Rainfall thresholds of debris flows based on varying rainfall intensity types in the mountain areas of Beijing

Abstract

Three strong storms that occurred on July 21, 2012, July 20, 2016, and July 16, 2018 caused severe flooding and debris flows in the mountain areas of Beijing. The detailed records of these storms and the actual occurrence time of the debris flows provide an opportunity for evaluating the thresholds derived from different types of rainfall intensities. Herein, a new rainfall threshold of debris flows is derived from the real-time rainfall intensities in Beijing. In addition, the thresholds are estimated based on the average rainfall intensities over the interval from the beginning of the rainfall to the debris flow occurrence and over the entire rainfall duration. The results show that the various types of rainfall thresholds display significantly different capabilities in terms of separating the storms with positive debris-flow response from those with negative debris-flow response, and the real-time rainfall threshold exhibits the best performance. Moreover, our data indicate that the debris flows in Beijing are triggered by the combined work of rainfall intensity and cumulative precipitation. A debris flow is initiated only when the cumulative precipitation and rainfall intensity simultaneously reach a threshold level.