Gabriele Arduini, Christoph Rüdiger, Gianpaolo Balsamo
Abstract. Glaciers and ice sheets are critical components of the cryosphere and the climate system. In a warming climate, surface temperatures exceed the melting point more frequently and for longer periods, making ice and snowpacks increasingly susceptible to melting. Meltwater from glaciers and ice sheets contributes to freshwater inputs to oceans and rivers, while the ice and snow surfaces provide a cooling effect on the atmosphere. This study presents a new parameterisation enabling a more realistic representation of glaciers and ice sheets in a global land surface model used for numerical weather prediction and reanalyses, accounting for the seasonal evolution of the snowpack and the fractional glacier coverage within grid points. The new scheme has been tested in stand-alone (offline) mode across various scales, from point-level to regional and global simulations, and validated against in situ observations and a range of reference datasets. Results show improvements in the representation of surface temperature, albedo, and snow processes compared to the current scheme, leading to a more accurate simulation of melting events and surface mass balance for the Greenland Ice Sheet. The impact of the new scheme on the hydrological cycle was also assessed for glacier-fed river basins, for which the increased melting generally leads to higher river discharge. It is shown that it improves simulations for basins with an underestimation of their streamflow generation during summer or early spring. However, this effect can be detrimental in basins where the current model already overestimates the discharge, further amplifying the positive bias. Overall, the new scheme enables a more accurate and physically realistic representation of glacier processes, enhancing the representation of cryosphere surfaces of future climate reanalyses for a wide range of scientific applications.