Air temperature distribution and energy balance modelling of a debris-covered glacier

Near-surface air temperature is an important determinant of the surface energy balance of glaciers that is often represented by constant linear temperature gradients in models. Spatio-temporal variability in 2 m air temperature was measured across the debris-covered Miage glacier, Italy, over an 89 day period during the 2014 ablation season using a network of 19 stations. Air temperature was found to be strongly dependent upon elevation for most stations, even under varying meteorological conditions and at different times of day, and its spatial variability was well explained by a locally derived mean linear temperature gradient (MG-TG) of -0.0088°C m-1. However, local temperature depressions occurred over areas of very thin or patchy debris cover. The MG-TG together with other air temperature gradients, extrapolated from both on and off- glacier sites, were applied in a distributed energy balance model. Compared with piece-wise air temperature extrapolation from all on-glacier stations, modelled ablation using the MG-TG increased by 4% using the environmental 'lapse rate'. Ice melt under thick debris was relatively insensitive to air temperature, while the effects of different temperature extrapolation methods were strongest at high elevation sites of thin and patchy debris cover.