A Warning Model of Rainfall Characteristics for Debris Flow Occurrence in Taiwan

Taiwan is located at the junction of the Eurasian Plate and the Philippine Sea Plate and has an extremely complex geological structure, resulting in frequent earthquake activity. Taiwan is situated in the central region of the Northwest Pacific, where typhoons often form and develop during the summer and autumn seasons. The combination of heavy rainfall and earthquakes exposes Taiwan’s mountainous regions to landslides and debris flow disasters, which cannot be completely prevented through engineering measures and significantly impact people's lives and property. Therefore, an effective debris flow warning system is urgently needed. In this paper, the maximum hourly rainfall depth (I_m), the maximum 24-h rainfall amount (R_d) and RI (RI=I_m ✕ R_d) were analyzed, and the relationship between RI and debris flow triggering is presented. The rainfall-based warning model RI was compared with the RTI model, which is currently adopted by the Taiwanese government. The RTI model is defined as the product of hourly rainfall intensity and the sum of the 24h-rainfall depth and prior-rainfall depth. The two models were applied to the Chen-Yu-Lan River Watershed in Nantou County, central Taiwan, to evaluate the debris-flow occurrence probability during several extreme rainfall events. The results show that the RI model can effectively evaluate temporal variations in debris-flow occurrence probability in response to hourly rainfall intensity during a rainfall event.