The longest tree-ring based chronology of mass movements in Central Europe and their meteorological triggers

Knowledge of meteorological triggers of mass movements is crucial for determining the degree of hazards, but also for predicting their occurrence. Dendrogeomorphic methods (tree-ring based) have repeatedly provided data on historical landslide activity as a basis for detailed trigger analysis. However, the construction of long dendrogeomorphic chronologies encounters limits in the sensitivity of growth disturbances in trees as well as their age dependence. Moreover, accurate meteorological instrumental data usually do not cover the entire length of long tree-ring based chronologies of landslide movements. To resolve these uncertainties, this study has compiled the longest tree-ring-based chronology of mass movements in Central Europe for Mt. Knehyne in Outer Western Carpathians, spanning more than a quarter of a millennium and based on 228 tree-ring series of disturbed individuals of Norway spruce (Picea abies (L.) Karst.). The resulting chronology is a combination of two subchronologies that we constructed from different tree growth disturbances (reaction wood and tree-ring eccentricity), combining the advantages of both approaches. To identify potential meteorological triggers, we combined instrumental data from the nearest meteorological station together with reconstructed data from the wider landslide study area and documentary records. This gave us a uniquely long overlap of the two datasets across the full length of the mass movement chronology, allowing for more robust results compared to significantly shorter overlays. The studied mass movements followed up to three years of above-mean precipitation and were immediately triggered by short (several days) precipitation extremes. Snowmelt lasting several days to weeks in selected cases further modified this pattern.