汶川震区暴雨泥石流发生的降雨阈值

Rainfall thresholds for debris flows occurrence in the Wenchuan earthquake area

搜集了汶川震区暴雨泥石流发生的降雨数据，采用詹氏法和修正法两种雨场分割法对其进行处理，研究了降雨参数（降雨强度、累积雨量和降雨历时）与泥石流发生之间的关系，建立了汶川震区暴雨泥石流发生的降雨阈值模型。结果表明：采用詹氏法和修正法这两种雨场分割方法所获得的降雨参数之间存在差异。两者的累积雨量差异不大，但后者的平均雨强要小于前者，其原因在于修正法改善了詹氏法估计降雨时间过短的缺点，延长了降雨历时。通过分析平均雨强～历时、累积雨量～历时、标准化平均雨强～历时和标准化累积雨量～历时之间的关系，采用单线法建立了汶川震区暴雨泥石流发生的降雨阈值。研究成果在四川省绵竹市清平乡的泥石流灾害事件中进行了应用与验证，结果表明该方法具有合理性和可行性。

Values of rainfall parameters like the cumulative rainfall, the mean rainfall intensity and the rainfall dura- tion, depend on the definition of a single continuous rainfall event. In this study, a revised method is presented for defining a single continuous rainfall event. Using rainfall data collected during the occurrence of debris flows in the Wenehuan earthquake area, single continuous rainfall events and derived values of rainfall parameters are determined with the Jan＇s method and a revised method proposed in this paper. Empirically-based rainfall thresholds for debris flows occurrence （based on the cumulative rainfall, the mean rainfall intensity and the rainfall duration） are assessed following the two methods for defining single rainfall events. The threshold values obtained using the two methods are validated with debris flows events, which occurred in the Qingping town of Mianzhu city in the Sichuan province. Re- sults show that the cumulative rainfall threshold values slightly differ for the two methods. The mean rainfall intensity threshold obtained by the revised method is generally smaller than that of the Jan＇s method. This is due to the fact that the revised method is able to improve the shortcoming of the Jan＇s method often resulting in a shorter duration of a rain- fall event. The revised method proved to be both rational and feasible. The results show that the rainfall thresholds ob- tained by the revised method can be used to predict the debris flows in the Wenchuan earthquake area.