2018 CSDMS meeting-108

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Towards a landslide warning concept for Switzerland using rainfall thresholds and multi-scale hydrological modeling

Elena Leonarduzzi, Institute of Environmental Engineering, ETH Zurich Zurich , Switzerland. leonarduzzi@ifu.baug.ethz.ch
Reed M. Maxwell, Integrated GroundWater Modeling Center and Department of Geology and Geological Engineering, Colorado School of Mines Golden Colorado, United States.
Brian W. McArdell, Swiss Federal Institute for Forest, Snow and Landscape Research WSL Birmensdorf , Switzerland.
Benjamin B. Mirus, U.S. Geological Survey, Landslide Hazards Program Golden Colorado, United States.
Peter Molnar, Institute of Environmental Engineering, ETH Zurich Zurich , Switzerland.

Landslides are hazardous phenomena affecting mountainous regions worldwide. Our objective is to develop a Warning System for rainfall-induced shallow landslides in Switzerland, where such a dedicated tool is currently missing. Initially, we focused on empirical rainfall thresholds for landslide triggering based on long-term precipitation data and historical landslide inventories. The results showed that, although precipitation is the main triggering factor, event magnitude (intensity) by itself is not sufficient to explain the occurrence of many landslides. To improve the performance, the antecedent soil moisture prior to the rainfall event has to be taken into account, which we explore using a distributed hydrological model. The overall aim is to understand and quantify (a) the geological and hydrologic conditions critical for landslide initiation and (b) the optimal resolutions for hydrological modelling geared towards landslide prediction.

In fact, while slope stability assessment with a geotechnical model requires high resolution topography, the optimal spatial resolution for the computationally expensive hydrological modeling component remains unknown. To address this question, we conducted numerical experiments for a synthetic digital elevation model (DEM) used to simulate a simplified valley. The DEM is an inclined V-shaped domain and simulations are carried out with the coupled hydrologic-land surface model, ParFlow-CLM, in combination with the infinite slope stability model. We tested different slopes, valley convergence angles, soil layering, and permeability contrasts to assess the effect of spatial resolution on the estimation of antecedent soil moisture and the corresponding Factor of Safety.

These numerical experiments will help inform comparative simulations for real catchments in Switzerland and Colorado, as we explore the potential of using topographic methods for downscaling of the estimated antecedent soil wetness from coarser to fine scales. In particular, we will explore whether or not the soil-topographic index can provide a viable alternative to running the hydrological model at the very high spatial resolutions needed for the geotechnical model.