Debris Flow Frequency in a Changing Climate: Evaluating Trigger Conditions using a downscaled Regional Climate Model

Debris flows occur as one of the most significant natural hazards in high mountain regions worldwide, and play a substantial role within the sediment budget. Despite their importance, it remains unclear how their frequency may evolve under changing climatic conditions. Long-term and comprehensive records are essential to detect significant changes in their activity over time. However, such multi-decadal datasets are scarce. As debris flows are predominantly triggered by high-intensity rainfall, the identification of (potential) trigger events from precipitation data presents an alternative, at least for transport-limited debris flow systems with sufficient sediment availability. Due to the lack of long-term precipitation records with sufficient temporal resolution, we employed dynamical downscaling of a Regional Climate Model (RCM) based on the Advanced Weather Research and Forecasting model (WRF). This approach produced a high-resolution dataset with 2x2 km spatial and 15-minute temporal resolution, enabling the analysis of intense rainfall events back to 1850.

We applied this approach to the Horlachtal catchment in Tyrol, Austria, where we have elaborated a debris flow inventory from remote sensing and lichenometric dating that spans the past 170 years. This integrated approach allows us to assess changes in debris flow frequency and their climatic drivers since the end of the Little Ice Age. As the RCM dataset covers much of the Central Alps, the analyses can be extended to other regions, offering broader insights into the development of debris flow frequencies in a changing climate.