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[CAT] Climbing the Asian Water Tower (676819)
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9 Research products, page 1 of 1

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  • Open Access English
    Authors: 
    Steiner, Jakob F.; Gurung, Tika R.; Joshi, Sharad P.; Koch, Inka; Saloranta, Tuomo; Shea, Joseph; Shrestha, Arun B.; Stigter, Emmy; Immerzeel, Walter W.; Landscape functioning, Geocomputation and Hydrology; +1 more
    Publisher: John Wiley & Sons, Inc.
    Country: Netherlands
    Project: EC | CAT (676819)

    Abstract The Langtang catchment is a high mountain, third order catchment in the Gandaki basin in the Central Himalaya (28.2°N, 85.5°E), that eventually drains into the Ganges. The catchment spans an elevation range from 1400 to 7234 m a.s.l. and approximately one quarter of the area is glacierized. Numerous research projects have been conducted in the valley during the last four decades, with a strong focus on the cryospheric components of the catchment water balance. Since 2012 multiple weather stations and discharge stations provide measurements of atmospheric and hydrologic variables. Full weather stations are used to monitor at an hourly resolution all four radiation components (incoming and outgoing shortwave and longwave radiation; SWin/out and LWin/out), air temperature, humidity, wind speed and direction, and precipitation, and cover an elevational range of 3862–5330 m a.s.l. Air temperature and precipitation are monitored along elevation gradients for investigations of the spatial variability of the high mountain meteorology. Dedicated point‐scale observations of snow cover, depth and water equivalent as well as ice loss have been carried out over multiple years and complement the observations of the water cycle. All data presented is openly available in a database and will be updated annually. Multiple years of meteorological and hydrological observations as well as the cryosphere from a high mountain catchment in the Central Himalaya are available. Data includes multiple full weather stations throughout the catchment, measuring all components of the energy balance as well as precipitation. Discharge is monitored at the outlet of the catchment.

  • Publication . Article . Other literature type . 2019
    Open Access English
    Authors: 
    Litt, M.H.V.; Shea, Joseph M.; Wagnon, Patrick; Steiner, J.F.; Koch, Inka; Stigter, E.E.; Immerzeel, W.W.; Hydrologie; Landscape functioning, Geocomputation and Hydrology;
    Publisher: Nature Publishing Group UK
    Countries: Netherlands, France
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    AbstractTemperature index (TI) models are convenient for modelling glacier ablation since they require only a few input variables and rely on simple empirical relations. The approach is generally assumed to be reliable at lower elevations (below 3500 m above sea level, a.s.l) where air temperature (Ta) relates well to the energy inputs driving melt. We question this approach in High Mountain Asia (HMA). We study in-situ meteorological drivers of glacial ablation at two sites in central Nepal, between 2013 and 2017, using data from six automatic weather stations (AWS). During the monsoon, surface melt dominates ablation processes at lower elevations (between 4950 and 5380 m a.s.l.). As net shortwave radiation (SWnet) is the main energy input at the glacier surface, albedo (α) and cloudiness play key roles while being highly variable in space and time. For these cases only, ablation can be calculated with a TI model, or with an Enhanced TI (ETI) model that includes a shortwave radiation (SW) scheme and site specific ablation factors. In the ablation zone during other seasons and during all seasons in the accumulation zone, sublimation and other wind-driven ablation processes also contribute to mass loss, and remain unresolved with TI or ETI methods.

  • Open Access English
    Authors: 
    F. Brun; F. Brun; F. Brun; P. Wagnon; P. Wagnon; E. Berthier; J. M. Shea; J. M. Shea; J. M. Shea; W. W. Immerzeel; +5 more
    Publisher: HAL CCSD
    Countries: France, France, Netherlands
    Project: EC | CAT (676819), ANR | PRESHINE (ANR-13-SENV-0005)

    Ice cliff backwasting on debris-covered glaciers is recognized as an important mass-loss process that is potentially responsible for the “debris-cover anomaly”, i.e. the fact that debris-covered and debris-free glacier tongues appear to have similar thinning rates in the Himalaya. In this study, we quantify the total contribution of ice cliff backwasting to the net ablation of the tongue of Changri Nup Glacier, Nepal, between 2015 and 2017. Detailed backwasting and surface thinning rates were obtained from terrestrial photogrammetry collected in November 2015 and 2016, unmanned air vehicle (UAV) surveys conducted in November 2015, 2016 and 2017, and Pléiades tri-stereo imagery obtained in November 2015, 2016 and 2017. UAV- and Pléiades-derived ice cliff volume loss estimates were 3 % and 7 % less than the value calculated from the reference terrestrial photogrammetry. Ice cliffs cover between 7 % and 8 % of the total map view area of the Changri Nup tongue. Yet from November 2015 to November 2016 (November 2016 to November 2017), ice cliffs contributed to 23±5 % (24±5 %) of the total ablation observed on the tongue. Ice cliffs therefore have a net ablation rate 3.1±0.6 (3.0±0.6) times higher than the average glacier tongue surface. However, on Changri Nup Glacier, ice cliffs still cannot compensate for the reduction in ablation due to debris-cover. In addition to cliff enhancement, a combination of reduced ablation and lower emergence velocities could be responsible for the debris-cover anomaly on debris-covered tongues.

  • Open Access English
    Authors: 
    Steiner, J.F.; Litt, M.H.V.; Stigter, E.E.; Shea, Joseph M.; Bierkens, M.F.P.; Immerzeel, W.W.; Hydrologie; Landscape functioning, Geocomputation and Hydrology;
    Country: Netherlands
    Project: NWO | Closing the Himalayan Wat... (26790), EC | CAT (676819)

    Surface energy balance models are common tools to estimate melt rates of debris-covered glaciers. In the Himalayas, radiative fluxes are occasionally measured, but very limited observations of turbulent fluxes on debris-covered tongues exist to date. We present measurements collected in autumn 2016 from the 26$^{th}$ of September to the 12$^{th}$ of October from an eddy correlation (EC) tower installed on the debris-covered Lirung Glacier in Nepal during the transition between monsoon and post-monsoon. Our observations suggest that surface energy losses through turbulent fluxes reduce the positive net radiative fluxes during daylight hours between 10 and 100\%, and even lead to a net negative surface energy balance after noon. During clear days, turbulent flux losses increase to over 250 W m$^{-2}$ mainly due to high sensible heat fluxes. During overcast days the latent heat flux dominates the turbulent losses and together they reach just above 100 W m$^{-2}$. Subsequently, we validate the performance of three bulk approaches in reproducing the EC observations. Large differences exist between the approaches, and accurate estimates of surface temperature, wind speed, and surface roughness are necessary for their performance to be reasonable. Moreover, the tested bulk approaches generally overestimate turbulent latent heat fluxes by a factor 3 on clear days, because the debris-covered surface dries out rapidly, while the bulk equations assume surface saturation. Improvements to bulk surface energy models should therefore include the drying process of the surface. A sensitivity analysis suggests that, in order to be useful in distributed melt models, an accurate extrapolation of wind speed, surface temperature and surface roughness in space is a prerequisite. \textcolor{red}{By applying the best performing bulk model over a complete melt period, we show that turbulent fluxes to reduce the available energy for melt at the debris surface by 17$\%$ even at very low wind speeds.} Overall, we conclude that turbulent fluxes play an essential role in the surface energy balance of debris-covered glaciers and that it is essential to include them in melt models.

  • Open Access
    Authors: 
    Emmy E. Stigter; Maxime Litt; Maxime Litt; Jakob F. Steiner; Pleun N. J. Bonekamp; Joseph M. Shea; Joseph M. Shea; Joseph M. Shea; Marc F. P. Bierkens; Marc F. P. Bierkens; +1 more
    Country: Netherlands
    Project: EC | CAT (676819)

    Snow sublimation is a loss of water from the snowpack to the atmosphere. So far, snow sublimation has remained unquantified in the Himalaya, prohibiting a full understanding of the water balance and glacier mass balance. Hence, we measured surface latent heat fluxes with an eddy covariance system on Yala Glacier (5,350 m a.s.l) in the Nepalese Himalaya to quantify the role snow sublimation plays in the water and glacier mass budget. Observations reveal that cumulative sublimation is 32 mm for a 32-day period from October to November 2016, which is high compared to observations in other regions in the world. Multiple turbulent flux parameterizations were subsequently tested against this observed sublimation. The bulk-aerodynamic method offered the best performance, and we subsequently used this method to estimate cumulative sublimation and evaporation at the location of the eddy covariance system for the 2016–2017 winter season, which is 125 and 9 mm respectively. This is equivalent to 21% of the annual snowfall. In addition, the spatial variation of total daily sublimation over Yala Glacier was simulated with the bulk-aerodynamic method for a humid and non-humid day. Required spatial fields of meteorological variables were obtained from high-resolution WRF simulations of the region in combination with field observations. The cumulative daily sublimation at the location of the eddy covariance system equals the simulated sublimation averaged over the entire glacier. Therefore, this location appears to be representative for Yala Glacier sublimation. The spatial distribution of sublimation is primarily controlled by wind speed. Close to the ridge of Yala Glacier cumulative daily sublimation is a factor 1.7 higher than at the location of the eddy covariance system, whereas it is a factor 0.8 lower at the snout of the glacier. This illustrates that the fraction of snowfall returned to the atmosphere may be much higher than 21% at wind-exposed locations. This is a considerable loss of water and illustrates the importance and need to account for sublimation in future hydrological and mass balance studies in the Himalaya.

  • Open Access
    Authors: 
    Philip Kraaijenbrink; Joseph M. Shea; Maxime Litt; Jakob F. Steiner; Désirée Treichler; Inka Koch; Walter W. Immerzeel;
    Publisher: Frontiers Media SA
    Country: Netherlands
    Project: EC | ICEMASS (320816), EC | CAT (676819)

    A layer of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya, and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier’s surface energy budget, enhancing radiation absorption, and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with −1.4 ± 1.8, 11.0 ± 5.2, and 15.3 ± 4.7◦C for the three flights (mean ± sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 ◦C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

  • Open Access English
    Authors: 
    Evan S. Miles; Jakob F. Steiner; Ian Willis; Pascal Buri; Walter W. Immerzeel; Anna Chesnokova; Francesca Pellicciotti;
    Countries: United Kingdom, United Kingdom, Switzerland, Netherlands
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    Frontiers in Earth Science, 5 ISSN:2296-6463

  • Open Access English
    Authors: 
    Stigter, Emmy E.; Wanders, Niko; Saloranta, Tuomo M.; Shea, Joseph M.; Bierkens, M.F.P.; Immerzeel, W.W.; Hydrologie; Landdegradatie en aardobservatie; Landscape functioning, Geocomputation and Hydrology;
    Country: Netherlands
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    Abstract. Snow is an important component of water storage in the Himalayas. Previous snowmelt studies in the Himalayas have predominantly relied on remotely sensed snow cover. However, snow cover data provide no direct information on the actual amount of water stored in a snowpack, i.e., the snow water equivalent (SWE). Therefore, in this study remotely sensed snow cover was combined with in situ observations and a modified version of the seNorge snow model to estimate (climate sensitivity of) SWE and snowmelt runoff in the Langtang catchment in Nepal. Snow cover data from Landsat 8 and the MOD10A2 snow cover product were validated with in situ snow cover observations provided by surface temperature and snow depth measurements resulting in classification accuracies of 85.7 and 83.1 % respectively. Optimal model parameter values were obtained through data assimilation of MOD10A2 snow maps and snow depth measurements using an ensemble Kalman filter (EnKF). Independent validations of simulated snow depth and snow cover with observations show improvement after data assimilation compared to simulations without data assimilation. The approach of modeling snow depth in a Kalman filter framework allows for data-constrained estimation of snow depth rather than snow cover alone, and this has great potential for future studies in complex terrain, especially in the Himalayas. Climate sensitivity tests with the optimized snow model revealed that snowmelt runoff increases in winter and the early melt season (December to May) and decreases during the late melt season (June to September) as a result of the earlier onset of snowmelt due to increasing temperature. At high elevation a decrease in SWE due to higher air temperature is (partly) compensated by an increase in precipitation, which emphasizes the need for accurate predictions on the changes in the spatial distribution of precipitation along with changes in temperature.

  • Open Access English
    Authors: 
    Koji Fujita; Hiroshi Inoue; Takeki Izumi; Satoru Yamaguchi; Ayako Sadakane; Sojiro Sunako; Kouichi Nishimura; Walter W. Immerzeel; Joseph M. Shea; Rijan Bhakta Kayastha; +4 more
    Country: Netherlands
    Project: EC | CAT (676819)

    Coseismic avalanches and rockfalls, as well as their simultaneous air blast and muddy flow, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, as well as sequence of the multiple events, we conducted an intensive in situ observation in October 2015. Multitemporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81 ± 1.54 × 106 and 0.84 ± 0.92 × 106 m3, respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the collapsed glacier ice could not be dominant source for the total mass. Succeeding events were multiple rockfalls which may have been triggered by aftershocks. From the initial deposit volume and the area of the upper catchment, we estimate an average snow depth of 1.82 ± 0.46 m in the source area. This is consistent with anomalously large snow depths (1.28–1.52 m) observed at a neighboring glacier (4800–5100 m a.s.l.), which accumulated over the course of four major snowfall events between October 2014 and the earthquake on 25 April 2015. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years. The anomalous winter snowfall may have amplified the disastrous effects induced by the 2015 Gorkha earthquake in Nepal.

Advanced search in
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[CAT] Climbing the Asian Water Tower (676819)
Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
9 Research products, page 1 of 1
  • Open Access English
    Authors: 
    Steiner, Jakob F.; Gurung, Tika R.; Joshi, Sharad P.; Koch, Inka; Saloranta, Tuomo; Shea, Joseph; Shrestha, Arun B.; Stigter, Emmy; Immerzeel, Walter W.; Landscape functioning, Geocomputation and Hydrology; +1 more
    Publisher: John Wiley & Sons, Inc.
    Country: Netherlands
    Project: EC | CAT (676819)

    Abstract The Langtang catchment is a high mountain, third order catchment in the Gandaki basin in the Central Himalaya (28.2°N, 85.5°E), that eventually drains into the Ganges. The catchment spans an elevation range from 1400 to 7234 m a.s.l. and approximately one quarter of the area is glacierized. Numerous research projects have been conducted in the valley during the last four decades, with a strong focus on the cryospheric components of the catchment water balance. Since 2012 multiple weather stations and discharge stations provide measurements of atmospheric and hydrologic variables. Full weather stations are used to monitor at an hourly resolution all four radiation components (incoming and outgoing shortwave and longwave radiation; SWin/out and LWin/out), air temperature, humidity, wind speed and direction, and precipitation, and cover an elevational range of 3862–5330 m a.s.l. Air temperature and precipitation are monitored along elevation gradients for investigations of the spatial variability of the high mountain meteorology. Dedicated point‐scale observations of snow cover, depth and water equivalent as well as ice loss have been carried out over multiple years and complement the observations of the water cycle. All data presented is openly available in a database and will be updated annually. Multiple years of meteorological and hydrological observations as well as the cryosphere from a high mountain catchment in the Central Himalaya are available. Data includes multiple full weather stations throughout the catchment, measuring all components of the energy balance as well as precipitation. Discharge is monitored at the outlet of the catchment.

  • Publication . Article . Other literature type . 2019
    Open Access English
    Authors: 
    Litt, M.H.V.; Shea, Joseph M.; Wagnon, Patrick; Steiner, J.F.; Koch, Inka; Stigter, E.E.; Immerzeel, W.W.; Hydrologie; Landscape functioning, Geocomputation and Hydrology;
    Publisher: Nature Publishing Group UK
    Countries: Netherlands, France
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    AbstractTemperature index (TI) models are convenient for modelling glacier ablation since they require only a few input variables and rely on simple empirical relations. The approach is generally assumed to be reliable at lower elevations (below 3500 m above sea level, a.s.l) where air temperature (Ta) relates well to the energy inputs driving melt. We question this approach in High Mountain Asia (HMA). We study in-situ meteorological drivers of glacial ablation at two sites in central Nepal, between 2013 and 2017, using data from six automatic weather stations (AWS). During the monsoon, surface melt dominates ablation processes at lower elevations (between 4950 and 5380 m a.s.l.). As net shortwave radiation (SWnet) is the main energy input at the glacier surface, albedo (α) and cloudiness play key roles while being highly variable in space and time. For these cases only, ablation can be calculated with a TI model, or with an Enhanced TI (ETI) model that includes a shortwave radiation (SW) scheme and site specific ablation factors. In the ablation zone during other seasons and during all seasons in the accumulation zone, sublimation and other wind-driven ablation processes also contribute to mass loss, and remain unresolved with TI or ETI methods.

  • Open Access English
    Authors: 
    F. Brun; F. Brun; F. Brun; P. Wagnon; P. Wagnon; E. Berthier; J. M. Shea; J. M. Shea; J. M. Shea; W. W. Immerzeel; +5 more
    Publisher: HAL CCSD
    Countries: France, France, Netherlands
    Project: EC | CAT (676819), ANR | PRESHINE (ANR-13-SENV-0005)

    Ice cliff backwasting on debris-covered glaciers is recognized as an important mass-loss process that is potentially responsible for the “debris-cover anomaly”, i.e. the fact that debris-covered and debris-free glacier tongues appear to have similar thinning rates in the Himalaya. In this study, we quantify the total contribution of ice cliff backwasting to the net ablation of the tongue of Changri Nup Glacier, Nepal, between 2015 and 2017. Detailed backwasting and surface thinning rates were obtained from terrestrial photogrammetry collected in November 2015 and 2016, unmanned air vehicle (UAV) surveys conducted in November 2015, 2016 and 2017, and Pléiades tri-stereo imagery obtained in November 2015, 2016 and 2017. UAV- and Pléiades-derived ice cliff volume loss estimates were 3 % and 7 % less than the value calculated from the reference terrestrial photogrammetry. Ice cliffs cover between 7 % and 8 % of the total map view area of the Changri Nup tongue. Yet from November 2015 to November 2016 (November 2016 to November 2017), ice cliffs contributed to 23±5 % (24±5 %) of the total ablation observed on the tongue. Ice cliffs therefore have a net ablation rate 3.1±0.6 (3.0±0.6) times higher than the average glacier tongue surface. However, on Changri Nup Glacier, ice cliffs still cannot compensate for the reduction in ablation due to debris-cover. In addition to cliff enhancement, a combination of reduced ablation and lower emergence velocities could be responsible for the debris-cover anomaly on debris-covered tongues.

  • Open Access English
    Authors: 
    Steiner, J.F.; Litt, M.H.V.; Stigter, E.E.; Shea, Joseph M.; Bierkens, M.F.P.; Immerzeel, W.W.; Hydrologie; Landscape functioning, Geocomputation and Hydrology;
    Country: Netherlands
    Project: NWO | Closing the Himalayan Wat... (26790), EC | CAT (676819)

    Surface energy balance models are common tools to estimate melt rates of debris-covered glaciers. In the Himalayas, radiative fluxes are occasionally measured, but very limited observations of turbulent fluxes on debris-covered tongues exist to date. We present measurements collected in autumn 2016 from the 26$^{th}$ of September to the 12$^{th}$ of October from an eddy correlation (EC) tower installed on the debris-covered Lirung Glacier in Nepal during the transition between monsoon and post-monsoon. Our observations suggest that surface energy losses through turbulent fluxes reduce the positive net radiative fluxes during daylight hours between 10 and 100\%, and even lead to a net negative surface energy balance after noon. During clear days, turbulent flux losses increase to over 250 W m$^{-2}$ mainly due to high sensible heat fluxes. During overcast days the latent heat flux dominates the turbulent losses and together they reach just above 100 W m$^{-2}$. Subsequently, we validate the performance of three bulk approaches in reproducing the EC observations. Large differences exist between the approaches, and accurate estimates of surface temperature, wind speed, and surface roughness are necessary for their performance to be reasonable. Moreover, the tested bulk approaches generally overestimate turbulent latent heat fluxes by a factor 3 on clear days, because the debris-covered surface dries out rapidly, while the bulk equations assume surface saturation. Improvements to bulk surface energy models should therefore include the drying process of the surface. A sensitivity analysis suggests that, in order to be useful in distributed melt models, an accurate extrapolation of wind speed, surface temperature and surface roughness in space is a prerequisite. \textcolor{red}{By applying the best performing bulk model over a complete melt period, we show that turbulent fluxes to reduce the available energy for melt at the debris surface by 17$\%$ even at very low wind speeds.} Overall, we conclude that turbulent fluxes play an essential role in the surface energy balance of debris-covered glaciers and that it is essential to include them in melt models.

  • Open Access
    Authors: 
    Emmy E. Stigter; Maxime Litt; Maxime Litt; Jakob F. Steiner; Pleun N. J. Bonekamp; Joseph M. Shea; Joseph M. Shea; Joseph M. Shea; Marc F. P. Bierkens; Marc F. P. Bierkens; +1 more
    Country: Netherlands
    Project: EC | CAT (676819)

    Snow sublimation is a loss of water from the snowpack to the atmosphere. So far, snow sublimation has remained unquantified in the Himalaya, prohibiting a full understanding of the water balance and glacier mass balance. Hence, we measured surface latent heat fluxes with an eddy covariance system on Yala Glacier (5,350 m a.s.l) in the Nepalese Himalaya to quantify the role snow sublimation plays in the water and glacier mass budget. Observations reveal that cumulative sublimation is 32 mm for a 32-day period from October to November 2016, which is high compared to observations in other regions in the world. Multiple turbulent flux parameterizations were subsequently tested against this observed sublimation. The bulk-aerodynamic method offered the best performance, and we subsequently used this method to estimate cumulative sublimation and evaporation at the location of the eddy covariance system for the 2016–2017 winter season, which is 125 and 9 mm respectively. This is equivalent to 21% of the annual snowfall. In addition, the spatial variation of total daily sublimation over Yala Glacier was simulated with the bulk-aerodynamic method for a humid and non-humid day. Required spatial fields of meteorological variables were obtained from high-resolution WRF simulations of the region in combination with field observations. The cumulative daily sublimation at the location of the eddy covariance system equals the simulated sublimation averaged over the entire glacier. Therefore, this location appears to be representative for Yala Glacier sublimation. The spatial distribution of sublimation is primarily controlled by wind speed. Close to the ridge of Yala Glacier cumulative daily sublimation is a factor 1.7 higher than at the location of the eddy covariance system, whereas it is a factor 0.8 lower at the snout of the glacier. This illustrates that the fraction of snowfall returned to the atmosphere may be much higher than 21% at wind-exposed locations. This is a considerable loss of water and illustrates the importance and need to account for sublimation in future hydrological and mass balance studies in the Himalaya.

  • Open Access
    Authors: 
    Philip Kraaijenbrink; Joseph M. Shea; Maxime Litt; Jakob F. Steiner; Désirée Treichler; Inka Koch; Walter W. Immerzeel;
    Publisher: Frontiers Media SA
    Country: Netherlands
    Project: EC | ICEMASS (320816), EC | CAT (676819)

    A layer of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya, and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier’s surface energy budget, enhancing radiation absorption, and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with −1.4 ± 1.8, 11.0 ± 5.2, and 15.3 ± 4.7◦C for the three flights (mean ± sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 ◦C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

  • Open Access English
    Authors: 
    Evan S. Miles; Jakob F. Steiner; Ian Willis; Pascal Buri; Walter W. Immerzeel; Anna Chesnokova; Francesca Pellicciotti;
    Countries: United Kingdom, United Kingdom, Switzerland, Netherlands
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    Frontiers in Earth Science, 5 ISSN:2296-6463

  • Open Access English
    Authors: 
    Stigter, Emmy E.; Wanders, Niko; Saloranta, Tuomo M.; Shea, Joseph M.; Bierkens, M.F.P.; Immerzeel, W.W.; Hydrologie; Landdegradatie en aardobservatie; Landscape functioning, Geocomputation and Hydrology;
    Country: Netherlands
    Project: EC | CAT (676819), NWO | Closing the Himalayan Wat... (26790)

    Abstract. Snow is an important component of water storage in the Himalayas. Previous snowmelt studies in the Himalayas have predominantly relied on remotely sensed snow cover. However, snow cover data provide no direct information on the actual amount of water stored in a snowpack, i.e., the snow water equivalent (SWE). Therefore, in this study remotely sensed snow cover was combined with in situ observations and a modified version of the seNorge snow model to estimate (climate sensitivity of) SWE and snowmelt runoff in the Langtang catchment in Nepal. Snow cover data from Landsat 8 and the MOD10A2 snow cover product were validated with in situ snow cover observations provided by surface temperature and snow depth measurements resulting in classification accuracies of 85.7 and 83.1 % respectively. Optimal model parameter values were obtained through data assimilation of MOD10A2 snow maps and snow depth measurements using an ensemble Kalman filter (EnKF). Independent validations of simulated snow depth and snow cover with observations show improvement after data assimilation compared to simulations without data assimilation. The approach of modeling snow depth in a Kalman filter framework allows for data-constrained estimation of snow depth rather than snow cover alone, and this has great potential for future studies in complex terrain, especially in the Himalayas. Climate sensitivity tests with the optimized snow model revealed that snowmelt runoff increases in winter and the early melt season (December to May) and decreases during the late melt season (June to September) as a result of the earlier onset of snowmelt due to increasing temperature. At high elevation a decrease in SWE due to higher air temperature is (partly) compensated by an increase in precipitation, which emphasizes the need for accurate predictions on the changes in the spatial distribution of precipitation along with changes in temperature.

  • Open Access English
    Authors: 
    Koji Fujita; Hiroshi Inoue; Takeki Izumi; Satoru Yamaguchi; Ayako Sadakane; Sojiro Sunako; Kouichi Nishimura; Walter W. Immerzeel; Joseph M. Shea; Rijan Bhakta Kayastha; +4 more
    Country: Netherlands
    Project: EC | CAT (676819)

    Coseismic avalanches and rockfalls, as well as their simultaneous air blast and muddy flow, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, as well as sequence of the multiple events, we conducted an intensive in situ observation in October 2015. Multitemporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81 ± 1.54 × 106 and 0.84 ± 0.92 × 106 m3, respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the collapsed glacier ice could not be dominant source for the total mass. Succeeding events were multiple rockfalls which may have been triggered by aftershocks. From the initial deposit volume and the area of the upper catchment, we estimate an average snow depth of 1.82 ± 0.46 m in the source area. This is consistent with anomalously large snow depths (1.28–1.52 m) observed at a neighboring glacier (4800–5100 m a.s.l.), which accumulated over the course of four major snowfall events between October 2014 and the earthquake on 25 April 2015. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years. The anomalous winter snowfall may have amplified the disastrous effects induced by the 2015 Gorkha earthquake in Nepal.