Impacts of future climatic change (2070–2099) on the potential occurrence of debris flows: a case study in the Massif des Ecrins (French Alps)

In this paper we investigate the impacts of future climatic change on the occurrence of debris flows in the Massif des Ecrins (French Alps). Two distinct aspects are discussed: the impact of future climatic change on the evolution of the process, and changes in the spatial distribution. Three climate simulations are presented for the current period (1970–1999) and for future periods (2070–2099) using GCM ARPEGE CLIMAT model developed by Météo-France. Simulated data are then statistically downscaled to obtain a higher spatial resolution. In the first step, we compare occurrence probabilities in the current period and in the next century. In the second step, we estimate which zones would be affected by the process in the future at the scale of the Massif des Ecrins. For the current period, the best model was obtained between debris flows and the number of days between June 15th and October 15th with more than 20 mm calculated either from observed meteorological or simulated data. Results of the ARPEGE model considering the A2 hypothesis (IPCC 2007) showed that the most significant climatic trends for the end of the century will be a decrease in intense rainy events and an increase in temperature. These trends are expected to reduce the occurrence of hill slope debris flows in the Massif des Ecrins. From a spatial point of view, the increase in temperature should result in a shift of the 0°C isotherm to a higher elevation which, in turn, should result in a 20% reduction of the number of slopes affected by the process.