The role of snow and spring moisture conditions in terms of geomorphic activity inferred from tree-ring based chronologies in Central European mid-mountains

Abstract

The role of snow is underrated in the dendrogeomorphic research in terms of the interpretation of the climate factors responsible for the geomorphic activity. We analysed snow parameters and the combined effect of spring and summer climate variables to interpret their role in debris flow/flood and flow-like landslide initiation in two Central European mid-mountain regions. We revisited the tree-ring based chronologies based on a total of 1043 trees for four debris flow/flood catchments and four flow-like landslide bodies. Three approaches were used to determine the event year, including a floating event-response index and different weighted index thresholds. In addition, data from precipitation and streamflow gauges were used to identify the best indicators of rapid snow melting and find the best explanatory climate factors during event years using logistic regression. We identified 24–40 event years with hydrogeomorphic activity and 10–29 years with flow-like landslide reactivations during 1961–2017. The amount of melted snowpack and rain-on-snow during spring were considered the best rapid snowmelt parameters obtained from the precipitation gauges due to highest correlations with the stream gauge data (R = 0.69–0.70). We identified very likely rapid snowmelt in seven debris flow/flood event years and six landslide event years since 1981. Furthermore, high maximum snowpack in spring combined with extreme one-day rainfall in summer were the best explanatory factors for hydrogeomorphic activity, but probably not during the high-magnitude debris flows, which were more dependent on the extreme summer rainfall alone. Landslide reactivations were most likely to occur during years with extreme one-day rainfall events in May to September preceded by a wet period since the last day of continuous snow cover. This study defines a step-by-step procedure to reveal the role of snowmelt and antecedent precipitation in dendrogeomorphic research and shows likely scenarios of geomorphic activity typical of the study area.