Predictive power of hydroclimatic controls on the initiation of rapid alpine sediment mass movements

Rapid movements of sediment mass (e.g. shallow landslides, debris flows, rockfall) pose an imminent risk to settlements, infrastructure and human life in mountain regions. Forecasting such intermittent hazards on a large-scale is still challenging, yet essential to ensure effective risk management. Landslide early warning systems can benefit from the predictive power of dynamic hydroclimatic controls to better anticipate the initiation of these events.

This study characterizes distinct hydroclimatic triggering conditions for rapid alpine mass movements, their exceptionality, and their predictability in time.
We base our analysis on an inventory of ca. 1900 observations of shallow landslides, debris flows, and rockfalls in the Swiss Alpine Rhine basin (approx. 4300 km²) over the past 25 years. Utilizing hydrometeorological time series derived from gridded soil and climate products at a 1×1 km spatial and daily temporal resolution, we retrieve distinct families of predisposing and triggering conditions allowing us to objectively identify different process types. Our results show that a significant proportion of events are not exclusively rainfall-driven: approximately 20% of both shallow landslides and debris flows occurred under the influence of snow cover and snowmelt, suggesting that the hillslope response to precipitation and soil wetness varies seasonally. This underscores the necessity of a multivariate and sequential modeling approach.
In a second step, we expand the methodology into a data-driven modelling framework by employing a recurrent neural network (long short-term memory LSTM). It simulates the probability of mass movements occurring over time by decoding the temporal dynamics of the catchment’s hydroclimatic conditions. We demonstrate the algorithm’s potential to internally reproduce hydrogeomorphic catchment states based solely on input time series of precipitation, temperature, and soil wetness. We report an area under the curve-receiver operating characteristic (AUC-ROC) metric of 0.94 (landslides) and 0.84 (debris flows) for testing.

The findings of this study offer novel insights into hydroclimatic and hydrogeomorphic controls on the predisposing and triggering conditions of rapid alpine mass movements. Modern computational techniques allow to simulate seasonally varying contributions of multivariate hydrometeorological variables to the initiation of such events. This will enable predictions of changes in sediment mass movement distributions under a future climate and will offer an opportunity for plugging into early warning systems for landslides.