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Sciences in Cold and Arid Regions ›› 2020, Vol. 12 ›› Issue (5): 261-271.doi: 10.3724/SP.J.1226.2020.00261.

   

Effect of debris on seasonal ice melt (2016-2018) on Ponkar Glacier, Manang, Nepal

Reeju Shrestha,Rijan B. Kayastha(),Rakesh Kayastha   

  1. Himalayan Cryosphere, Climate and Disaster Research Center (HiCCDRC), Department of Environmental Science and Engineering, School of Science, Kathmandu University, Dhulikhel 45200, Nepal
  • Received:2020-04-01 Accepted:2020-08-24 Online:2020-10-31 Published:2020-10-29
  • Contact: Rijan B. Kayastha E-mail:rijan@ku.edu.np

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Abstract:

Supraglacial debris is widely present on glaciers in alpine environments and its distribution greatly affects glacier melt. The present study aims to determine the effect of debris on glacier ice melt on Ponkar Glacier, Manang District, Nepal. We estimated ice melt under various debris thickness using Energy Balance (EB) model and conductive heat flux methods, which are compared with in-situ observations. Four stakes are installed on the glacier at different debris thickness of 11-40 cm. Meteorological data from March 2016 to May 2018 are obtained from the Automatic Weather Station (AWS) installed on the glacier surface at an elevation of 3,881 m a.s.l. for the energy balance calculation. Debris surface temperature and different debris depths are also measured on the glacier. The calculated ablation rates from the conductive heat flux method are 0.9, 1.62 and 0.41 cm/d on pre-monsoon, monsoon and post-monsoon, respectively, with mean debris thermal conductivity 1.04 W/(m?K). The net radiation shows little variation between the seasons, while turbulent heat flux varies in the season. Sensible heat flux was found to be highest in post-monsoon season due to a larger temperature gradient between surface and air.

Key words: debris-covered glacier, thermal conductivity, energy flux, Ponkar Glacier, ice melt, Hindu-Kush Himalaya

Figure 1

(a) Location map of study area, Ponkar Glacier in Manang District, Nepal, with the location of AWS and stakes. (b) Photo of AWS installed in ablation part of Ponkar Glacier"

Table 1

Specifications of instruments installed on Ponkar Glacier"

ParameterSensor typeRangeAccuracy
Air temperatureThermometer/Hygrometer HC2S3-40 to +60 °C±0.1 °C
Relative humidityThermometer/Hygrometer HC2S30 to 100% RH±0.8%
Shortwave radiationKipp & Zonen CNR40 to 2000 W/m2<5% for daily sum
Longwave radiationKipp & Zonen CNR4-250 to +250 W/m2<10% for daily sum
Wind speedR M Young 0150430 to 100 m/s±0.3 m/s
Wind directionR M Young 015043360° mechanical±3°
PrecipitationCampbell Rain gauge0 to 50 cm per hour1% at rates up to 2 (inch per hour)
Debris temperature

DVT4 Supco SL300/400 series and

DV series by Micro DAQ, USA

-40 °C to 70 °C± 0.5 °C
ACR Smart Button Miniature Single-Channel Temperature Data Logger-40 °C to 85 °C± 1.0 °C

Table 2

A list of seasons and periods of data used in this study"

SNSeasonsPeriodsNo. of days
1Pre-Monsoon I22 March 2016 to 3 June 201674
2Monsoon I4 June 2016 to 28 August 201686
3Post-Monsoon I15 November 2016 to 30 December 201678
4Monsoon II1 June 2017 to 30 September 2017122
5Post-Monsoon II1 October 2017 to 31 January 2018116
6Pre-Monsoon II1 February 2018 to 14 May 2018104

Figure 2

Mean hourly variation of air and surface temperatures at AWS averaged over the entire period of record"

Figure 3

Mean daily variations of meteorological parameters at the AWS on Ponkar Glacier (a) Air and surface temperatures (°C), (b) Wind speed (m/s), (c) Incoming shortwave and longwave and (d) Relative humidity (%) and precipitation (mm)"

Figure 4

Mean daily cycle of calculated surface heat fluxes for (a) entire period, (b) pre-monsoon, (c) monsoon and (d) post-monsoon at AWS site. Mean daily cycles of heat fluxes are calculated from hourly heat flux during the study period"

Figure 5

Scatter plots of the first derivative of temperature with time against the second derivative of temperature with depth at 30 cm for (a) entire period, (b) pre-monsoon, (c) monsoon and (d) post-monsoon"

Figure 6

Daily debris temperature on Ponkar Glacier at different depths of the debris layer measured from the surface for (a) All seasons, (b) Pre-monsoon, (c) Monsoon and (d) Post-monsoon seasons. Lines with circles are for 0 cm, squares are for 15 cm and with triangles are for 30 cm from the debris surface at AWS site"

Figure 7

Distribution of average hourly debris temperature from 0 to 30 cm debris thicknesses"

Figure 8

Calculated conductive heat flux during the study period. Discontinuity of data is due to missing surface temperature data"

Figure 9

Comparison of observed melt rates (triangles) with calculated daily ice ablation from energy balance model (squares) and calculated daily ice ablation from conductive heat flux method (circles) in (a) Pre-monsoon, (b) Monsoon and (c) Post-monsoon seasons"

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