Backwasting rate on debris-covered Koxkar glacier, Tuomuer mountain, China

A physically based energy-balance model with improved parameterization of solar radiation for a sloped ice surface has been developed to estimate the backwasting rate of an ice cliff in a debris-covered area. The model has been tested against observations between 5 August and 5 September 2008 on 38 ice cliffs in the debris-covered area of Koxkar glacier, Tuomuer mountain, China. We calculated that the energy-balance model gave a good estimate of the backwasting rates, with errors in the range +/- 1.96 cm d(-1) and root-mean-square errors of 0.99 cm d(-1). Errors arising from setting of surface albedo and turbulent flux parameterization were limited. We found that shortwave radiation is the most important heat source for ice-cliff ablation, contributing about 76% of the total heat available for ice melt, while the sensible heat flux provides nearly 24% of the total heat for ice-cliff wastage. The latent heat flux and net longwave radiation are comparatively small according to the model calculation. The mean backwasting rate of ice cliffs in the debris-covered area of Koxkar glacier is estimated at 7.64 m a(-1) when the winter ablation is neglected. With this annual backwasting rate and given a mean slope angle of 46.4 degrees, the backwasting of ice cliffs produces about 1.60 x 10(6) m(3) of meltwater, accounting for about 7.3% of the total melt runoff from the debris-covered area.