Abstract
This study examined the conditions that lead to debris flows, and their association with the rainfall return period (T) and the probability of debris flow occurrence (P) in the Chenyulan watershed, central Taiwan. Several extreme events have occurred in the Chenyulan watershed in the past, including the Chi-Chi earthquake and extreme rainfall events. The T for three rainfall indexes (i.e., the maximum hourly rainfall depth (Im), the maximum 24-h rainfall amount (Rd), and RI (RI = Im× Rd)) were analyzed, and the T associated with the triggering of debris flows is presented. The P–T relationship can be determined using three indexes, Im, Rd, and RI; how it is affected and unaffected by extreme events was developed. Models for evaluating P using the three rainfall indexes were proposed and used to evaluate P between 2009 and 2020 (i.e., after the extreme rainfall event of Typhoon Morakot in 2009). The results of this study showed that the P‒T relationship, using the RI or Rd index, was reasonable for predicting the probability of debris flow occurrence.
Highlights
Ten rainfall events that did not trigger debris flows were predicted with P ≥ 0.5; (b) T determined by Rd : four of seven debris flow events were predicted with
This study investigated the occurrence of debris flows after extreme events such as the Chi-Chi earthquake (CCE) and extreme rainfall in a 449 km2 region of the Chenyulan watershed
The probability of debris flow occurrence was analyzed to determine the uncertainty of the hydrogeological conditions in the study area
Summary
This study aims to integrate these rainfall indicators and establish a model for evaluation of the probability of debris flow occurrence
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