Abstract
Abstract. Debris thickness is an important characteristic of debris-covered glaciers in the Everest region of the Himalayas. The debris thickness controls the melt rates of the glaciers, which has large implications for hydrologic models, the glaciers' response to climate change, and the development of glacial lakes. Despite its importance, there is little knowledge of how the debris thickness varies over these glaciers. This paper uses an energy balance model in conjunction with Landsat7 Enhanced Thematic Mapper Plus (ETM+) satellite imagery to derive thermal resistances, which are the debris thickness divided by the thermal conductivity. Model results are reported in terms of debris thickness using an effective thermal conductivity derived from field data. The developed model accounts for the nonlinear temperature gradient in the debris cover to derive reasonable debris thicknesses. Fieldwork performed on Imja–Lhotse Shar Glacier in September 2013 was used to compare to the modeled debris thicknesses. Results indicate that accounting for the nonlinear temperature gradient is crucial. Furthermore, correcting the incoming shortwave radiation term for the effects of topography and resampling to the resolution of the thermal band's pixel is imperative to deriving reasonable debris thicknesses. Since the topographic correction is important, the model will improve with the quality of the digital elevation model (DEM). The main limitation of this work is the poor resolution (60 m) of the satellite's thermal band. The derived debris thicknesses are reasonable at this resolution, but trends related to slope and aspect are unable to be modeled on a finer scale. Nonetheless, the study finds this model derives reasonable debris thicknesses on this scale and was applied to other debris-covered glaciers in the Everest region.
Highlights
Debris-covered glaciers are common in the Everest area of the Himalayas
We report a method for deriving the debris thickness of debris-covered glaciers using an energy balance model with Landsat7 Enhanced Thematic Mapper Plus (ETM+) satellite imagery and apply the method in the Everest region of Nepal
The model described in this study allows the debris cover or thermal resistance on debris-covered glaciers to be derived from Landsat7 satellite imagery in conjunction with meteorological data from an automatic weather station nearby
Summary
Debris-covered glaciers are common in the Everest area of the Himalayas. The debris cover has a large impact on the sub-debris ablation rate and the evolution of the glacier. Many studies have modeled the energy balance on debris-covered glaciers with varying levels of success (Nakawo and Young, 1982; Nakawo et al, 1999; Han et al, 2006; Nicholson and Benn, 2006; Mihalcea et al, 2008b; Reid and Brock, 2010; Reid et al, 2012; LeJeune et al, 2013) These models integrate meteorological data from automatic weather stations with knowledge of the debris cover to solve for the surface temperature of the debris, which may be used to calculate the sub-debris ablation rates. The model is applied to other glaciers in the Everest region
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