Rainfall and landslide initiation

Rainfall causes changes in surface and groundwater dynamics that reduce the slope stability conditions and cause landslides. Such phenomena pose serious threats to population and infrastructures. Hence, the prediction of the occurrence of rainfall-induced landslides is a key issue. Evaluation of the relationships between rainfall and landslides can be made using physically-based or empirical approaches. After describing the general characteristics of the two approaches, we discuss a grid-based slope stability model for the spatial and temporal prediction of rainfall-induced landslides. Next, we describe a widely used empirical method for the prediction of landslide initiation, i.e., rainfall thresholds. We describe in detail the frequentist method, which allows defining objective and reproducible thresholds at different non-exceedance probabilities, and the associated uncertainties. Moreover, we depict a quantitative method for the validation of the thresholds. Finally, we illustrate possible applications of landslide early warning systems for the operational forecasting of rainfall-induced landslides.