Study on Debris Flow Characteristics and Probability After Extreme Rainfall: Case Study on Chenyulan Watershed, Taiwan, China

Debris flow were often triggered by rainfall and other extreme events. The occurrence characteristics and probability of debris flow after extreme rainfall were explored in the Chenyulan watershed in central Taiwan, China, which was affected by the Chi-Chi earthquake and extreme rainfall. The results showed that the critical rainfall intensity to induce debris flow after extreme rainfall events would decrease and then recover the original value. The reduction of critical rainfall intensity and the required recovery period were significantly correlated with the rainfall intensity of extreme rainfall events. The relation model between the occurrence probability of the debris flow <italic>P</italic> and the return period <italic>T</italic> showed that the occurrence probability of the debris flow increased significantly after extreme rainfall events, and the further verification on the <italic>P</italic>-<italic>T</italic> relation showed that the model could better predict the occurrence of debris flow disasters. The rainfall intensity triggering the debris flow before and after earthquakes was significantly different, and the combined effect of earthquakes and extreme rainfall was more apt to trigger the occurrence of debris flow disasters.