| publications-2651 |
Peer reviewed articles |
2016 |
Arthur F. Lutz, Herbert W. ter Maat, Hester Biemans, Arun B. Shrestha, Philippus Wester, Walter W. Immerzeel |
Selecting representative climate models for climate change impact studies: an advanced envelope-based selection approach |
International Journal of Climatology |
10.1002/joc.4608 |
Uncategorized |
Groundwater |
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ABSTRACTClimate change impact studies depend on projections of future climate provided by climate models. The number of climate models is large and increasing, yet limitations in computational capacity make it necessary to compromise the number of climate models that can be included in a climate change impact study. The selection of climate models is not straightforward and can be done by following different methods. Usually, the selection is either based on the entire range of changes in climatic variables as projected by the total ensemble of available climate models or on the skill of climate models to simulate past climate. The present study combines these approaches in a three‐step sequential climate model selection procedure: (1) initial selection of climate models based on the range of projected changes in climatic means, (2) refined selection based on the range of projected changes in climatic extremes and (3) final selection based on the climate model skill to simulate past climate. This procedure is illustrated for a study area covering the Indus, Ganges and Brahmaputra river basins. Subsequently, the changes in climate between 1971–2000 and 2071–2100 are analysed, showing that the future climate projections in this area are highly uncertain but that changes are imminent. |
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| publications-2652 |
Peer reviewed articles |
2016 |
P.D.A. Kraaijenbrink, J.M. Shea, F. Pellicciotti, S.M. de Jong, W.W. Immerzeel |
Object-based analysis of unmanned aerial vehicle imagery to map and characterise surface features on a debris-covered glacier |
Remote Sensing of Environment |
10.1016/j.rse.2016.09.013 |
Uncategorized |
River Basins |
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No abstract available |
676819 |
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| publications-2653 |
Peer reviewed articles |
2017 |
Evan S. Miles, Jakob F. Steiner, Fanny Brun |
Highly variable aerodynamic roughness length ( z 0 ) for a hummocky debris-covered glacier |
Journal of Geophysical Research: Atmospheres |
10.1002/2017JD026510 |
Uncategorized |
River Basins |
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AbstractThe aerodynamic roughness length (z0) is an essential parameter in surface energy balance studies, but few literature values exist for debris‐covered glaciers. We use microtopographic and aerodynamic methods to assess the spatial variability of z0 for Lirung Glacier, Nepal. We apply structure from motion to produce digital elevation models for three nested domains: five 1 m2 plots, a 21,300 m2 surface depression, and the lower 550,000 m2 of the debris‐mantled tongue. Wind and temperature sensor towers were installed in the vicinity of the plots within the surface depression in October 2014. We calculate z0 according to a variety of transect‐based microtopographic parameterizations for each plot, then develop a grid version of the algorithms by aggregating data from all transects. This grid approach is applied to the surface depression digital elevation model to characterize z0 spatial variability. The algorithms reproduce the same variability among transects and plots, but z0 estimates vary by an order of magnitude between algorithms. Across the study depression, results from different algorithms are strongly correlated. Using Monin‐Obukov similarity theory, we derive z0 values from the meteorological data. Using different stability criteria, we derive median values of z0 between 0.03 m and 0.05 m, but with considerable uncertainty due to the glacier's complex topography. Considering estimates from these algorithms, results suggest that z0 varies across Lirung Glacier between ∼0.005 m (gravels) to ∼0.5 m (boulders). Future efforts should assess the importance of such variable z0 values in a distributed energy balance model. |
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| publications-2654 |
Peer reviewed articles |
2017 |
Emmy E. Stigter, Niko Wanders, Tuomo M. Saloranta, Joseph M. Shea, Marc F. P. Bierkens, Walter W. Immerzeel |
Assimilation of snow cover and snow depth into a snow model to estimate snow water equivalent and snowmelt runoff in a Himalayan catchment |
The Cryosphere |
10.5194/tc-11-1647-2017 |
Data Management & Analytics |
River Basins |
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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. |
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| publications-2655 |
Peer reviewed articles |
2016 |
Pascal Buri, Evan S. Miles, Jakob F. Steiner, Walter W. Immerzeel, Patrick Wagnon, Francesca Pellicciotti |
A physically based 3-D model of ice cliff evolution over debris-covered glaciers |
Journal of Geophysical Research: Earth Surface |
10.1002/2016JF004039 |
Data Management & Analytics |
Natural Water Bodies |
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AbstractWe use high‐resolution digital elevation models (DEMs) from unmanned aerial vehicle (UAV) surveys to document the evolution of four ice cliffs on the debris‐covered tongue of Lirung Glacier, Nepal, over one ablation season. Observations show that out of four cliffs, three different patterns of evolution emerge: (i) reclining cliffs that flatten during the ablation season; (ii) stable cliffs that maintain a self‐similar geometry; and (iii) growing cliffs, expanding laterally. We use the insights from this unique data set to develop a 3‐D model of cliff backwasting and evolution that is validated against observations and an independent data set of volume losses. The model includes ablation at the cliff surface driven by energy exchange with the atmosphere, reburial of cliff cells by surrounding debris, and the effect of adjacent ponds. The cliff geometry is updated monthly to account for the modifications induced by each of those processes. Model results indicate that a major factor affecting the survival of steep cliffs is the coupling with ponded water at its base, which prevents progressive flattening and possible disappearance of a cliff. The radial growth observed at one cliff is explained by higher receipts of longwave and shortwave radiation, calculated taking into account atmospheric fluxes, shading, and the emission of longwave radiation from debris surfaces. The model is a clear step forward compared to existing static approaches that calculate atmospheric melt over an invariant cliff geometry and can be used for long‐term simulations of cliff evolution and to test existing hypotheses about cliffs' survival. |
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| publications-2656 |
Peer reviewed articles |
2017 |
EVAN S. MILES, IAN C. WILLIS, NEIL S. ARNOLD, JAKOB STEINER, FRANCESCA PELLICCIOTTI |
Spatial, seasonal and interannual variability of supraglacial ponds in the Langtang Valley of Nepal, 1999–2013 |
Journal of Glaciology |
10.1017/jog.2016.120 |
Data Management & Analytics |
Natural Water Bodies |
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ABSTRACTSupraglacial ponds play a key role in absorbing atmospheric energy and directing it to the ice of debris-covered glaciers, but the spatial and temporal distribution of these features is not well documented. We analyse 172 Landsat TM/ETM+ scenes for the period 1999–2013 to identify thawed supraglacial ponds for the debris-covered tongues of five glaciers in the Langtang Valley of Nepal. We apply an advanced atmospheric correction routine (Landcor/6S) and use band ratio and image morphological techniques to identify ponds and validate our results with 2.5 m Cartosat-1 observations. We then characterize the spatial, seasonal and interannual patterns of ponds. We find high variability in pond incidence between glaciers (May–October means of 0.08–1.69% of debris area), with ponds most frequent in zones of low surface gradient and velocity. The ponds show pronounced seasonality, appearing in the pre-monsoon as snow melts, peaking at the monsoon onset at 2% of debris-covered area, then declining in the post-monsoon as ponds drain or freeze. Ponds are highly recurrent and persistent, with 40.5% of pond locations occurring for multiple years. Rather than a trend in pond cover over the study period, we find high interannual variability for each glacier after controlling for seasonality. |
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| publications-2657 |
Peer reviewed articles |
2017 |
Koji Fujita, Hiroshi Inoue, Takeki Izumi, Satoru Yamaguchi, Ayako Sadakane, Sojiro Sunako, Kouichi Nishimura, Walter W. Immerzeel, Joseph M. Shea, Rijan B. Kayastha, Takanobu Sawagaki, David F. Breashears, Hiroshi Yagi, Akiko Sakai |
Anomalous winter-snow-amplified earthquake-induced disaster of the 2015 Langtang avalanche in Nepal |
Natural Hazards and Earth System Sciences |
10.5194/nhess-17-749-2017 |
Water Co-Governance |
River Basins |
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Abstract. 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. |
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| publications-2658 |
Peer reviewed articles |
2017 |
A. P. Dimri, W. W. Immerzeel, N. Salzmann, R. J. Thayyen |
Comparison of climatic trends and variability among glacierized environments in the Western Himalayas |
Theoretical and Applied Climatology |
10.1007/s00704-017-2265-8 |
Uncategorized |
Natural Water Bodies |
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No abstract available |
676819 |
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| publications-2659 |
Peer reviewed articles |
2017 |
P. D. A. Kraaijenbrink, M. F. P. Bierkens, A. F. Lutz, W. W. Immerzeel |
Impact of a global temperature rise of 1.5 degrees Celsius on Asia’s glaciers |
Nature |
10.1038/nature23878 |
Data Management & Analytics |
Natural Water Bodies |
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No abstract available |
676819 |
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| publications-2660 |
Peer reviewed articles |
2016 |
FANNY BRUN, PASCAL BURI, EVAN S. MILES, PATRICK WAGNON, JAKOB STEINER, ETIENNE BERTHIER, SILVAN RAGETTLI, PHILIP KRAAIJENBRINK, WALTER W. IMMERZEEL, FRANCESCA PELLICCIOTTI |
Quantifying volume loss from ice cliffs on debris-covered glaciers using high-resolution terrestrial and aerial photogrammetry |
Journal of Glaciology |
10.1017/jog.2016.54 |
Data Management & Analytics |
Natural Water Bodies |
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ABSTRACTMass losses originating from supraglacial ice cliffs at the lower tongues of debris-covered glaciers are a potentially large component of the mass balance, but have rarely been quantified. In this study, we develop a method to estimate ice cliff volume losses based on high-resolution topographic data derived from terrestrial and aerial photogrammetry. We apply our method to six cliffs monitored in May and October 2013 and 2014 using four different topographic datasets collected over the debris-covered Lirung Glacier of the Nepalese Himalayas. During the monsoon, the cliff mean backwasting rate was relatively consistent in 2013 (3.8 ± 0.3 cm w.e. d−1) and more heterogeneous among cliffs in 2014 (3.1 ± 0.7 cm w.e. d−1), and the geometric variations between cliffs are larger. Their mean backwasting rate is significantly lower in winter (October 2013–May 2014), at 1.0 ± 0.3 cm w.e. d−1. These results are consistent with estimates of cliff ablation from an energy-balance model developed in a previous study. The ice cliffs lose mass at rates six times higher than estimates of glacier-wide melt under debris, which seems to confirm that ice cliffs provide a large contribution to total glacier melt. |
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