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New study on upper Indus precipitation

Reconciling high-altitude precipitation in the upper Indus basin with glacier mass balances and runoff

Abstract

Mountain ranges in Asia are important water suppliers, especially if downstream climates are arid, water demands are high and glaciers are abundant. In such basins, the hydrological cycle depends heavily on high-altitude precipitation. Yet direct observations of high-altitude precipitation are lacking and satellite derived products are of insufficient resolution and quality to capture spatial variation and magnitude of mountain precipitation. Here we use glacier mass balances to inversely infer the high-altitude precipitation in the upper Indus basin and show that the amount of precipitation required to sustain the observed mass balances of large glacier systems is far beyond what is observed at valley stations or estimated by gridded precipitation products. An independent validation with observed river flow confirms that the water balance can indeed only be closed when the high-altitude precipitation on average is more than twice as high and in extreme cases up to a factor of 10 higher than previously thought. We conclude that these findings alter the present understanding of high-altitude hydrology and will have an important bearing on climate change impact studies, planning and design of hydropower plants and irrigation reservoirs as well as the regional geopolitical situation in general.

 

Immerzeel, W. W., Wanders, N., Lutz, A. F., Shea, J. M. and Bierkens, M. F. P., 2015, Reconciling high altitude precipitation with glacier mass balances and runoff, Hydrol. Earth Syst. Sci., 12, 4755–4784.

 

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Papers in the Annals of Glaciology

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.

Available online

  • 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
    Abstract
    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
    Abstract
    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
    Abstract
    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.

Accepted 

  • 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

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WRF Langtang paper available online

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):

  • Abstract
    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.

Lirung Glacier ice cliff energy balance modelling

The first paper on energy balance modelling of Lirung is now available online (open access):

  • Abstract
    Ice cliffs have been identified as a reason for higher ablation rates on debris-covered glaciers than are implied by the insulation effects of the debris. This study aims to improve our understanding of cliff backwasting, and the role of radiative fluxes in particular. An energy-balance model is forced with new data gathered in May and October 2013 on Lirung Glacier, Nepalese Himalaya. Observations show substantial variability in melt between cliffs, between locations on any cliff and between seasons. Using a high-resolution digital elevation model we calculate longwave fluxes incident to the cliff from surrounding terrain and include the effect of local shading on shortwave radiation. This is an advance over previous studies, that made simplified assumptions on cliff geometry and radiative fluxes. Measured melt rates varied between 3.25 and 8.6 cm d–1 in May and 0.18 and 1.34 cm d–1 in October. Model results reproduce the strong variability in space and time, suggesting considerable differences in radiative fluxes over one cliff. In October the model fails to reproduce stake readings, probably due to the lack of a refreezing component. Disregarding local topography can lead to overestimation of melt at the point scale by up to ~9%.

 

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