Journal of Glaciology (2018), 64(243) 119–131 doi: 10.1017/jog.2018.7 © The Author(s) 2018. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons. org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Glacier-wide summer surface mass-balance calculation: hydrological balance applied to the Argentière and Mer de Glace drainage basins (Mont Blanc) A. VIANI,1,2 T. CONDOM,1 C. VINCENT,3 A. RABATEL,3 B. BACCHI,2 J. E. SICART,1 J. REVUELTO,4 D. SIX,3 I. ZIN1 1University of Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l’Environnement (IGE) - UMR 5001, Grenoble, France 2Department of Civil Engineering, Architecture, Land, Environment and Mathematics (DICATAM), University of Brescia, Brescia, Italy 3University of Grenoble Alpes, CNRS, Institut des Géosciences de l’Environnement (IGE) - UMR 5001, Grenoble, France 4Météo-France - CNRS, CNRM UMR 3589, Centre d’Études de la Neige (CEN), Grenoble, France Correspondence: Alessandra Viani <[email protected]> ABSTRACT. We present the glacier-wide summer surface mass balances determined by a detailed hydro- logical balance (sSMBhydro) and the quantification of the uncertainties of the calculations on the Argentière and Mer de Glace-Leschaux drainage basins, located in the upper Arve watershed (French Alps), over the period 1996–2004. The spatial distribution of precipitation within the study area was adjusted using in situ winter mass-balance measurements. The sSMBhydro performance was assessed via a comparison with the summer surface mass balances based on in situ glaciological observations − (sSMBglacio). Our results show that the sSMBhydro has an uncertainty of ± 0.67 m w.e. a 1 at − Argentière and ± 0.66 m w.e. a 1 at Mer de Glace-Leschaux. Estimates of the Argentière sSMBhydro values are in good agreement with the sSMBglacio values. These time series show almost the same inter- annual variability. From the marked difference between the sSMBhydro and sSMBglacio values for the Mer de Glace-Leschaux glacier, we suspect a significant role of groundwater fluxes in the hydrological balance. This study underlines the importance of taking into account the groundwater transfers to represent and predict the hydro-glaciological behaviour of a catchment. KEYWORDS: Glacier hydrology, glacier mass balance, mass-balance reconstruction, mountain glaciers 1. INTRODUCTION the knowledge of the interaction between glaciers, climate The role of mountains in sustaining the social and economic and hydrology. In addition, the assessment of meltwater wellbeing of millions of people is well known and unques- runoff is crucial for both water supply and hydropower tioned since snow fields and glaciers provide indispensable applications. water resources for municipal and industrial water supplies, The determination of the glacier mass balances can be irrigation, hydropower production and other environmental obtained using different methods, such as geodetic, glacio- services (e.g., Viviroli and Weingartner, 2004; Barnett and logical and energy balance methods (Cogley and others, others, 2005; Viviroli and others, 2007, 2011). 2011). There are several studies on modelling of glacier Glaciers are considered as one of the most reliable indica- surface mass balance, in the context of providing future pro- tors of climate variations, having either an anthropogenic or jections of runoff from specific glaciers (Immerzeel and natural origin (Oerlemans, 1986; Haeberli, 1995, 2005; others, 2012) and all glaciers worldwide (Marzeion and Johannesson, 1997). Changes in melt rates impact runoff others, 2012). These models are often calibrated/validated dynamics and mainly regulate summer stream flows against glaciological and/or altimetric measurements of (Jansson and others, 2003; Dahlke and others, 2012). glacier mass balance. If such models are used to calculate Therefore, in highly glacierized catchments, glacier melt pro- future runoff, they may be erroneous, as they are not vides an important contribution to the river discharge, par- accounting for inter-basin transfer (i.e. subterranean fluxes). ticularly during the summer (Verbunt and others, 2003; The current study shows the importance of considering the Koboltschnig and others, 2008; Jost and others, 2012). The groundwater fluxes. The method proposed is to estimate the retreat of glaciers could lead to increased hazards, such as glacier-wide summer surface mass balance using the hydro- outbursts of glacier lakes, destabilization of slopes and logical method in two glacierized catchments. Our attention floods. Furthermore, glaciers have been the biggest source is focused on the Argentière and Mer de Glace-Leschaux gla- of the observed sea-level rise since 1900 (Vaughan and ciers, located in the upper part of the Arve watershed at others, 2013) and they will potentially contribute more Chamonix (French Alps). To this end, the glacier-wide strongly to sea-level rise within the 21st century than the summer surface mass balance is obtained using observed ice sheets (Church and others, 2013). For this reason, it is runoff data and the quantification of each term of the hydro- important to have a good understanding of the summer logical balance equation, as well as their uncertainties during glacier surface mass-balance evolution in order to improve the summer season (June, July, August, September, hereafter Downloaded from https://www.cambridge.org/core. 30 Sep 2021 at 21:34:57, subject to the Cambridge Core terms of use. 120 Viani and others: Glacier-wide summer surface mass-balance calculation denoted as JJAS) over the period 1996–2004. Meteorological hydrological and glaciological methods (Section 5) and data are taken from the SAFRAN (Système d’Analyse their comparison (Section 6) will be analysed in detail. Fournissant des Renseignements Adaptés à la Nivologie) (see Section 3.2) reanalysis due to the lack of in situ measure- ments. An adjusted precipitation dataset (adjusted SAFRAN) 2. STUDY SITE has been produced on the base of the SAFRAN reanalysis (ori- The Arve River is an alpine river with a glacial regime that ginal SAFRAN) taking into account the observed accumula- flows mainly through France in the region of Haute-Savoie. tion measurements at each glacier surface. The performance Rising in the Graian Alps, close to the Swiss border, it of the summer surface mass-balance estimations based on receives water from many glaciers of the Mont Blanc massif hydrological data (sSMBhydro) is evaluated by comparing before flowing into the Rhône River. The Arve catchment them with the glacier-wide summer surface mass balances covers a surface area of 2083 km2. This study focuses on based on in situ glaciological observations (sSMBglacio), the upper Arve catchment at Chamonix (Fig. 1a), located over the period 1996–2004. between the Mont Blanc and Aiguilles Rouges massifs. Its This paper will first describe the study sites (Section 2) and surface area is highly glacierized (35% of the total area, in the available data (Section 3). Then, we will focus on the 2003) with three main glaciers located in the eastern part: methodology (Section 4). The estimation of the glacier- Glacier du Tour, Glacier d’Argentière and Glacier de la wide summer surface mass balances obtained with Mer de Glace-Leschaux, covering areas of 8.2, 11.4 and Fig. 1. (a) Location and altimetry of the upper Arve watershed, Arveyron d’Argentière and Arveyron de la Mer de Glace catchments and their respective glaciers (in 2003). The black points and orange triangles respectively indicate the location of the hydrological gauging stations of the two catchments considered and the network of the snow depth gauging stations. The star locates the water intake of the centrale des Bois hydroelectric plant. (b) Mer de Glace-Leschaux (left) and Argentière glaciers (right) with all their tributaries in 2003 (Gardent and others, 2014; Rabatel and others, 2016). The triangles represent the network of the in situ surface mass-balance measurements in both the accumulation (blue) and ablation (red) areas. The different coloured areas indicate the glacier divisions for the computation of the glacier-wide winter glaciological surface mass balance (see Section 4.2). (c) Land cover map of the study area (CLC 06 (Corine Land Cover 2006) (EEA (European Environment Agency), 2007)). (d) Geological map provided by BRGM (Bureau de Recherches Géologiques et Minières). The solid and dotted purple lines respectively represent the main shear zones and their interpolation (Rossi and Rolland, 2014). The pink line indicates the location of the Mont Blanc road tunnel. In figures (c) and (d), the glacier extents are indicative only. Downloaded from https://www.cambridge.org/core. 30 Sep 2021 at 21:34:57, subject to the Cambridge Core terms of use. Viani and others: Glacier-wide summer surface mass-balance calculation 121 31.6 km2 in 2003, respectively (Gardent and others, 2014; 1930; Jamier, 1975). The results are fissure and fracture Rabatel and others, 2016). Here, we focus on the glaciers systems in a N-S and NE-SW direction that primarily stretch that belong to the GLACIOCLIM (Les GLACIers, un across the southern part of the upper Arve watershed Observatoire du CLIMat) observatory (https://glacioclim. (Fig. 1d) (Dubois, 1992; Rossi and Rolland, 2014). It is also osug.fr, Six and Vincent (2014)): Glacier d’Argentière, mon- noticeable that there is a significant