The use of multi-source cryospheric datasets to improve the simulation of future icemelt contribution to streamflow in large glaciarized basins

Abstract. The glacierized mountains are impacted by dramatic changes in the context of global warming with large implications for hydrology. However, the projection of icemelt contribution to streamflow remains a complicated task and is subject of large uncertainties, especially when the calibration-validation process was performed with little or no cryospheric data. In this study, we present the integration of a glacier module in the distributed conceptual hydrological model J2000, taking into consideration the evolution of glacier surface in the simulations. A calibration and a validation was done using a large panel of hydro-cryospheric datasets, including glacier mass balance observations and simulations, snow reanalyses, snow-cover by satellites and stream gauges. The calibration-validation was performed by applying J2000-Rhône-glaciers to the entire Rhône basin in the historical period (1976–2022) using the SAFRAN climate reanalysis at 8 km horizontal resolution. The set of parameters identified in the past and meteorological data from 5 “GCM-RCM” chains of climate projections under RCP 8.5 scenario were used to simulate the hydrological response of the Rhône basin under climate change projections (1976–2095). The results show that snowmelt, icemelt and streamflow are satisfactorily simulated by J2000-Rhône-glaciers in the Rhône basin. The projections show a decrease of annual streamflow expected by the end of the 21^st century due to a decrease of precipitation and glacier shrinkage in highly glaciated subbasins. The results of the simulations also show an increase of streamflow in winter but a dramatic decrease in summer mainly due to a change in snow seasonality. The icemelt will become extremely low in Isère, Drac and Durance subbasins, while in the Arve, upper Rhône, and along the Rhône River, the future evolution of icemelt contribution to summer streamflow is very uncertain. Despite these uncertainties, our results suggest that the remaining glaciers will still be crucial to sustain the summer streamflow at the end of the century. However, the peak water may be passed by 2040s in the Arve subbasin, and 2050s in the upper Rhône, and the change in snow seasonality will still threaten the availability of water resources in most of the Rhône subbasins. The use of multi-source cryospheric datasets allowed to gain confidence in the projections of icemelt contribution to streamflow in a large basin in the Alps.