Abstract: This study selects a typical urban basin in the southern China, the Qinhuai River basin, to analyze the spatiotemporal evolution and inconsistency frequency distribution of extreme rainfalls expressed in terms of extreme rainfall indicators. The results show that in the Qinhuai River basin of 1979 to 2015, the annual rainfall was increased slightly manifesting an increasing trend in summer and winter and a decreasing trend in spring and autumn. Intensity and frequency of its extreme rainfalls were increased significantly, and the abrupt change point and high value area were consistent with the time point and region of its urbanization pattern evolution. For this typical basin, the Pearson type III distribution was optimal for its extreme rainfall series after consistency correction, with its maximum 1-day rainfall (R1d) and annual total rainfall from days with daily rainfall > 99th percentile (R99p) featured with large non-stationary. In the case of the uncorrected R1d used in calculation, the design values were low. The maximum 3-day (R3d) and 7-day (R7d) rainfalls and annual total rainfall from days with daily rainfall > 95th percentile (R95p) were relatively stable. The areas of high R3d and R95p design values for different return periods were distributed in the lower part of the basin and the upstream Lishui district; the areas of high R7d design value were distributed in the upstream Jurong city. Thus, the superimposed effects of extreme rainfalls in both the upper and lower reaches could impose a high flood risk on the lower reaches.

Key words: urbanized basin, extreme rainfall indicators, non-stationary, frequency distribution, spatial and temporal differences