Estimation of debris flood magnitudes based on dendrogeomorphic data and semi-empirical relationships

Magnitude estimations of hydrogeomorphic processes contain crucial information for hazard assessments and for the understanding of longer term landscape evolution. In this study, we reconstruct magnitudes of debris floods for a torrential catchment in Tyrol by combining dendrogeomorphic time series of events with semi-empirical equations used to predict event volumes. Reconstructed debris flood magnitudes cover eight decades (A.D. 1930-2008) and vary from 2900 to 45,900 m3. We illustrate that magnitude estimates derived from tree-ring data and semi-empirical equations represent a valuable contribution to the documentation and understanding of hydrogeomorphic processes and that they can complement fragmentary time series in small watersheds for periods covering decades up to centuries. Limitations of the approach are mainly inherent to the age and spatial distribution of sampled trees and may thus influence reconstructed event magnitudes as one goes back in time.