Combined Effect of Wind and Rain on Typhoon-Induced Landslide

Landslides which cause numerous casualties and property losses are the crucial natural disaster in Taiwan. Traditionally, typhoon-induced landslides studies mainly focused on the triggering factors, such as geological condition, topographic condition and heavy rainfall. However, typhoons often bring sudden maximum wind which sways trees severely, leading to the soil disturbance which decreasing the slope stability. Moreover, some landslide events occurred on borad-leaved forest along the slopes where were only affected by strong winds of the typhoon and were not particularly affecte by heavy rainfall of the typhoon. In this study, data-driven approach is used to prove that strong winds is one of the important trigger factor, especially strong winds lasting for hours. We examed the significance of the combined rain-wind influence on landslides by Three-dimensional (3D) Histogram and Mann-Whitney U test. The results demonstrated that the wind and rain conditions when a typhoon landslide event occurs are both significantly greater than when no landslide event occurs. And a binary machine learning Random Forest model is constructed to predict the occurrences of landslides based on factors, such as heavy rain, strong winds, traditional geological conditions, and topographical factors. The findings of this study infer that  in addition to heavy rainfall, strong winds is also one of the important factor that may increase or trigger the risk of landslides. Therefore, strong winds can not be ignored when investigating the typhoon-induced landslides.