Tree rings and debris flows: Recent developments, future directions

The sudden and unpredictable occurrence of debris flows poses major problems in many mountain areas in the world. For a realistic hazard assessment, knowledge of past events is of crucial importance. As archival data is generally fragmentary, additional information sources are needed for an appraisal of past and contemporary events as well as for the prediction of potential future events. Tree rings represent a very valuable natural archive on past debris-flow occurrence as they may record the impact of events in their tree-ring series. In the past few years, dendrogeomorphology has evolved from a pure dating tool to a broad range of applications. Besides the reconstruction of frequencies, tree rings allow - if coupled with spatial positioning methods - the determination of spread and reach of past events. Similarly, the wide field of applications includes the identification of magnitudes and triggers of debris-flow events. Besides demonstrating recent developments in the use of tree rings for debris-flow research, this contribution also provides a short overview on the application of tree rings for other mass-movement processes and highlights further possibilities of the method. Established techniques can be applied to related processes such as debris floods, flash floods or lahars. Data obtained can also be used to calibrate modeling approaches. The impact of past and future climatic changes on debris-flow occurrence is furthermore an important aspect where tree rings can be of help.