Detailed Mass Balance and Hydrological Modeling of the Hardangerjøkulen Ice Cap in South-Central Norway

A detailed, physically based snowpack model (Crocus) has been incorporated into the hydrological model WRF-Hydro. This allows for direct surface mass balance simulation of glaciers and subsequent modeling of meltwater discharge from glaciers. To evaluate the new system (WRF-Hydro/Glacier), WRF model simulations were downscaled to 1 km grid spacing to provide meteorological forcing data to the WRF-Hydro/Glacier system at 100 m grid spacing. Evaluation of the WRF downscaling showed that it compared well with in situ meteorological observations for most of the simulation period. The WRF-Hydro/Glacier system reproduced the glacier surface winter/summer and net mass balance, snow depth, surface albedo and glacier runoff well compared to observations. The WRF-Hydro/Glacier system is only activated over a priori designated glacier areas. This glacier area is initialized with observed glacier thickness and assumed to be pure ice (with corresponding ice density). This allows for melt of the glacier to continue after all accumulated snow has melted. Furthermore, the simulation of surface albedo over the glacier is more realistic as surface albedo is represented by snow where there is accumulated snow, and glacier ice when all accumulated snow is melted. The improved estimation of albedo has an appreciable impact on the discharge from the glacier during late summer. The impact of sublimation of blowing snow also has an impact on simulated glacier surface mass balance, snow depth and discharge. We have shown that the integrated snow pack system allows for improved glacier surface mass balance studies as well as hydrological studies.