency of hourly precipitation at the grade of ≥20 mm are more prominent, while the peak time ranges of precipitation and frequency of hourly precipitation at other grades tend to expand, and the diurnal scale fluctuations of hourly precipitation intensity at each grade are more frequent. Analysis of different duration types of HRE shows that before and after impoundment, the short-duration type of HRE is the highest and the long-duration type is the lowest. The short-duration type of HRE mostly starts in the afternoon, while medium-duration and long-duration types of HRE mostly start at night. After impoundment, the condition is beneficial for HRE maintenance. The probability of short-duration type of HRE starting at noon and in the afternoon increases, and the probability of medium-duration and long-duration types of HRE starting in the morning increase.