A physically based model of the year-round surface energy and mass balance of debris-covered glaciers

Debris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.