Climate change impacts on mass-movement activity in the Alps
Recent climate change in the European Alps is now fairly well documented. Even if it has not been constant, with periods of slow temperature increase or even cooling, the warming since the end of the Little Ice Age (∼ 1850) has been marked, and accelerated over the 1985–2000 period. Several studies have documented consecutive decreases in snow precipitation phase, snow depths, snow cover durations or snow water equivalent in many countries of the Alpine space.
Spatial pattern of expected seasonal mean change in the Alpine region for temperature (T) and precipitation (P)
Source: Gobiet et al., 2014.
According to the IPCC report (IPCC, 2014), “the frequency of rock avalanches and large rock slides has apparently increased over the period 1900–2007 (Fischer et al., 2012). The frequency of landslides may also have increased in some locations (Lopez Saez et al., 2013). Mass movements are projected to become more frequent with climate change (Huggel et al., 2010; Stoffel and Huggel, 2012), although several studies indicate a more complex or stabilizing response of mass movements to climate change (Dixon and Brook, 2007; Jomelli et al., 2009; Huggel et al., 2012; Melchiorre and Frattini, 2012). Some land use practices have led to conditions favorable to increased landslide risk, despite climate trends that would result in a decrease of landslide frequency, as reported in Calabria (Polemio and Petrucci, 2010) and in the Apennines (Wasowski et al., 2010). Snow avalanche frequency changes in Europe are dominated by climate variability; studies based on avalanche observations (Eckert et al., 2010) or favorable meteorological conditions (Castebrunet et al., 2012; Teich et al., 2012) show contrasting variations, depending on the region, elevation, season, and orientation”.
Yet, quantifying the impact of the recent changes in mountain climate on mass-movement activity and its future evolution in terms of possible modifications of the frequency and intensity of both ordinary and extreme events remains a rather open questions. Most of the time inconclusive, if not contradictory, studies result from insufficiently long or biased historical chronicles. As a consequence, a realistic determination of future potential hazards and risk, relying on solid and complete time series is not possible.
My research interests focus on the understanding of mass movement and aim at improving knowledge on how climatic changes affect their occurrence in terms of frequency, magnitude and extent.
The originality of this research resides above all in the multiproxy approach based on tree-rings and historical materials used to derive multicentennial highly-resolved spatio-temporal reconstructions of past mass movement activity.
The dendrogeomorphic approach
Trees affected by mass movements record the evidence of geomorphic disturbance in the growth-ring series. As a result, they potentially provide a precise geochronological tool for the reconstruction of the activity of past mass movements. Dendrogeomorphic investigations of mass movement processes typically focus on the occurrence of a limited number of specific GD in tree-ring records to date the occurrence of past event.
Characteristic growth reactions in trees after mass movement disturbance: (A) callus pad overgrowing injuries in larch (Larix decidua); (B) callus tissue and tangential rows of traumatic resin ducts (TRD) around damage in L. decidua; (C) sudden decrease in vessel lumina in birch (Betula pendula) after scar infliction; (D) reaction wood formed from tree tilting in spruce (Picea abies); and (E) immediate and intense decrease in increment of L. decidua after apex decapitation, important loss of branch mass, burial, or root exposure.
A single reaction does not make a geomorphic event – with the exception of rockfalls – and criteria therefore need to be defined for the definition of events and for the exclusion of noise. The required minimal number of GDs for an event to be accepted will depend on the spatial footprint that the process under investigation can leave in the field, and may thus need to be adjusted on a case-by-case basis.
Event-response histograms showing avalanche-induced growth responses from sampled trees on the Pèlerins avalanche path (Chamonix valley). Percentage of trees responding to an event. Stacked bar graphs show the proportion of samples with high-intensity (4–5, dark shading) and low-intensity (1–3, light shading) GD. The brown line demarcates line in (b) demarcates the threshold used for index values (It). The yellow area shows the total number of trees (n) alive each year.
Once event detected, the spatial distribution of trees affected by the same event are used to determine the minimum lateral reach and the minimum runout elevation of reconstructed events.
Reconstructed minimum avalanche extent in the runout zone for the events of (a) 1924, (b) 1931, and (c) 1983 and comparison with historical limits derived from technical reports and photographs. Maps show living trees and all trees showing an event-response for the year of the avalanche.
- Castebrunet, H., N. Eckert, and G. Giraud, 2012: Snow and weather climatic control on snow avalanche occurrence fluctuations over 50 yr in the French Alps. Climate of the Past, 8(2), 855-875.
- Dixon, N. and E. Brook, 2007: Impact of predicted climate change on landslide reactivation: case study of Mam Tor. UK Landslides, 4, 137-147.
- Eckert, N., E. Parent, R. Kies, and H. Baya, 2010: A spatio-temporal modelling framework for assessing the fluctuations of avalanche occurrence resulting from climate change: application to 60 years of data in the Northern French Alps. Climatic Change, 101(3), 515-553.
- Fischer, L., R. Purves, C. Huggel, J. Noetzli, and W. Haeberli, 2012: On the influence of topographic, geological and cryospheric factors on rock avalanches and rockfalls in high-mountain areas. Natural Hazards and Earth System Science, 12(1), 241-254.
- Huggel, C., N. Salzmann, S. Allen, J. Caplan-Auerbach, L. Fischer, W. Haeberli, C. Larsen, D. Schneider, and R. Wessels, 2010: Recent and future warm extreme events and high-mountain slope stability. Philosophical Transactions of the Royal Society A, 368, 1919, 2435-2459.
- Huggel, C.,J.J. Clague, and O. Korup, 2012: Isclimate change responsible forchanging landslide activity in high mountains? Earth Surface Processes and Landforms, 37(1), 77-91.
- Jomelli,V., D. Brunstein, M. Déqué, M.Vrac, and D. Grancher, 2009: Impacts of future climatic change (2070-2099) on the potential occurrence of debris flows: a case study in the Massif des Ecrins (French Alps). Climatic Change, 97(1), 171-191.
- Lopez Saez, J., C. Corona, M. Stoffel, and F. Berger, 2013: Climate change increases frequency of shallow spring landslides in French Alps. Geology, 41(5), 619-622.
- Melchiorre, C. and P. Frattini, 2012: Modelling probability of rainfall-induced shallow landslides in a changing climate, Otta, Central Norway. Climatic Change, 113(2), 413-436.
- Polemio, M. and O. Petrucci, 2010: Occurrence of landslide events and the role of climate in the twentieth century in Calabria, southern Italy. Quarterly Journal of Engineering Geology and Hydrogeology, 43(4), 403-415.
- Stoffel, M. and C. Huggel, 2012: Effects of climate change on mass movements in mountain environments. Progress in Physical Geography, 36(3), 421-439.
- Wasowski, J., C. Lamanna, and D. Casarano, 2010: Influence of land-use change and precipitation patterns on landslide activity in the Daunia Apennines, Italy. Quarterly Journal of Engineering Geology and Hydrogeology, 43(4), 387-401.
- Teich, M., C. Marty, C. Gollut,A. Grêt-Regamey, and P. Bebi, 2012: Snow and weather conditions associated with avalanche releases in forests: rare situations with decreasing trends during the last 41years. Cold Regions Science and Technology, 83-84, 77-88.