Mémoire

Abstract

With global warming, supra-glacial lakes (SGLs) are increasingly widespread on the Greenland Ice Sheet (GrIS) due to enhanced meltwater runoff and ablation zone extension. However, SGLs as well as all associated hydrology are currently neglected by models simulating the evolution of the Surface Mass Balance (SMB) of the ice sheets. These models assume that meltwater runoff is directly transferred to the ocean as soon as the snowpack is liquid water-saturated, regardless of the location of this meltwater on the ice sheet or topography. Nevertheless, the presence of SGLs on the surface of the ice influences the SMB. Notably by its predisposition to retain liquid water (that could refreeze in winter) or to generate extra evaporation in summer or by its low surface albedo, locally increasing the absorption of solar energy. To evaluate the importance of SGLs as a potentially significant SMB component, we ran MARv3.14 at high resolution (5km×5km) over South-West Greenland for the 2018-2019 hydrological year. We conducted sensitivity experiments to examine the effects of this surface water on bare ice albedo, evaporation, meltwater retention, and atmospheric feedback. Surface meltwater in the ablation zone was allowed to remain liquid or solid in bare ice areas where SGLs were detected by satellite. Additionally, we carried out a quantitative study of SGLs in Greenland using primarily LANDSAT 8 data. We conclude that modifying the runoff parameters in the Modèle Atmosphérique Régional (MAR) model can significantly alter the modelled SMB. Also, improving the treatment of runoff in the model is essential for better quantifying the impact of supraglacial hydrology on the SMB.