Impact of supraglacial lakes on the Greenland Ice Sheet Surface Mass Balance into the regional climate model MAR

The Greenland Ice Sheet is currently one of the primary contributors to the rise of sea levels . The Total Mass Balance (TMB) of the Greenland Ice Sheet can be decomposed into Surface Mass Balance (SMB) and ice discharge (D). At present, both terms contribute approximately equally to mass loss. However, it has been anticipated that surface losses will become more significant in the future (because coastal glaciers will retreat if the ice sheet continues to melt). Our understanding of SMB is currently notably based on polar regional climate models (RCMs) like MAR ("Modèle Atmosphérique Régional"), that simulates most of the different surface processes involved in SMB. However, one potential important process is currently missing in all model based estimates: the role of supraglacial lakes. The excess of meltwater is directly removed from the pixels by assuming that this mass fully runoffes towards the ocean in models until now. These lakes notably impact on the surface albedo of bare ice and could retain a part of produced surface meltwater that can refreeze at the beginning of winter or evaporate during summer (impacting them clouds and precipitation afterwards).

To evaluate the importance of supraglacial lakes as a potential SMB component needed to take into account, we have run MARv3.14 at very high resolution over the South-West of Greenland during the 2018-2019 hydrological year by allowing the produced surface meltwater in the ablation zone to remain liquid or solid above the surface in the bare ice areas where supraglacial lakes have been detected by MODIS.