At the recent Alpine Glaciology Meeting (AGM) 2016 held in Munich we presented some of the ongoing work in the Langtang catchment.
Pascal Egli presented his work on the reconstruction of debris thickness on debris covered glaciers from thermal satellite images and meteorological data via an energy balance approach. We used three previously published methods based on the energy balance to compute debris thickness maps of Lirung Glacier, assess their performance and determined their sensitivity to several input parameters. We developed a new time-integrating energy balance model with which we intend to obtain more accurate estimates of debris thickness by accounting for the heat transport and storage in the debris layer. Debris thickness reconstruction is essential for the determination of melt rates of debris covered glaciers in the Himalayas.
Figure 1: Modelled debris thickness on Lirung Glacier using an energy-balance approach, with distributed surface temperature data from a Landsat 8 image from 23rd October 2015.
Pascal Buri presented a new 3D-modelling approach of ice cliff backwasting. Whereas some supraglacial cliffs remain stable in terms of shape over the melting season, some cliffs flatten considerably and disappear. We tested our physically-based model on selected cliffs on Lirung Glacier in order to simulate cliff evolution over one season. Both atmospheric melt and the interaction with adjacent lakes and debris slopes are implemented. This allows us to dynamically simulate the cliff geometry applying monthly geometric corrections. Simulated volume losses and melt rates for each cliff roughly agree with a TIN-approach used for validation but give also further insight into the inter-annual variability of melt processes and mechanisms behind cliff dynamics.
Figure 2: Simulated ice cliff outlines from May to October for cliffs 1-4. Observed outlines from UAV orthoimage in the background.
Jakob Steiner talked about traces of the Gorkha earthquake from April 2015 left on the cryosphere in the catchment. We could observe that the ice released mainly came from the top ridges pointing at topographic amplification playing a possibly significant role in this case. This could help to assess which hanging ice seracs pose a danger in future earthquakes. The massive deposits on the glacier tongues of two debris covered glaciers in the catchment, could provide a chance to observe how the heterogeneous debris cover develops over time.
Figure 3: The debris surface on Lirung glacier is nearly level on the upper parts after the earthquake. Observing how this surface changes into the hummocky terrain normally observed on such glaciers could provide insights into the general development of debris cover.
In the recent special issue of the Annals of Glaciology on ‘Glaciology in High Mountain Asia’ our research team contributed four papers focused on the surface of debris-covered Lirung Glacier, located in the Langtang Valley in the Nepalese Himalaya.
Variation in environmental lapse rate
In a study of the distributed air and surface temperature of the debris surface (link) we propose to adapt the normally used environmental lapse rate when using off-glacier data for an energy balance of the glacier, as the debris surface heats up much more than the surrounding environment (Fig. 1). We also show that the lapse rate has a diurnal cycle and the relation between air and surface temperature changes between day and night and for the dry and wet season. This has implications for using surface temperature data acquired from satellite products used to determine local air temperature over a debris covered glacier.
An additional paper looking at the wider catchment (link) shows a strong seasonality of the environmental lapse rate. Lateral variability at transects across valley is high and dominated by aspect, with south-facing sites being warmer than north-facing sites and deviations from the fitted lapse rates of up to several degrees.
Steiner J. and Pellicciotti F. (2016), On the variability of air temperature over a debris-covered glacier, Nepalese Himalaya. Ann. Glaciol., 57(71), (doi: 10.3189/2016AoG71A066)
Heynen M, Miles E, Ragettli S, Buri P, Immerzeel W and Pellicciotti F (2016) Air temperature variability in a high elevation Himalayan catchment. Ann. Glaciol., 57(71) (doi: 10.3189/ 2016AoG71A076)
Figure 1: Mean air temperatures measured at the T-Loggers in the daytime (red) and at night-time (blue) in all three seasons (a–c) and from 2012 to 2014 (top to bottom). The lines show the temperatures determined with the ELR from the off-glacier AWS Kyanjing. The plots at the bottom show absolute deviation of each value from the ELR.
Distributed modelling of ice cliffs
Investigating ice cliffs further (link) we developed a first distributed model of cliff backwasting for two cliffs. The physically-based model includes an improved representation of shortwave and longwave radiation, and their interplay with the glacier topography. Diffuse radiation is the major shortwave component, as the direct component is strongly reduced through self-shading. Incoming longwave radiation is higher than the total incoming shortwave flux, due to radiation emitted by the surrounding terrain. We could show a considerably high variability in melt rates across the cliff surface and ice cliff melt to be more than 10 times higher than melt under debris per unit area (Fig. 2).
Buri P, Pellicciotti F, Steiner J, Miles E, Reid T and Immerzeel W (2016) A grid-based model of backwasting of supraglacial ice cliffs over debris-covered glaciers. Ann. Glaciol. (doi: 10.3189/ 2016AoG71A059)
Figure 2: Distribution of daily melt rate (cm w.e.) for cliff 1 (left, NW-aspect) and cliff 2 (right, NE-aspect) for pre-monsoon (PRM), monsoon (M) and post-monsoon (POM) periods.
Modelling of supraglacial lakes
In another study (link) we focus on supraglacial lakes. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces (Fig. 3). We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Supraglacial ponds efficiently convey atmospheric energy to the glacier’s interior and rapidly promote the downwasting process.
Miles E, Pellicciotti F, Willis I, Steiner J, Buri P and Arnold N (2016) Refined energy-balance modelling of a supraglacial pond, Langtang Khola, Nepal. Ann. Glaciol., 57(71), 29–40 (doi: 10.3189/2016AoG71A421)
Figure 3: A conceptual diagram of the energy balance developed for supraglacial lakes.
Seasonal surface velocities
The last study (link) reveals seasonal differences in velocities of Lirung Glacier in detail using cross-correlation feature tracking of imagery from an unmanned aerial vehicle (UAV).The glacier has considerable spatial and seasonal differences in surface velocity, with maximum summer and winter velocities 6 and 2.5 m a–1, respectively, in the upper part of the tongue, while the lower part is nearly stagnant (Fig. 4). UAVs have great potential to quantify seasonal and annual variations in flow and can help to further our understanding of debris-covered glaciers.
Kraaijenbrink PDA, Meijer SW, Shea JM, Pellicciotti F, Jong SM, Immerzeel WW (2016). Seasonal surface velocities of a Himalayan glacier derived by automated correlation of unmanned aerial vehicle imagery, Ann. Glaciol., 57(71), 103-113 (doi: 10.3189/2016AoG71A072)
Figure 4: Surface velocity and flow direction obtained by noise-filtered frequency cross-correlation for the summer (left) and winter (middle) period.
Against the unparalleled backdrop of Everest and Nuptse, the late November sun warms the glaciologist slightly as he prepares for an unmanned aerial vehicle (UAV) survey flight. From his coat pockets he pulls batteries that desperately need to stay warm for full power: batteries for the laptop, camera, and UAV that have been stored in his sleeping bag overnight, when temperatures plummeted below -20 C. He checks the wind. He sets up the flight on his laptop, sends the details to the UAV through a radio transmitter, and heads to the nearby launch location. At 5,350 m above sea level, the air has less than half as much oxygen as at sea level, and it can be difficult to launch the UAV as the air pressure is so low. He breathes heavily — partly due to the oxygen depletion, and partly due to nerves. With the UAV in his hands, he starts the motor, heart racing as the propeller whine reaches an intense pitch. He steps forward to throw the UAV and start the flight. He hopes.
In collaboration with Dr Patrick Wagnon, visiting scientist at ICIMOD and researcher at L’Institut du Récherche pour le Développement (IRD, France), and Dr Dibas Shrestha, Research Scientist at the Nepal Academy of Science and Technology (NAST), ICIMOD Glacier Hydrologist Dr Joseph Shea joined a recent field expedition to Sagarmatha National Park (http://www.icimod.org/?q=20187) to conduct UAV surveys of several glaciers in the region. A total of 730 photos were taken from the senseFly eBee (www.sensefly.com) UAV over six successful flights, and the team collected 56 high-precision ground control points to be used in post-processing. The research may have also set an unofficial eBee altitude record, with a maximum flight elevation of 5,900 m. However, the flight conditions were difficult given the altitude and the unpredictable winds, and the eBee was damaged during the course of the fieldwork.
Data obtained during the research will be used to construct detailed mosaics and elevation models of the study sites. Comparisons of the UAV datasets with satellite imagery and terrestrial photography will be used to examine rates of glacier change, glacier flow velocities, and the role of ice cliffs and ponds in the melt rates of debris-covered glaciers. The research was funded by the UK Department for International Development (DFID), ICIMOD, and Utrecht University. The eBee was generously loaned by FutureWater (Netherlands), who have been assured that it will be sent back to the factory for repairs and testing.
The Annals of Glacioly issue with the theme ‘Glaciology in high-mountain Asia‘ will appear in 2016. A few articles of our research group in this issue are already available online as preprints or are accepted for publication.
- Seasonal surface velocities of a Himalayan glacier derived by automated correlation of unmanned aerial vehicle imagery
Philip KRAAIJENBRINK, Sander W. MEIJER, Joseph M. SHEA, Francesca PELLICCIOTTI, Steven M. DE JONG, Walter W. IMMERZEEL
Debris-covered glaciers play an important role in the high-altitude water cycle in the Himalaya, yet their dynamics are poorly understood, partly because of the difficult fieldwork conditions. In this study we therefore deploy an unmanned aerial vehicle (UAV) three times (May 2013, October 2013 and May 2014) over the debris-covered Lirung Glacier in Nepal. The acquired data are processed into orthomosaics and elevation models by a Structure from Motion workflow, and seasonal surface velocity is derived using frequency cross-correlation. In order to obtain optimal surface velocity products, the effects of different input data and correlator configurations are evaluated, which reveals that the orthomosaic as input paired with moderate correlator settings provides the best results. The glacier has considerable spatial and seasonal differences in surface velocity, with maximum summer and winter velocities 6 and 2.5 m a–1, respectively, in the upper part of the tongue, while the lower part is nearly stagnant. It is hypothesized that the higher velocities during summer are caused by basal sliding due to increased lubrication of the bed. We conclude that UAVs have great potential to quantify seasonal and annual variations in flow and can help to further our understanding of debris-covered glaciers.
- Refined energy-balance modelling of a supraglacial pond, Langtang Khola, Nepal
Evan S. MILES, Francesca PELLICCIOTTI, Ian C. WILLIS, Jakob F. STEINER, Pascal BURI, Neil S. ARNOLD
Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of Debris-covered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier’s hydrologic system during the monsoon. Melt rates are 2–4 cm d–1 (total of 98.5 m3 over the study period) for bare ice in contact with the pond, and <1 mm d–1 (total of 10.6 m3) for the saturated debris zone. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits, delivering sufficient energy to melt 2612m3 additional ice over the study period (38.4 m3 d–1). Such melting might be expected to lead to subsidence of the glacier surface. Supraglacial ponds efficiently convey atmospheric energy to the glacier’s interior and rapidly promote the downwasting process.
- A grid-based model of backwasting of supraglacial ice cliffs over debris-covered glaciers
Pascal BURI, Francesca PELLICCIOTTI, Jakob F. STEINER, Evan S. MILES, Walter W. IMMERZEEL
Ice cliffs might be partly responsible for the high mass losses of debris-covered glaciers in the Hindu Kush–Karakoram–Himalaya region. The few existing models of cliff backwasting are pointscale models applied at few locations or assume cliffs to be planes with constant slope and aspect, a major simplification given the complex surfaces of most cliffs. We develop the first grid-based model of cliff backwasting for two cliffs on debris-covered Lirung Glacier, Nepal. The model includes an improved representation of shortwave and longwave radiation, and their interplay with the glacier topography. Shortwave radiation varies considerably across the two cliffs, mostly due to direct radiation. Diffuse radiation is the major shortwave component, as the direct component is strongly reduced by the cliffs’ aspect and slope through self-shading. Incoming longwave radiation is higher than the total incoming shortwave flux, due to radiation emitted by the surrounding terrain, which is 25% of the incoming flux. Melt is highly variable in space, suggesting that simple models provide inaccurate estimates of total melt volumes. Although only representing 0.09% of the glacier tongue area, the total melt at the two cliffs over the measurement period is 2313 and 8282 m3, 1.23% of the total melt simulated by a glacio-hydrological model for the glacier’s tongue.
- Meteorological conditions, seasonal and annual mass balances of Chhota Shigri Glacier, western Himalaya, India
Mohd Farooq AZAM, Al. RAMANATHAN, Patrick WAGNON, Christian VINCENT, Anurag LINDA, Etienne BERTHIER, Parmanand SHARMA, Arindan MANDAL, Thupstan ANGCHUK, Virendra Bahadur SINGH, P.G. JOSE
- Air temperature variability in a high-elevation Himalayan catchment
Martin HEYNEN, Evan MILES, Silvan RAGETTLI, Pascal BURI, Walter W. IMMERZEEL, Francesca PELLICCIOTTI
- An assessment of basin-scale glaciological and hydrological sensitivities in the Hindu Kush–Himalaya
Joseph M. SHEA, Walter W. IMMERZEEL
The paper by Emily and Walter on the modelling of high-altitude precipitation processes in the Langtang catchment using WRF is now available online (open access):
High-altitude meteorological processes in the Himalaya are influenced by complex interactions between the topography and the monsoon and westerly circulation systems. In this study, we use the Weather Research and Forecasting model configured with high spatial resolution to understand seasonal patterns of near-surface meteorological fields and precipitation processes in the Langtang catchment in the central Himalaya. Using a unique high-altitude observational network, we evaluate a simulation from 17 June 2012 to 16 June 2013 and conclude that, at 1 km horizontal grid spacing, the model captures the main features of observed meteorological variability in the catchment. The finer representation of the complex terrain and explicit simulation of convection at this grid spacing give strong improvements in near-surface air temperature and small improvements in precipitation, in particular in themagnitudes of daytime convective precipitation and at higher elevations. The seasonal differences are noteworthy, including a reversal in the vertical and along-valley distributions of precipitation between the monsoon and winter seasons, with peak values simulated at lower altitudes (~3000m above sea level (asl)) and in the upper regions (above 5000m asl) in each season, respectively. We conclude that there is great potential for improving the local accuracy of climate change impact studies in the Himalaya by using high-resolution atmospheric models to generate the forcing for such studies.