Rainfall-induced shallow landslides and soil wetness: comparison of physically based and probabilistic predictions

Elena Leonarduzzi,Peter Molnar,Brian W Mcardell

doi:10.5194/hess-25-5937-2021

Abstract

Abstract. Landslides are an impacting natural hazard in alpine regions, calling for effective forecasting and warning systems. Here we compare two methods (physically based and probabilistic) for the prediction of shallow rainfall-induced landslides in an application to Switzerland, with a specific focus on the value of antecedent soil wetness. First, we show that landslide susceptibility predicted by the factor of safety in the infinite slope model is strongly dependent on soil data inputs, limiting the hydrologically active range where landslides can occur to only ∼20 % of the country with typical soil parameters and soil depth models, not accounting for uncertainty. Second, we find the soil saturation estimate provided by a conceptual hydrological model (PREVAH) to be more informative for landslide prediction than that estimated by the physically based coarse-resolution model (TerrSysMP), which we attribute to the lack of temporal variability and coarse spatial resolution in the latter. Nevertheless, combining the soil water state estimates in TerrSysMP with the infinite slope approach improves the separation between landslide triggering and non-triggering rainfall events. Third, we demonstrate the added value of antecedent soil saturation in combination with rainfall thresholds. We propose a sequential threshold approach, where events are first split into dry and wet antecedent conditions by an N d (day) antecedent soil saturation threshold, and then two different total rainfall–duration threshold curves are estimated. This, among all different approaches explored, is found to be the most successful for landslide prediction.

Highlights

Landslides are a natural hazard affecting alpine regions worldwide
We explore two approaches for the prediction of landslides and the value of soil wetness in these predictions applied to a regional-scale study in Switzerland
In the second approach we use rainfall–duration threshold curves informed by soil saturation obtained by a high-resolution conceptual hydrological model (PREVAH)

Summary

Introduction

Landslides are a natural hazard affecting alpine regions worldwide. They damage infrastructure and buildings, sometimes leading to loss of life (e.g. Kjekstad and Highland, 2009; Salvati et al, 2010; Petley, 2012; Trezzini et al, 2013; Mirus et al, 2020). Shallow landslides occur when and where the applied shear on the soil–bedrock interface exceeds the shear strength of the soil on a slope. We focus on shallow rainfall-induced landslides, which involve the top layer of the soil, typically less than 2 m thick, and fail instantaneously In such landslides, failure is typically the result of the development of positive pore water pressure in the soil, which decreases its strength Anderson and Sitar, 1995; Highland and Bobrowsky, 2008) This condition is often associated with intense or long-lasting rainfall events that saturate the soil by vertical infiltration and lateral subsurface drainage. The wetness of the soil prior to the triggering rainfall is a key ingredient in slope failure (Bogaard and Greco, 2018)

Methods

Results

Discussion

Conclusion