Hydro-glaciological behaviour of the Arve catchment in the French Alps : climate variability and consequences on water resources availability

Glacier recession and the anticipation of spring snow melt driven by a warming climate could lead to changes in the hydrological cycle affecting not only the headwater catchments but also the areas downstream. In order to correctly predict the magnitude of future possible changes and to consider appropriate strategies of water management, a good understanding of the interaction between glaciers, climate and hydrology is needed. The aim of this study is to assess the effect of climate variability on the hydro-glaciological behaviour and its consequence on water availability in the Arve River catchment (French Alps) since 1960. It covers 1958 km2 and is composed by five nested catchments (Arveyron d’Argentiere, Arveyron de la Mer de Glace, Arve at Pont des Favrands, Arve at Sallanches and Arve at Bout du Monde), all influenced by glacier and snow melt but characterized by various percentages of glacier cover ranging from 5 to 53%. This research is based on a long dataset of in situ or remote sensing glaciological, meteorological, hydrological and snow cover area data.Trend analyses are performed on the hydrological and meteorological data at all the considered sites. The seasonal cycle of each catchment is fitted using a mathematical function, namely the asymmetric peak model, and changes in the discharge are related to observed changes in the meteorological variables and the glaciers’ evolution. Results point out a contrasting behaviour among the catchments characterized by different glacier covers, showing an increasing trend on the discharge values in highly glacierized catchments (with a glacier cover >30%) and a decrease in the low glacierized ones. The sensitivity of the seasonal cycle to the future climate is evaluated. In the mid-21st century the annual runoff would be reduced by 16% for Arveyron d’Argentiere and 31% for Arveyron de la Mer de Glace. Over the summer season, a detailed quantification of each term of the hydrological balance equation, as well as their uncertainties, on the Argentiere and Mer de Glace-Leschaux drainage basins allows to underline the importance of considering the groundwater transfers to represent and predict the hydro-glaciological behaviour of a considered catchment. Two different distributed temperature index melt models coupled with a linear reservoir discharge model are used on the Arveron d’Argentiere catchment over the 1960–2009 period. The calibration is carried out against discharge only and with a multi- criteria approach considering the discharge, the snow cover area and the glacier-wide annual mass balance values at daily time step. Results demonstrate the suitability of the use of a classical degree day model in simulating the hydro-glaciological behaviour and the subglacial water production of a highly glacierized catchment. A KGE of 0.85 is obtained between the observed and simulate discharge values over the 1960–2004 period. The use of a multi-criteria approach seems to reduce the simulation uncertainties.