Modelling surface mass loss from the Greenland Ice Sheet in response to radiation and lateral meltwater drainage

Shortwave radiation can penetrate a few metres below the surface of an ice sheet, causing subsurface melting which results in the formation of a surface layer of porous ice, called the weathering crust. The weathering crust evolves in response to changing weather conditions, affecting the albedo, the surface and near-surface melting, and the transport of meltwater across the ice-sheet surface. Here, we extend our existing one-dimensional mathematical model for the vertical structure and temperature of the weathering crust to also account for lateral flow of meltwater through the porous crust. This is done using Darcy’s law and a parametrisation for lateral drainage. Our model successfully reproduces observed temperature, porosity and surface lowering on the south-western Greenland Ice Sheet over several years. This enables our model to be used as a tool for predicting future mass loss and weathering crust evolution in a changing climate. We also explore how two key parameters in our model – representing the partitioning of shortwave radiation between surface and subsurface absorption, and the strength of lateral meltwater drainage – affect the ice structure, temperature and mass loss. From this, we demonstrate the importance of accounting for the weathering crust, particularly subsurface radiation, for correctly reproducing observed surface mass loss.