Distributed Melt on a Debris-Covered Glacier: Field Observations and Melt Modeling on the Lirung Glacier in the Himalaya

Debris-covered glaciers, especially in high-mountain Asia, have received increased attention in recent years. So far, few field-based observations of distributed mass loss exist and both the properties of the debris layer as well as the atmospheric drivers of melt below debris remain poorly understood. Using multi-year observations of on-glacier atmospheric data, debris properties and spatial surface elevation changes from repeat flights with an unmanned aerial vehicle (UAV), we quantify the necessary variables to compute melt for the Lirung Glacier in the Himalaya. By applying an energy balance model we reproduce observed mass loss during one monsoon season in 2013. We show that melt is especially sensitive to thermal conductivity and thickness of debris. Our observations show that previously used values in literature for the thermal conductivity through debris are valid but variability in space on a single glacier remains high. We also present a simple melt model, which is calibrated based on the results of energy balance model, that is only dependent on air temperature and debris thickness and is therefore applicable for larger scale studies. This simple melt model reproduces melt under thin debris (<0.5 m) well at an hourly resolution, but fails to represent melt under thicker debris accurately at this high temporal resolution. On the glacier scale and using only off-glacier forcing data we however are able to reproduce the total melt volume of a debris-covered tongue. This is a promising result for catchment scale studies, where quantifying melt from debris covered glaciers remains a challenge.

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Debris-covered energy balance model for Imja-Lhotse Shar Glacier in the Everest region of Nepal

The Cryosphere Discussions ◽

10.5194/tcd-9-3503-2015 ◽

2015 ◽

Vol 9 (3) ◽

pp. 3503-3540 ◽

Cited By ~ 6

Author(s):

D. R. Rounce ◽

D. J. Quincey ◽

D. C. McKinney

Keyword(s):

Thermal Conductivity ◽

Heat Flux ◽

Surface Roughness ◽

Energy Balance ◽

Latent Heat ◽

Latent Heat Flux ◽

Energy Balance Model ◽

Balance Model ◽

Glacier Surface ◽

Supraglacial Lakes

Abstract. Debris thickness plays an important role in regulating ablation rates on debris-covered glaciers as well as controlling the likely size and location of supraglacial lakes. Despite its importance, lack of knowledge about debris properties and associated energy fluxes prevents the robust inclusion of the effects of a debris layer into most glacier surface energy balance models. This study combines fieldwork with a debris-covered energy balance model to estimate debris temperatures and ablation rates on Imja-Lhotse Shar glacier located in the Everest region of Nepal. The debris properties that significantly influence the energy balance model are thermal conductivity, albedo, and surface roughness. Fieldwork was conducted to measure thermal conductivity and a method was developed using Structure from Motion to estimate surface roughness. Debris temperatures measured during the 2014 melt season were used to calibrate and validate a debris-covered energy balance model by optimizing the albedo, thermal conductivity, and surface roughness at 10 debris-covered sites. Furthermore, three methods for estimating the latent heat flux were investigated. Model calibration and validation found the three methods had similar performance; however, comparison of modeled and measured ablation rates revealed that assuming a zero latent heat flux may overestimate ablation. Results also suggest that where debris moisture is unknown, measurements of the relative humidity or precipitation may be used to estimate wet debris periods, i.e., the latent heat flux is non-zero. The effect of temporal resolution on the model was also assessed and results showed that both 6 h data and daily average data slightly underestimate debris temperatures and ablation rates, thus these should only be used to estimate rough ablation rates when no other data are available.

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Debris thickness of glaciers in the Everest area (Nepal Himalaya) derived from satellite imagery using a nonlinear energy balance model

The Cryosphere ◽

10.5194/tc-8-1317-2014 ◽

2014 ◽

Vol 8 (4) ◽

pp. 1317-1329 ◽

Cited By ~ 38

Author(s):

D. R. Rounce ◽

D. C. McKinney

Keyword(s):

Thermal Conductivity ◽

Energy Balance ◽

Temperature Gradient ◽

Satellite Imagery ◽

Energy Balance Model ◽

Shortwave Radiation ◽

Balance Model ◽

Thermal Conductivity Model ◽

Nonlinear Temperature ◽

Elevation Model

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.

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Debris-covered glacier energy balance model for Imja–Lhotse Shar Glacier in the Everest region of Nepal

The Cryosphere ◽

10.5194/tc-9-2295-2015 ◽

2015 ◽

Vol 9 (6) ◽

pp. 2295-2310 ◽

Cited By ~ 17

Author(s):

D. R. Rounce ◽

D. J. Quincey ◽

D. C. McKinney

Keyword(s):

Thermal Conductivity ◽

Heat Flux ◽

Surface Roughness ◽

Energy Balance ◽

Latent Heat ◽

Latent Heat Flux ◽

Energy Balance Model ◽

Balance Model ◽

Glacier Surface ◽

Supraglacial Lakes

Abstract. Debris thickness plays an important role in regulating ablation rates on debris-covered glaciers as well as controlling the likely size and location of supraglacial lakes. Despite its importance, lack of knowledge about debris properties and associated energy fluxes prevents the robust inclusion of the effects of a debris layer into most glacier surface energy balance models. This study combines fieldwork with a debris-covered glacier energy balance model to estimate debris temperatures and ablation rates on Imja–Lhotse Shar Glacier located in the Everest region of Nepal. The debris properties that significantly influence the energy balance model are the thermal conductivity, albedo, and surface roughness. Fieldwork was conducted to measure thermal conductivity and a method was developed using Structure from Motion to estimate surface roughness. Debris temperatures measured during the 2014 melt season were used to calibrate and validate a debris-covered glacier energy balance model by optimizing the albedo, thermal conductivity, and surface roughness at 10 debris-covered sites. Furthermore, three methods for estimating the latent heat flux were investigated. Model calibration and validation found the three methods had similar performance; however, comparison of modeled and measured ablation rates revealed that assuming the latent heat flux is zero may overestimate ablation. Results also suggest that where debris moisture is unknown, measurements of the relative humidity or precipitation may be used to estimate wet debris periods, i.e., when the latent heat flux is non-zero. The effect of temporal resolution on the model was also assessed and results showed that both 6 h data and daily average data slightly underestimate debris temperatures and ablation rates; thus these should only be used to estimate rough ablation rates when no other data are available.

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Committed Warming Due to Earth’s Radiative Imbalance Using a Simple 5-Factor Energy Balance Model

SSRN Electronic Journal ◽

10.2139/ssrn.3541353 ◽

2020 ◽

Author(s):

Ronn Smith

Keyword(s):

Energy Balance ◽

Energy Balance Model ◽

Balance Model

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Response of the Energy Balance on the Margin of the Greenland Ice Sheet to Temperature Changes

Journal of Glaciology ◽

10.1017/s0022143000009461 ◽

1990 ◽

Vol 36 (123) ◽

pp. 217-221 ◽

Cited By ~ 25

Author(s):

Roger J. Braithwaite ◽

Ole B. Olesen

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Air Temperature ◽

Sensible Heat Flux ◽

Ice Sheet ◽

Temperature Response ◽

Greenland Ice Sheet ◽

Energy Balance Model ◽

Balance Model ◽

Sensible Heat

AbstractDaily ice ablation on two outlet glaciers from the Greenland ice sheet, Nordbogletscher (1979–83) and Qamanârssûp sermia (1980–86), is related to air temperature by a linear regression equation. Analysis of this ablation-temperature equation with the help of a simple energy-balance model shows that sensible-heat flux has the greatest temperature response and accounts for about one-half of the temperature response of ablation. Net radiation accounts for about one-quarter of the temperature response of ablation, and latent-heat flux and errors account for the remainder. The temperature response of sensible-heat flux at QQamanârssûp sermia is greater than at Nordbogletscher mainly due to higher average wind speeds. The association of high winds with high temperatures during Föhn events further increases sensible-heat flux. The energy-balance model shows that ablation from a snow surface is only about half that from an ice surface at the same air temperature.

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