Abstract
AbstractIce cliffs might be partly responsible for the high mass losses of debris-covered glaciers in the Hindu Kush-Karakoram-Himalaya region. The few existing models of cliff backwasting are point-scale models applied at few locations or assume cliffs to be planes with constant slope and aspect, a major simplification given the complex surfaces of most cliffs. We develop the first grid-based model of cliff backwasting for two cliffs on debris-covered Lirung Glacier, Nepal. The model includes an improved representation of shortwave and longwave radiation, and their interplay with the glacier topography. Shortwave radiation varies considerably across the two cliffs, mostly due to direct radiation. Diffuse radiation is the major shortwave component, as the direct component is strongly reduced by the cliffs’ aspect and slope through self-shading. Incoming longwave radiation is higher than the total incoming shortwave flux, due to radiation emitted by the surrounding terrain, which is 25% of the incoming flux. Melt is highly variable in space, suggesting that simple models provide inaccurate estimates of total melt volumes. Although only representing 0.09% of the glacier tongue area, the total melt at the two cliffs over the measurement period is 2313 and 8282 m3, 1.23% of the total melt simulated by a glacio-hydrological model for the glacier’s tongue.
Highlights
Debris-covered glaciers are common in many mountain ranges of the world, and in the Hindu Kush–Karakoram– Himalaya (HKH) region in particular (e.g. Bolch and others, 2012), but they are rarely studied and poorly understood
A number of recent studies based on remote sensing have suggested that, despite the reduction in melt caused by debris thicker than a few centimetres, as observed in experiments at single points, debris-covered glaciers in the HKH region are losing mass at rates similar to those of debris-free glaciers (Gardelle and others, 2012, 2013; Kääb and others, 2012; Nuimura and others, 2012)
The model includes a physically based model of longwave and shortwave radiative fluxes, that takes into account the interplay between the inclined cliff surface and the complex topography of the surrounding terrain, which affects the shading of shortwave radiation and the emittance of longwave radiation from sky and terrain
Summary
Debris-covered glaciers are common in many mountain ranges of the world, and in the Hindu Kush–Karakoram– Himalaya (HKH) region in particular (e.g. Bolch and others, 2012), but they are rarely studied and poorly understood. A number of recent studies based on remote sensing have suggested that, despite the reduction in melt caused by debris thicker than a few centimetres, as observed in experiments at single points, debris-covered glaciers in the HKH region are losing mass at rates similar to those of debris-free glaciers (Gardelle and others, 2012, 2013; Kääb and others, 2012; Nuimura and others, 2012). This discrepancy has been referred to as the debris-cover anomaly (Pellicciotti and others, 2015). They used the model to calculate ablation at a number of stakes at five cliffs on Miage glacier, Italy, that were monitored in two years, and extrapolated the results to the glacier scale by running the model on every cell of cliff surfaces
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