Landslide hydrology: new challenges in landslide prediction

Rainfall-induced landslides are a damaging natural hazard occurring worldwide. Generally, slope failure mechanisms are quite established, as they are related to pore water pressure increase or gradients (either in saturated or unsaturated soil conditions), while the hydrological processes that control the conditions that predispose the slopes to landslide triggering are rarely, or only indirectly, considered. In fact, understanding and modelling these processes, usually developing over spatial and temporal scales much larger than the landslide itself, have been neglected for decades by the scientific community involved in landslide hazard assessment.

More recently, increasing attention has been given to the driving hydrological processes in landslide field research, but several challenging aspects are still open: the inclusion of large scale (in time and space) processes in the assessment of the hydrological balance of the potentially unstable soil mass; the effects of drainage processes through the soil-bedrock interface at slope scale; the mismatch of soil mechanics and hydrological models, in terms of scale and process conceptualization; the inclusion of catchment hydrological information in landslide hazard assessment.

Identification of predisposing hydrological processes in hillslopes and their influence on landslide triggering can significantly improve the predictive performance of landslide models, whatever their application scale (i.e., from hillslope to regional) and level of complexity (i.e., from physically-based distributed to lumped empirical). Recently, studies that consider the role of predisposing hydrological processes in landslide triggering have been rising, and landslide hydrology is progressively establishing itself throughout the scientific community. A brief overview of some significant recent results of landslide hydrology is presented, with specific reference to: assessment of slope water balance for the identification of major hydrological processes predisposing slopes to failure; definition of empirical hydrometeorological thresholds for landslide prediction, by coupling triggering precipitation depth with either antecedent water content at slope scale, or catchment water storage.