Modelling Shallow Landslides Triggered by Rainfall in Tropical and Mountainous Basins

Shallow landslides triggered by rainfall in tropical environments are controlled by the weathering tropical profile and its water storage capacity. Although landslides triggered by rainfall are common in tropical and mountainous basins, few studies have been applied to the case of tropical regions, which are characterized by intense rainfall and deep weathering profiles. Thus, it is necessary to implement over these areas physical models and methodologies to determine the spatial location of landslides and their susceptibility level. In this work, a conceptual and physically based model called SHIA_Landslide (Simulación HIdrológica Abierta, or SHIA, in Spanish) that is supported by geotechnical and hydrological features occurring on a basin-wide scale in tropical and mountainous terrains is described. This model incorporates a comprehensive distributed hydrological tank model that includes water storage in the soil coupled with a classical infinite-slope stability analysis under saturated conditions. Additionally, this work presents the analyses and results of the implementation of the SHIA_Landslide model to estimate the landslides caused by a rainfall occurred on September 21st, 1990, in a basin of tropical and mountainous terrains of Colombian Andes. In less than 3 h, a precipitation of 208 mm fell within the study area, triggering more than 800 landslides. The results obtained by the model are compared with a landslide inventory presented during the event. Finally, the efficiency of SHIA_Landslide is evaluated in terms of landslide density and susceptibility classes (degree of fit and success-rate curve), and the prediction capacity by ROC (Receiver Operating Characteristics) analysis. It is possible to show a good performance of the model suggesting that SHIA_Landslide is able to simulate the physics involved on landslides triggered by rainfall in tropical and mountainous terrains.