Variability of rainfall time distributions and their impact on peak discharge in the Wenchuan County, China

Rainfall characteristics influence the formation of runoff and peak discharge, but there are few studies on the variability of rainfall time distributions and their influence on peak discharge in Wenchuan County. This study analysed the variability of the rainfall time distributions in Wenchuan County by using the Huff curve and their impact on the peak discharge by coupling the HEC-HMS model. A total of 817 rainfall events were collected from Wenchuan County, and most of them were characterized by short rainfall durations. The rainfall time distribution patterns were classified as Quartile I, Quartile II, Quartile III, and Quartile IV, and the variability of the rainfall time distribution for each pattern was analysed based on the probability curves. The variability of the rainfall time distribution in Wenchuan County is significant, but the variability of the same rainfall time distribution in different regions is small. The Huff curve for Wenchuan County was developed, and it can be applied to storm designs in the future. The peak discharges for Quartiles I–IV increased gradually. The trigger response of debris flows for Quartile I is a rapid rainfall-triggering response pattern, and the trigger response of debris flows for Quartile II is an intermediate rainfall-triggering response pattern, but the trigger response of debris flows for Quartiles III and IV is a slow triggering response pattern. The debris flows in the Wenchuan earthquake area were widely triggered by rainfall time distribution patterns of Quartiles I and II.