How to improve dating quality and reduce noise in tree-ring based debris-flow reconstructions |
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| Institution: | 1. Climatic Change and Climate Impacts, Institute for Environmental Sciences, University of Geneva, Boulevard Carl-Vogt 66, CH-1205 Geneva, Switzerland;3. Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland;1. Dendrolab.ch, Institute of Geological Sciences, University of Berne, 3012 Berne, Switzerland;2. Climatic Change and Climate Impacts, Institute for Environmental Sciences, University of Geneva, 1227 Carouge, Switzerland;3. Faculty of Earth Sciences, University of Silesia, Poland;1. Institut de Géographie Alpine, Laboratoire Politique publiques, Action Politique, Territoire (PACTE) UMR 5194 du CNRS, Université Joseph Fourier, 14 bis avenue Marie Reynoard, 38100 Grenoble, France;2. Institut national de Recherche en Sciences et Technologies pour l''Environnement et l''Agriculture (IRSTEA), UR EMGR, 38402 St-Martin-d''Hères cedex, France;3. UMR6042 Geolab, Université Blaise Pascal, 4 rue Ledru, F-63057 Clermont-Ferrand, France;5. Section of Earth and Environmental Sciences, University of Geneva, rue des Maraîchers 13, CH-1205 Geneva, Switzerland;6. Institute for Environmental Sciences, University of Geneva, 7 route de Drize, CH-1227 Carouge, Geneva, Switzerland;2. Climatic Change and Climate Impacts (C3i), Institute for Environmental Sciences, University of Geneva, 7 route de Drize, CH-1227 Carouge-Geneva, Switzerland;3. Section of Earth and Environmental Sciences, University of Geneva, rue des Maraîchers 13, CH-1205 Geneva, Switzerland;1. Key Laboratory of Land Surface Pattern and Simulation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences (CAS), Beijing 100101, China;3. Dendrolab.ch, Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland;4. Climate Change Impacts and Risks in the Anthropocene (C-CIA), Institute for Environmental Sciences, University of Geneva, Boulevard Carl Vogt 66, CH-1205 Geneva, Switzerland;5. Department F.-A. Forel for Environmental and Aquatic Sciences, University of Geneva, Boulevard Carl Vogt 66, CH-1205 Geneva, Switzerland;6. Key Laboratory of Alpine Ecology, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China |
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| Abstract: | Tree rings have been used to reconstruct the occurrence of debris flows and other mass movements. Identification of past activity was typically based on the presence of growth anomalies in trees, with a focus on scars, stem tilting, trunk burial or apex decapitation. Clear guidelines have been missing so far and the dating of events has only rarely been based on thresholds so as to distinguish signal from noise. In a similar way, the spatial distribution of affected trees has not normally been considered in mass movement reconstructions, and was at best used as a subjective exclusion factor. This study therefore aims at improving dating quality of and reducing noise in debris-flow time series. Based on a dataset of 803 increment cores (385 trees) affected by debris flows, we reconstruct event histories using (i) a classical experts' approach, (ii) a weighted index (Wit) of responding trees as well as (iii) Moran's I and Getis–Ord Local Gi indices. We identify similarities and differences in results and then investigate subsets of the tree-ring sample to define ideal sampling positions on debris-flow cones and guidelines for sample depth. |
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| Keywords: | Tree ring Dendrogeomorphology Debris flow Growth disturbance Getis–Ord Local Gi index |
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