2023 |
Brun, F., King, O., Reveillet, M., Amory, C., Planchot, A., Berthier, E., et al. (2023). Everest South Col Glacier Did Not Thin During The Period 1984-2017. Cryosphere, 171(8), 3251–3268.
Abstract: The South Col Glacier Is A Small Body Of Ice And Snow (Approx. 0.2 Km(2)) Located At The Very High Elevation Of 8000Ma.S.L. (Above Sea Level) On The Southern Ridge Of Mt. Everest. A Recent Study By Potocki Et Al. (2022) Proposed That South Col Glacier Is Rapidly Losing Mass. This Is In Contradiction To Our Comparison Of Two Digital Elevation Models Derived From Aerial Photographs Taken In December 1984 And A Stereo Pleiades Satellite Acquisition From March 2017, From Which We Estimate A Mean Elevation Change Of 0.01 +/- 0.05M A(-1). To Reconcile These Results, We Investigate Some Aspects Of The Surface Energy And Mass Balance Of South Col Glacier. From Satellite Images And A Simple Model Of Snow Compaction And Erosion, We Show That Wind Erosion Has A Major Impact On The Surface Mass Balance Due To The Strong Seasonality In Precipitation And Wind And That It Cannot Be Neglected. Additionally, We Show That The Melt Amount Predicted By A Surface Energy And Mass Balance Model Is Very Sensitive To The Model Structure And Implementation. Contrary To Previous Findings, Melt Is Likely Not A Dominant Ablation Process On This Glacier, Which Remains Mostly Snow-Covered During The Monsoon.
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Jomelli, V., Wagnon, P., Swingedouw, D., Charton, J., Braucher, R., Hue, A., et al. (2023). Unraveling The Climate Control On Debris-Free Glacier Evolution In The Everest Region (Nepal, Central Himalaya) During The Holocene. Quaternary Science Reviews, .
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2022 |
Bessin, Z., Dedieu, J. P., Arnaud, Y., Wagnon, P., Brun, F., Esteves, M., et al. (2022). Processing of VEN μS Images of High Mountains: A Case Study for Cryospheric and Hydro-Climatic Applications in the Everest Region (Nepal). Remote Sensing, 141(5).
Abstract: In the Central Himalayas, glaciers and snowmelt play an important hydrological role, as they ensure the availability of surface water outside the monsoon period. To compensate for the lack of field measurements in glaciology and hydrology, high temporal and spatial resolution optical remotely sensed data are necessary. The French-Israeli VEN μS Earth observation mission has been able to complement field measurements since 2017. The aim of this paper is to evaluate the performance of different reflectance products over the Everest region for constraining the energy balance of glaciers and for cloud and snow cover mapping applied to hydrology. Firstly, the results indicate that a complete radiometric correction of slope effects such as the Gamma one (direct and diffuse illumination) provides better temporal and statistical metrics (R-2 = 0.73 and RMSE = 0.11) versus ground albedo datasets than a single cosine correction, even processed under a fine-resolution digital elevation model (DEM). Secondly, a mixed spectral-textural approach on the VEN μS images strongly improves the cloud mapping by 15% compared with a spectral mask thresholding process. These findings will improve the accuracy of snow cover mapping over the watershed areas downstream of the Everest region.
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Fugger, S., Fyffe, C. L., Fatichi, S., Miles, E., McCarthy, M., Shaw, T. E., et al. (2022). Understanding Monsoon Controls On The Energy And Mass Balance Of glaciers in the Central and Eastern Himalaya. Cryosphere, 161(5), 1631–1652.
Abstract: The Indian and East Asian summer monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature ranges, high atmospheric water content and high precipitation rates. Glacier energy- and mass-balance modelling using in situ measurements offers insights into the ways in which surface processes are shaped by climatic regimes. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Central and Eastern Himalaya to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget primarily controls the melt of cleanice glaciers, but turbulent fluxes play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux decreases during core monsoon, but the latent heat flux cools the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes causes debris-covered glacier melt rates to stay almost constant through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface and the turbulent fluxes, which intensify melt during monsoon through surface heating and condensation. Pre-monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover lowers the melt rates at high elevation. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget, while informing and motivating further glacier- and catchment-scale research using process-based models.
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Khadka, A., Wagnon, P., Brun, F., Shrestha, D., Lejeune, Y., & Arnaud, Y. (2022). Evaluation Of Era5-Land And Harv2 Reanalysis Data At High Elevation In The Upper Dudh Koshi Basin (Everest Region, Nepal). Journal Of Applied Meteorology And Climatology, 616(8), 931–954.
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Mandal, A., Angchuk, T., Azam, M., Ramanathan, A., Wagnon, P., Soheb, M., et al. (2022). An 11-Year Record Of Wintertime Snow-Surface Energy Balance And Sublimation At 4863 M A.S.L. On The Chhota Shigri Glacier Moraine (Western Himalaya, India). Cryosphere, 161(9), 3775–3799.
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2021 |
Giese, A., Arcone, S., Hawley, R., Lewis, G., & Wagnon, P. (2021). Detecting supraglacial debris thickness with GPR under suboptimal conditions. Journal Of Glaciology, 67(266), 1108–1120.
Abstract: The thickness of a supraglacial layer is critical to the magnitude and time frame of glacier melt. Field-based, short pulse, ground-penetrating radar (GPR) has successfully measured debris thickness during a glacier's melt season, when there is a strong return from the ice-debris interface, but profiling with GPR in the absence of a highly reflective ice interface has not been explored. We investigated the performance of 960 MHz signals over 2 km of transects on Changri Nup Glacier, Nepal, during the post-monsoon. We also performed laboratory experiments to interpret the field data and investigate electromagnetic wave propagation into dry rocky debris. Laboratory tests confirmed wave penetration into the glacier ice and suggest that the ice-debris interface return was missing in field data because of a weak dielectric contrast between solid ice and porous dry debris. We developed a new method to estimate debris thicknesses by applying a statistical approach to volumetric backscatter, and our backscatter-based calculated thickness retrievals gave reasonable agreement with debris depths measured manually in the field (10-40 cm). We conclude that, when melt season profiling is not an option, a remote system near 1 GHz could allow dry debris thickness to be estimated based on volumetric backscatter.
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Khadka, A., Matthews, T., Perry, L., Koch, I., Wagnon, P., Shrestha, D., et al. (2021). Weather on Mount Everest during the 2019 summer monsoon. Weather, .
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Potter, E., Orr, A., Willis, I., Bannister, D., & Wagnon, P. (2021). Meteorological impacts of a novel debris-covered glacier category in a regional climate model across a Himalayan catchment. Atmospheric Science Letters, .
Abstract: Many of the glaciers in the Nepalese Himalaya are partially covered in a layer of loose rock known as debris cover. In the Dudh Koshi River Basin, Nepal, approximately 25% of glaciers are debris-covered. Debris-covered glaciers have been shown to have a substantial impact on near-surface meteorological variables and the surface energy balance, in comparison to clean-ice glaciers. The Weather Research and Forecasting (WRF) model is often used for high-resolution weather and climate modelling, however representation of debris-covered glaciers is not included in the standard land cover and soil categories. Here we include a simple representation of thick debris-covered glaciers in the WRF model, and investigate the impact on the near-surface atmosphere over the Dudh Koshi River Basin for July 2013. Inclusion of this new category is found to improve the model representation of near-surface temperature and relative humidity, in comparison with a simulation using the default category of clean-ice glaciers, when compared to observations. The addition of the new debris-cover category in the model warms the near-surface air over the debris-covered portion of the glacier, and the wind continues further up the valley, compared to the simulation using clean-ice. This has consequent effects on water vapour and column-integrated total water path, over both the portions of the glacier with and without debris cover. Correctly simulating meteorological variables such as these is vital for accurate precipitation forecasts over glacierized regions, and therefore estimating future glacier melt and river runoff in the Himalaya. These results highlight the need for debris cover to be included in high-resolution regional climate models over debris-covered glaciers.
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Rowan, A., Nicholson, L., Quincey, D., Gibson, M., Irvine-Fynn, T., Watson, C., et al. (2021). Seasonally stable temperature gradients through supraglacial debris in the Everest region of Nepal, Central Himalaya. Journal Of Glaciology, 67(261), 170–181.
Abstract: Rock debris covers similar to 30% of glacier ablation areas in the Central Himalaya and modifies the impact of atmospheric conditions on mass balance. The thermal properties of supraglacial debris are diurnally variable but remain poorly constrained for monsoon-influenced glaciers over the timescale of the ablation season. We measured vertical debris profile temperatures at 12 sites on four glaciers in the Everest region with debris thickness ranging from 0.08 to 2.8 m. Typically, the length of the ice ablation season beneath supraglacial debris was 160 days (15 May to 22 October)-a month longer than the monsoon season. Debris temperature gradients were approximately linear (r(2) > 0.83), measured as -40 degrees C m(-1) where debris was up to 0.1 m thick, -20 degrees C m(-1) for debris 0.1-0.5 m thick, and -4 degrees C m(-1) for debris greater than 0.5 m thick. Our results demonstrate that the influence of supraglacial debris on the temperature of the underlying ice surface, and therefore melt, is stable at a seasonal timescale and can be estimated from near-surface temperature. These results have the potential to greatly improve the representation of ablation in calculations of debris-covered glacier mass balance and projections of their response to climate change.
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Wagnon, P., Brun, F., Khadka, A., Berthier, E., Shrestha, D., Vincent, C., et al. (2021). Reanalysing the 2007-19 glaciological mass-balance series of Mera Glacier, Nepal, Central Himalaya, using geodetic mass balance. Journal Of Glaciology, 67(261), 117–125.
Abstract: The 2007-19 glaciological mass-balance series of Mera Glacier in the Everest Region, East Nepal, is reanalysed using the geodetic mass balance assessed by differencing two DEMs obtained from Pleiades stereo-images acquired in November 2012 and in October 2018. The glaciological glacier-wide annual mass balance of Mera Glacier has to be systematically decreased by 0.11 m w.e. a(-1) to match the geodetic mass balance. We attribute part of the positive bias of the glaciological mass balance to an over-estimation of the accumulation above 5520 m a.s.l., likely due to a measurement network unable to capture its spatial variability. Over the period 2007-19, Mera Glacier has lost mass at a rate of -0.41 +/- 0.20 m w.e. a(-1), in general agreement with regional averages for the central Himalaya. We observe a succession of negative mass-balance years since 2013.
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2020 |
Giese, A., Boone, A., Wagnon, P., & Hawley, R. (2020). Incorporating moisture content in surface energy balance modeling of a debris-covered glacier. Cryosphere, 14(5), 1555–1577.
Abstract: Few surface energy balance models for debriscovered glaciers account for the presence of moisture in the debris, which invariably affects the debris layer's thermal properties and, in turn, the surface energy balance and subdebris melt of a debris-covered glacier. We adapted the interactions between soil, biosphere, and atmosphere (ISBA) land surface model within the SURFace EXternalisee (SURFEX) platform to represent glacier debris rather than soil (referred to hereafter as ISBA-DEB). The new ISBA-DEB model includes the varying content, transport, and state of moisture in debris with depth and through time. It robustly simulates not only the thermal evolution of the glacier-debris-snow column but also moisture transport and phase changes within the debris – and how these, in turn, affect conductive and latent heat fluxes. We discuss the key developments in the adapted ISBA-DEB and demonstrate the capabilities of the model, including how the time- and depth-varying thermal conductivity and specific heat capacity depend on evolving temperature and moisture. Sensitivity tests emphasize the importance of accurately constraining the roughness lengths and surface slope. Emissivity, in comparison to other tested parameters, has less of an effect on melt. ISBA-DEB builds on existing work to represent the energy balance of a supraglacial debris layer through time in its novel application of a land surface model to debris-covered glaciers. Comparison of measured and simulated debris temperatures suggests that ISBA-DEB includes some – but not all – processes relevant to melt under highly permeable debris. Future work, informed by further observations, should explore the importance of advection and vapor transfer in the energy balance.
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Perry, L., Matthews, T., Guy, H., Koch, I., Khadka, A., Elmore, A., et al. (2020). Precipitation Characteristics and Moisture Source Regions on Mt. Everest in the Khumbu, Nepal. One Earth, 3(5), 594–607.
Abstract: Precipitation is critical to the water towers of the Hindu Kush-Himalaya-Karakoram region, exerting an important control on glacier mass balance and the water resources for 1.65 billion people. Given that hydroclimatic extremes and water stress have emerged as key hazards in the context of climate change, Nepal's Khumbu region overlaps key vulnerabilities. Here, we investigate the region's precipitation characteristics and moisture sources through analysis of data from a new high-altitude network of automatic weather stations, which allows for a more complete understanding of the climatological precipitation data that are critical information for local communities in the Khumbu region, visitors, and downstream populations. Our findings demonstrate that the northern Bay of Bengal is potentially an important moisture source during the monsoon period (June to August) and that westerly trajectories over land predominate for precipitation events during the postmonsoon, winter, and pre-monsoon seasons.
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Perry, L., Yuter, S., Matthews, T., Wagnon, P., Khadka, A., Aryal, D., et al. (2020). Direct observations of a Mt Everest snowstorm from the world's highest surface-based radar observations. Weather, , 3854.
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2019 |
Azam, M., Wagnon, P., Vincent, C., Ramanathan, A., Kumar, N., Srivastava, S., et al. (2019). Snow and ice melt contributions in a highly glacierized catchment of Chhota Shigri Glacier (India) over the last five decades. Journal Of Hydrology, 574, 760–773.
Abstract: Glacier-wide mass balances and runoffs are reconstructed over 1969-2016 for Chhota Shigri Glacier catchment (India) applying a glacio-hydrological model. The model is forced using in-situ daily air-temperature and precipitation records from the meteorological stations at Bhuntar Observatory (1092 m a.s.l.), glacier base camp (3850 m a.s.l.) and glacier side moraine (4863 m a.s.l.). The modelled mean annual mass balance is -0.30 +/- 0.36m w.e.a(-1) (meter water equivalent per year), while the mean catchment-wide runoff is 1.56 +/- 0.23 m w.e.a(-1) over 1969-2016. Three periods are distinguished in the reconstructed mass balance and runoff series. Periods I (1969-1985) and III (2001-2016) show glacier mass wastage at rates of -0.36 and – 0.50 m w.e.a(-1), respectively, corresponding to catchment-wide runoffs of 1.51 and 1.65 m w.e.a(-1), respectively. Conversely, period II (1986-2000) exhibits steady-state conditions with average mass balances of -0.01 m w.e.a(-1), and corresponding runoff of 1.52m w.e.a(-1). The reduced ice melt (0.20m w.e.a(-1)) over period II, in agreement with steady-state conditions, is compensated by the increased snow melt (1.03 m w.e.a(-1)), providing almost similar catchment-wide runoffs for period I and II. The increased runoff after 2000 is mainly governed by increased ice melt (0.32m w.e.a(-1)) over period III. Snow accumulation in winter and summer seasons together control the glacier-wide mass balances as well as catchment-wide runoffs. Snow melt contributes the maximum to the total mean annual runoff with 63% share while glacier melt and rain contribute 17% and 20% respectively over the whole period.
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Brun, F., Wagnon, P., Berthier, E., Jomelli, V., Maharjan, S., Shrestha, F., et al. (2019). Heterogeneous Influence of Glacier Morphology on the Mass Balance Variability in High Mountain Asia. Journal Of Geophysical Research-Earth Surface, 124(6), 1331–1345.
Abstract: We investigate the control of the morphological variables on the 2000-2016 glacier-wide mass balances of 6,470 individual glaciers of High Mountain Asia. We separate the data set into 12 regions assumed to be climatically homogeneous. We find that the slope of the glacier tongue, mean glacier elevation, percentage of supraglacial debris cover, and avalanche contributing area all together explain a maximum of 48% and a minimum of 8% of the glacier-wide mass balance variability, within a given region. The best predictors of the glacier-wide mass balance are the slope of the glacier tongue and the mean glacier elevation for most regions, with the notable exception of the inner Tibetan Plateau. Glacier-wide mass balances do not differ significantly between debris-free and debris-covered glaciers in 7 of the 12 regions analyzed. Lake-terminating glaciers have more negative mass balances than the regional averages, the influence of lakes being stronger on small glaciers than on large glaciers.
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De Kok, R., Steiner, J., Litt, M., Wagnon, P., Koch, I., Azam, M., et al. (2019). Measurements, models and drivers of incoming longwave radiation in the Himalaya. International Journal Of Climatology, .
Abstract: Melting snow and glacier ice in the Himalaya forms an important source of water for people downstream. Incoming longwave radiation (LWin) is an important energy source for melt, but there are only few measurements of LWin at high elevation. For the modelling of snow and glacier melt, the LWin is therefore often represented by parameterizations that were originally developed for lower elevation environments. With LWin measurements at eight stations in three catchments in the Himalaya, with elevations between 3,980 and 6,352 m.a.s.l., we test existing LWin parameterizations. We find that these parameterizations generally underestimate the LWin, especially in wet (monsoon) conditions, where clouds are abundant and locally formed. We present a new parameterization based only on near-surface temperature and relative humidity, both of which are easy and inexpensive to measure accurately. The new parameterization performs better than the parameterizations available in literature, in some cases halving the root-mean-squared error. The new parameterization is especially improving existing parameterizations in cloudy conditions. We also show that the choice of longwave parameterization strongly affects melt calculations of snow and ice.
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Dehecq, A., Gourmelen, N., Gardner, A., Brun, F., Goldberg, D., Nienow, P., et al. (2019). Twenty-first century glacier slowdown driven by mass loss in High Mountain Asia. Nature Geoscience, 12(1), 22–+.
Abstract: Glaciers in High Mountain Asia have experienced heterogeneous rates of loss since the 1970s. Yet, the associated changes in ice flow that lead to mass redistribution and modify the glacier sensitivity to climate are poorly constrained. Here we present observations of changes in ice flow for all glaciers in High Mountain Asia over the period 2000-2017, based on one million pairs of optical satellite images. Trend analysis reveals that in 9 of the 11 surveyed regions, glaciers show sustained slowdown concomitant with ice thinning. In contrast, the stable or thickening glaciers of the Karakoram and West Kunlun regions experience slightly accelerated glacier flow. Up to 94% of the variability in velocity change between regions can be explained by changes in gravitational driving stress, which in turn is largely controlled by changes in ice thickness. We conclude that, despite the complexities of individual glacier behaviour, decadal and regional changes in ice flow are largely insensitive to changes in conditions at the bed of the glacier and can be well estimated from ice thickness change and slope alone.
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Mimeau, L., Esteves, M., Zin, I., Jacobi, H., Brun, F., Wagnon, P., et al. (2019). Quantification of different flow components in a high-altitude glacierized catchment (Dudh Koshi, Himalaya): some cryospheric-related issues. Hydrology And Earth System Sciences, 23(9), 3969–3996.
Abstract: In a context of climate change and water demand growth, understanding the origin of water flows in the Himalayas is a key issue for assessing the current and future water resource availability and planning the future uses of water in downstream regions. Two of the main issues in the hydrology of high-altitude glacierized catchments are (i) the limited representation of cryospheric processes controlling the evolution of ice and snow in distributed hydrological models and (ii) the difficulty in defining and quantifying the hydrological contributions to the river outflow. This study estimates the relative contribution of rainfall, glaciers, and snowmelt to the Khumbu River streamflow (Upper Dudh Koshi, Nepal, 146 km(2), 43% glacierized, elevation range from 4260 to 8848 ma.s.l.) as well as the seasonal, daily, and sub-daily variability during the period 2012-2015 by using the DHSVM-GDM (Distributed Hydrological Soil Vegetation Model – Glaciers Dynamics Model) physically based glacio-hydrological model. The impact of different snow and glacier parameterizations was tested by modifying the snow albedo parameterization, adding an avalanche module, adding a reduction factor for the melt of debris-covered glaciers, and adding a conceptual englacial storage. The representation of snow, glacier, and hydrological processes was evaluated using three types of data (MODIS satellite images, glacier mass balances, and in situ discharge measurements). The relative flow components were estimated using two different definitions based on the water inputs and contributing areas. The simulated hydrological contributions differ not only depending on the used models and implemented processes, but also on different definitions of the estimated flow components. In the presented case study, ice melt and snowmelt contribute each more than 40% to the annual water inputs and 69% of the annual stream flow originates from glacierized areas. The analysis of the seasonal contributions highlights that ice melt and snowmelt as well as rain contribute to monsoon flows in similar proportions and that winter outflow is mainly controlled by the release from the englacial water storage. The choice of a given parametrization for snow and glacier processes, as well as their relative parameter values, has a significant impact on the simulated water balance: for instance, the different tested parameterizations led to ice melt contributions ranging from 42% to 54 %. The sensitivity of the model to the glacier inventory was also tested, demonstrating that the uncertainty related to the glacierized surface leads to an uncertainty of 20% for the simulated ice melt component.
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2018 |
Azam, M. F., Wagnon, P., Berthier, E., Vincent, C., Fujita, K., & Kargel, J. S. (2018). Review of the status and mass changes of Himalayan-Karakoram glaciers. Journal Of Glaciology, 64(243), 61–74.
Abstract: We present a comprehensive review of the status and changes in glacier length (since the 1850s), area and mass (since the 1960s) along the Himalayan-Karakoram (HK) region and their climate-change context. A quantitative reliability classification of the field-based mass-balance series is developed. Glaciological mass balances agree better with remotely sensed balances when we make an objective, systematic exclusion of likely flawed mass-balance series. The Himalayan mean glaciological mass budget was similar to the global average until 2000, and likely less negative after 2000. Mass wastage in the Himalaya resulted in increasing debris cover, the growth of glacial lakes and possibly decreasing ice velocities. Geodetic measurements indicate nearly balanced mass budgets for Karakoram glaciers since the 1970s, consistent with the unchanged extent of supraglacial debris-cover. Himalayan glaciers seem to be sensitive to precipitation partly through the albedo feedback on the short-wave radiation balance. Melt contributions from HK glaciers should increase until 2050 and then decrease, though a wide range of present-day area and volume estimates propagates large uncertainties in the future runoff. This review reflects an increasing understanding of HK glaciers and highlights the remaining challenges.
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Brun, F., Wagnon, P., Berthier, E., Shea, J., Immerzeel, W., Kraaijenbrink, P., et al. (2018). Ice cliff contribution to the tongue-wide ablation of Changri Nup Glacier, Nepal, central Himalaya. Cryosphere, 12(11), 3439–3457.
Abstract: 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 Pleiades tri-stereo imagery obtained in November 2015, 2016 and 2017. UAV- and Pleiades-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.
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Gaillardet, J., Braud, I., Hankard, F., Anquetin, S., Bour, O., Dorfliger, N., et al. (2018). OZCAR: The French Network of Critical Zone Observatories. Vadose Zone Journal, 17(1).
Abstract: The French critical zone initiative, called OZCAR (Observatoires de la Zone Critique-Application et Recherche or Critical Zone Observatories-Application and Research) is a National Research Infrastructure (RI). OZCAR-RI is a network of instrumented sites, bringing together 21 pre-existing research observatories monitoring different compartments of the zone situated between “the rock and the sky,” the Earth's skin or critical zone (CZ), over the long term. These observatories are regionally based and have specific initial scientific questions, monitoring strategies, databases, and modeling activities. The diversity of OZCAR-RI observatories and sites is well representative of the heterogeneity of the CZ and of the scientific communities studying it. Despite this diversity, all OZCAR-RI sites share a main overarching mandate, which is to monitor, understand, and predict (“earthcast”) the fluxes of water and matter of the Earth's near surface and how they will change in response to the “new climatic regime.” The vision for OZCAR strategic development aims at designing an open infrastructure, building a national CZ community able to share a systemic representation of the CZ, and educating a new generation of scientists more apt to tackle the wicked problem of the Anthropocene. OZCAR articulates around: (i) a set of common scientific questions and cross-cutting scientific activities using the wealth of OZCAR-RI observatories, (ii) an ambitious instrumental development program, and (iii) a better interaction between data and models to integrate the different time and spatial scales. Internationally, OZCAR-RI aims at strengthening the CZ community by providing a model of organization for pre-existing observatories and by offering CZ instrumented sites. OZCAR is one of two French mirrors of the European Strategy Forum on Research Infrastructure (eLTER-ESFRI) project.
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Gibson, M., Irvine-Fynn, T., Wagnon, P., Rowan, A., Quincey, D., Homer, R., et al. (2018). Variations in near-surface debris temperature through the summer monsoon on Khumbu Glacier, Nepal Himalaya. Earth Surface Processes And Landforms, 43(13), 2698–2714.
Abstract: Debris surface temperature is a function of debris characteristics and energy fluxes at the debris surface. However, spatial and temporal variability in debris surface temperature, and the debris properties that control it, are poorly constrained. Here, near-surface debris temperature (T-s) is reported for 16 sites across the lower elevations of Khumbu Glacier, Nepal Himalaya, for the 2014 monsoon season. The debris layer at all sites was 1m thick. We confirm the occurrence of temporal and spatial variability in T-s over a 67-day period and investigate its controls. T-s was found to exhibit marked temporal fluctuations on diurnal, short-term (1-8days) and seasonal timescales. Over the study period, two distinct diurnal patterns in T-s were identified that varied in timing, daily amplitude and maximum temperature; days in the latter half of the study period (after Day of Year 176) exhibited a lower diurnal amplitude (mean = 23 degrees C) and reduced maximum temperatures. Days with lower amplitude and minimum T-s were concurrent with periods of increased seasonal variability in on-glacier air temperature and incoming shortwave radiation, with the increased frequency of these periods attributed to increasing cloud cover as the monsoon progressed. Spatial variability in T-s was manifested in variability of diurnal amplitude and maximum T-s of 7 degrees C to 47 degrees C between sites. Local slope, debris clast size and lithology were identified as the most important drivers of spatial variability in T-s, with inclusion of these three variables in the stepwise general linear models resulting in R-2 0.89 for six out of the seven sites. The complexity of surface energy fluxes and their influence on T-s highlight that assuming a simplified relationship between air temperature and debris surface temperature in glacier melt models, and a direct relationship between debris surface temperature and debris thickness for calculating supraglacial debris thickness, should be undertaken with caution. (c) 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
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Miles, E., Watson, C., Brun, F., Berthier, E., Esteves, M., Quincey, D., et al. (2018). Glacial and geomorphic effects of a supraglacial lake drainage and outburst event, Everest region, Nepal Himalaya. Cryosphere, 12(12), 3891–3905.
Abstract: A set of supraglacial ponds filled rapidly between April and July 2017 on Changri Shar Glacier in the Everest region of Nepal, coalescing into a similar to 180 000 m(2) lake before sudden and complete drainage through Changri Shar and Khumbu glaciers (15-17 July). We use PlanetScope and Pleiades satellite orthoimagery to document the system's evolution over its very short filling period and to assess the glacial and proglacial effects of the outburst flood. We also use high-resolution stereo digital elevation models (DEMs) to complete a detailed analysis of the event's glacial and geomorphic effects. Finally, we use discharge records at a stream gauge 4 km downstream to refine our interpretation of the chronology and magnitude of the outburst. We infer largely subsurface drainage through both of the glaciers located on its flow path, and efficient drainage through the lower portion of Khumbu Glacier. The drainage and subsequent outburst of 1.36 +/- 0.19 x 10(6) m(3) of impounded water had a clear geomorphic impact on glacial and proglacial topography, including deep incision and landsliding along the Changri Nup proglacial stream, the collapse of shallow englacial conduits near the Khumbu terminus and extensive, enhanced bank erosion at least as far as 11 km downstream below Khumbu Glacier. These sudden changes destroyed major trails in three locations, demonstrating the potential hazard that short-lived, relatively small glacial lakes pose.
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Vincent, C., Soruco, A., Azam, M., Basantes-Serrano, R., Jackson, M., Kjollmoen, B., et al. (2018). A Nonlinear Statistical Model for Extracting a Climatic Signal From Glacier Mass Balance Measurements. Journal Of Geophysical Research-Earth Surface, 123(9), 2228–2242.
Abstract: Understanding changes in glacier mass balances is essential for investigating climate changes. However, glacier-wide mass balances determined from geodetic observations do not provide a relevant climatic signal as they depend on the dynamic response of the glaciers. In situ point mass balance measurements provide a direct signal but show a strong spatial variability that is difficult to assess from heterogeneous in situ measurements over several decades. To address this issue, we propose a nonlinear statistical model that takes into account the spatial and temporal changes in point mass balances. To test this model, we selected four glaciers in different climatic regimes (France, Bolivia, India, and Norway) for which detailed point annual mass balance measurements were available over a large elevation range. The model extracted a robust and consistent signal for each glacier. We obtained explained variances of 87.5, 90.2, 91.3, and 75.5% on Argentiere, Zongo, Chhota Shigri, and Nigardsbreen glaciers, respectively. The standard deviations of the model residuals are close to measurement uncertainties. The model can also be used to detect measurement errors. Combined with geodetic data, this method can provide a consistent glacier-wide annual mass balance series from a heterogeneous network. This model, available to the whole community, can be used to assess the impact of climate change in different regions of the world from long-term mass balance series.
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2017 |
Brun, F., Berthier, E., Wagnon, P., Kaab, A., & Treichler, D. (2017). A spatially resolved estimate of High Mountain Asia glacier mass balances from 2000 to 2016. Nature Geoscience, 10(9), 668–+.
Abstract: High Mountain Asia hosts the largest glacier concentration outside the polar regions. These glaciers are important contributors to streamflow in one of the most populated areas of the world. Past studies have used methods that can provide only regionally averaged glacier mass balances to assess the glacier contribution to rivers and sea level rise. Here we compute the mass balance for about 92% of the glacierized area of High Mountain Asia using time series of digital elevation models derived from satellite stereo-imagery. We calculate a total mass change of -16.3 +/- 3.5 Gt yr(-1) (-0.18 +/- 0.04 m w.e. yr(-1)) between 2000 and 2016, which is less negative than most previous estimates. Region-wide mass balances vary from 4.0 +/- 1.5 Gt yr(-1) (-0.62 +/- 0.23 m w.e. yr(-1)) in Nyainqentanglha to +1.4 +/- 0.8 Gt yr(-1) (+0.14 +/- 0.08 m w.e. yr(-1)) in Kunlun, with large intra-regional variability of individual glacier mass balances (standard deviation within a region similar to 0.20m w.e. yr(-1)). Specifically, our results shed light on the Nyainqentanglha and Pamir glacier mass changes, for which contradictory estimates exist in the literature. They provide crucial information for the calibration of the models used for projecting glacier response to climatic change, as these models do not capture the pattern, magnitude and intra-regional variability of glacier changes at present.
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Litt, M., Sicart, J. E., Six, D., Wagnon, P., & Helgason, W. D. (2017). Surface-layer turbulence, energy balance and links to atmospheric circulations over a mountain glacier in the French Alps. Cryosphere, 11(2), 971–987.
Abstract: Over Saint-Sorlin Glacier in the French Alps (45 degrees N, 6.1 degrees E; similar to 3 km(2)) in summer, we study the atmospheric surface-layer dynamics, turbulent fluxes, their uncertainties and their impact on surface energy balance (SEB) melt estimates. Results are classified with regard to largescale forcing. We use high-frequency eddy-covariance data and mean air-temperature and wind-speed vertical profiles, collected in 2006 and 2009 in the glacier's atmospheric surface layer. We evaluate the turbulent fluxes with the eddycovariance (sonic) and the profile method, and random errors and parametric uncertainties are evaluated by including different stability corrections and assuming different values for surface roughness lengths. For weak synoptic forcing, local thermal effects dominate the wind circulation. On the glacier, weak katabatic flows with a wind-speed maximum at low height (2-3 m) are detected 71% of the time and are generally associated with small turbulent kinetic energy (TKE) and small net turbulent fluxes. Radiative fluxes dominate the SEB. When the large-scale forcing is strong, the wind in the valley aligns with the glacier flow, intense downslope flows are observed, no wind-speed maximum is visible below 5 m, and TKE and net turbulent fluxes are often intense. The net turbulent fluxes contribute significantly to the SEB. The surface-layer turbulence production is probably not at equilibrium with dissipation because of interactions of largescale orographic disturbances with the flow when the forcing is strong or low-frequency oscillations of the katabatic flow when the forcing is weak. In weak forcing when TKE is low, all turbulent fluxes calculation methods provide similar fluxes. In strong forcing when TKE is large, the choice of roughness lengths impacts strongly the net turbulent fluxes from the profile method fluxes and their uncertainties. However, the uncertainty on the total SEB remains too high with regard to the net observed melt to be able to recommend one turbulent flux calculation method over another.
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Sherpa, S. F., Wagnon, P., Brun, F., Berthier, E., Vincent, C., Lejeune, Y., et al. (2017). Contrasted surface mass balances of debris-free glaciers observed between the southern and the inner parts of the Everest region (2007-15). Journal Of Glaciology, 63(240), 637–651.
Abstract: Three debris-free glaciers with strongly differing annual glaciological glacier-wide mass balances (MBs) are monitored in the Everest region (central Himalaya, Nepal). The mass budget of Mera Glacier (5.1 km(2) in 2012), located in the southern part of this region, was balanced during 2007-15, whereas Pokalde (0.1 km(2) in 2011) and West Changri Nup glaciers (0.9 km(2) in 2013), similar to 30 km further north, have been losing mass rapidly with annual glacier-wide MBs of -0.69 +/- 0.28 m w.e. a(-1) (2009-15) and -1.24 +/- 0.27 m w.e. a(-1) (2010-15), respectively. An analysis of high-elevation meteorological variables reveals that these glaciers are sensitive to precipitation, and to occasional severe cyclonic storms originating from the Bay of Bengal. We observe a negative horizontal gradient of annual precipitation in south-to-north direction across the range (<= -21 mm km(-1), i.e. -2% km(-1)). This contrasted mass-balance pattern over rather short distances is related (i) to the low maximum elevation of Pokalde and West Changri Nup glaciers, resulting in years where their accumulation area ratio is reduced to zero and (ii) to a steeper vertical gradient of MB for glaciers located in the inner arid part of the range.
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2016 |
Azam, M. F., Ramanathan, A., Wagnon, P., Vincent, C., Linda, A., Berthier, E., et al. (2016). Meteorological conditions, seasonal and annual mass balances of Chhota Shigri Glacier, western Himalaya, India. Annals Of Glaciology, 57(71), 328–338.
Abstract: We present the updated glaciological mass balance (MB) of Chhota Shigri Glacier, the longest continuous annual MB record in the Hindu-Kush Karakoram Himalaya (HKH) region. Additionally, 4 years of seasonal MBs are presented and analyzed using the data acquired at an automatic weather station (AWS-M) installed in 2009 on a lateral moraine (4863ma.s.l.). The glaciological MB series since 2002 is first recalculated using an updated glacier hypsometry and then validated against geodetic MB derived from satellite stereo-imagery between 2005 (SPOT5) and 2014 (Pleiades). Chhota Shigri Glacier lost mass between 2002 and 2014 with a cumulative glaciological MB of -6.72 m w. e. corresponding to a mean annual glacier-wide MB (B-a) of -0.56m w. e. a(-1). Equilibriumline altitude (ELA(0)) for the steady-state condition is calculated as similar to 4950 m a.s.l., corresponding to an accumulation-area ratio (AAR(0)) of similar to 61%. Analysis of seasonal MBs between 2009 and 2013 with air temperature from AWS-M and precipitation from the nearest meteorological station at Bhuntar (1050 m a.s.l.) suggests that the summer monsoon is the key season driving the interannual variability of Ba for this glacier. The intensity of summer snowfall events controls the B-a evolution via controlling summer glacier-wide MB (B-s).
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Brun, F., Buri, P., Miles, E. S., Wagnon, P., Steiner, J., Berthier, E., et al. (2016). Quantifying volume loss from ice cliffs on debris-covered glaciers using high-resolution terrestrial and aerial photogrammetry. Journal Of Glaciology, 62(234), 684–695.
Abstract: Mass 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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Buri, P., Miles, E. S., Steiner, J. F., Immerzeel, W. W., Wagnon, P., & Pellicciotti, F. (2016). A physically based 3-D model of ice cliff evolution over debris-covered glaciers. Journal Of Geophysical Research-Earth Surface, 121(12), 2471–2493.
Abstract: We 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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Vincent, C., Wagnon, P., Shea, J. M., Immerzeel, W. W., Kraaijenbrink, P., Shrestha, D., et al. (2016). Reduced melt on debris-covered glaciers: investigations from Changri Nup Glacier, Nepal. Cryosphere, 10(4), 1845–1858.
Abstract: Approximately 25% of the glacierized area in the Everest region is covered by debris, yet the surface mass balance of debris-covered portions of these glaciers has not been measured directly. In this study, ground-based measurements of surface elevation and ice depth are combined with terrestrial photogrammetry, unmanned aerial vehicle (UAV) and satellite elevation models to derive the surface mass balance of the debris-covered tongue of Changri Nup Glacier, located in the Everest region. Over the debris-covered tongue, the mean elevation change between 2011 and 2015 is -0.93 m year(-1) or 0.84 m water equivalent per year (w.e.a(-1)). The mean emergence velocity over this region, estimated from the total ice flux through a cross section immediately above the debris-covered zone, is +0.37 m w.e.a(-1). The debris-covered portion of the glacier thus has an areaaveraged mass balance of -1.21 +/- 0.2 m w.e.a(-1) between 5240 and 5525 m above sea level (m a.s.l.). Surface mass balances observed on nearby debris-free glaciers suggest that the ablation is strongly reduced (by ca. 1.8 m w.e.a(-1) /by the debris cover. The insulating effect of the debris cover has a larger effect on total mass loss than the enhanced ice ablation due to supraglacial ponds and exposed ice cliffs. This finding contradicts earlier geodetic studies and should be considered for modelling the future evolution of debris-covered glaciers.
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2015 |
Brun, F., Dumont, M., Wagnon, P., Berthier, E., Azam, M. F., Shea, J. M., et al. (2015). Seasonal changes in surface albedo of Himalayan glaciers from MODIS data and links with the annual mass balance. Cryosphere, 9(1), 341–355.
Abstract: Few glaciological field data are available on glaciers in the Hindu Kush-Karakoram-Himalayan (HKH) region, and remote sensing data are thus critical for glacier studies in this region. The main objectives of this study are to document, using satellite images, the seasonal changes of surface albedo for two Himalayan glaciers, Chhota Shigri Glacier (Himachal Pradesh, India) and Mera Glacier (Everest region, Nepal), and to reconstruct the annual mass balance of these glaciers based on the albedo data. Albedo is retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) images, and evaluated using ground based measurements. At both sites, we find high coefficients of determination between annual minimum albedo averaged over the glacier (AMAAG) and glacier-wide annual mass balance (B-a) measured with the glaciological method (R-2 = 0.75). At Chhota Shigri Glacier, the relation between AMAAG found at the end of the ablation season and B-a suggests that AMAAG can be used as a proxy for the maximum snow line altitude or equilibrium line altitude (ELA) on winter-accumulation-type glaciers in the Himalayas. However, for the summer-accumulation-type Mera Glacier, our approach relied on the hypothesis that ELA information is preserved during the monsoon. At Mera Glacier, cloud obscuration and snow accumulation limits the detection of albedo during the monsoon, but snow redistribution and sublimation in the post-monsoon period allows for the calculation of AMAAG. Reconstructed B-a at Chhota Shigri Glacier agrees with mass balances previously reconstructed using a positive degree-day method. Reconstructed B-a at Mera Glacier is affected by heavy cloud cover during the monsoon, which systematically limited our ability to observe AMAAG at the end of the melting period. In addition, the relation between AMAAG and B-a is constrained over a shorter time period for Mera Glacier (6 years) than for Chhota Shigri Glacier (11 years). Thus the mass balance reconstruction is less robust for Mera Glacier than for Chhota Shigri Glacier. However our method shows promising results and may be used to reconstruct the annual mass balance of glaciers with contrasted seasonal cycles in the western part of the HKH mountain range since the early 2000s when MODIS images became available.
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Litt, M., Sicart, J. E., Helgason, W. D., & Wagnon, P. (2015). Turbulence Characteristics in the Atmospheric Surface Layer for Different Wind Regimes over the Tropical Zongo Glacier (Bolivia,16 degrees S). Boundary-Layer Meteorology, 154(3), 471–495.
Abstract: We investigate properties of the turbulent flow and sensible heat fluxes in the atmospheric surface layer of the high elevation tropical Zongo glacier ( m a.s.l., S, Bolivia) from data collected in the dry season from July to August 2007, with an eddy-covariance system and a 6-m mast for wind speed and temperature profiles. Focus is on the predominant downslope wind regime. A low-level wind-speed maximum, around a height of m, is detected in low wind conditions (37 % of the time). In strong wind conditions (39 % of the time), no wind-speed maximum is detected. Statistical and spectral analyses reveal low frequency oscillations of the horizontal wind speed that increase vertical mixing. In strong winds, wavelet analysis shows that coherent structures systematically enhance the turbulent sensible heat fluxes, accounting for 44-52 % of the flux. In contrast, in low wind conditions, the katabatic flow is perturbed by its slow oscillations or meandering motions, inducing erratic turbulent sensible heat fluxes. These motions account for 37-43 % of the flux. On tropical glaciers, the commonly used bulk aerodynamic profile method underestimates the eddy-covariance-based flux, probably because it does not account for low frequency disturbances that influence the surface flow in both wind regimes.
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Mukherji, A., Molden, D., Nepal, S., Rasul, G., & Wagnon, P. (2015). Himalayan waters at the crossroads: issues and challenges. International Journal Of Water Resources Development, 31(2), 151–160.
Abstract: The Hindu Kush Himalayas are called the water towers of Asia as they are the source of 10 major rivers and have the largest snow and ice deposits outside the two poles. Water emanating from the HKH provides food, energy and ecosystem services to up to 1.3 billion people. Climate change and socio-economic and demographic changes have put unprecedented pressure on these water resources, leading to uncertain supplies, increased demands and higher risks of extreme events like floods and droughts. The eight articles in this special issue highlight various dimensions of the Himalayan water resources by focusing on both physical and social science aspects of water management.
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Savean, M., Delclaux, F., Chevallier, P., Wagnon, P., Gonga-Saholiariliva, N., Sharma, R., et al. (2015). Water budget on the Dudh Koshi River (Nepal): Uncertainties on precipitation. Journal Of Hydrology, 531, 850–862.
Abstract: Although vital for millions of inhabitants, Himalayan water resources remain currently poorly known, mainly because of uncertainties on hydro-meteorological measurements. In this study, the authors propose a new assessment of the water budget components of the Dudh Koshi River basin (3720 km(2), Eastern Nepal), taking into account the associated uncertainties. The water budget is studied through a cross analysis of field observations with the result of a daily hydrological conceptual distributed snow model. Both observed datasets of spatialized precipitations, interpolated with a co-kriging method, and of discharge, provided by the hydrological agency of Nepal, are completed by reanalysis data (NCEP/NCAR) for air temperature and potential evapotranspiration, as well as satellite snow products (MOD10A2) giving the dynamics of the snow cover area. According to the observation, the water budget on the basin is significantly unbalanced; it is attributed to a large underestimation of precipitation, typical of high mountain areas. By contrast, the water budget simulated by the modeling approach is well balanced; it is due to an unrealistic overestimation of the glacier melt volume. A reversing method led to assess the precipitation underestimation at around 80% of the annual amount. After the correction of the daily precipitation by this ratio, the simulated fluxes of rainfall, icemelt, and snowmelt gave 63%, 29%, and 8% of the annual discharge, respectively. This basin-wide precipitation correction is likely to change in respect to topographic or geographic parameters, or in respect to seasons, but due to an insufficient knowledge of the precipitation spatial variability, this could not be investigated here, although this may significantly change the respective proportions for rain, ice or snow melt. 2015 Elsevier B.V. All rights reserved.
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Shea, J. M., Immerzeel, W. W., Wagnon, P., Vincent, C., & Bajracharya, S. (2015). Modelling glacier change in the Everest region, Nepal Himalaya. Cryosphere, 9(3), 1105–1128.
Abstract: In this study, we apply a glacier mass balance and ice redistribution model to examine the sensitivity of glaciers in the Everest region of Nepal to climate change. Highr-esolution temperature and precipitation fields derived from gridded station data, and bias-corrected with independent station observations, are used to drive the historical model from 1961 to 2007. The model is calibrated against geodetically derived estimates of net glacier mass change from 1992 to 2008, termini position of four large glaciers at the end of the calibration period, average velocities observed on selected debris-covered glaciers, and total glacierized area. We integrate field-based observations of glacier mass balance and ice thickness with remotely sensed observations of decadal glacier change to validate the model. Between 1961 and 2007, the mean modelled volume change over the Dudh Koshi basin is -6.4 +/- 1.5 km(3), a decrease of 15.6% from the original estimated ice volume in 1961. Modelled glacier area change between 1961 and 2007 is 101.0 +/- 11.4 km(2), a decrease of approximately 20% from the initial extent. The modelled glacier sensitivity to future climate change is high. Application of temperature and precipitation anomalies from warm/dry and wet/cold end-members of the CMIP5 RCP4.5 and RCP8.5 ensemble results in sustained mass loss from glaciers in the Everest region through the 21st century.
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Shea, J. M., Wagnon, P., Immerzeel, W. W., Biron, R., Brun, F., & Pellicciotti, F. (2015). A comparative high-altitude meteorological analysis from three catchments in the Nepalese Himalaya. International Journal Of Water Resources Development, 31(2), 174–200.
Abstract: Meteorological studies in high-mountain environments form the basis of our understanding of catchment hydrology and glacier accumulation and melt processes, yet high-altitude (>4000m above sea level, asl) observatories are rare. This research presents meteorological data recorded between December 2012 and November 2013 at seven stations in Nepal, ranging in elevation from 3860 to 5360m asl. Seasonal and diurnal cycles in air temperature, vapour pressure, incoming short-wave and long-wave radiation, atmospheric transmissivity, wind speed, and precipitation are compared between sites. Solar radiation strongly affects diurnal temperature and vapour pressure cycles, but local topography and valley-scale circulations alter wind speed and precipitation cycles. The observed diurnal variability in vertical temperature gradients in all seasons highlights the importance of in situ measurements for melt modelling. The monsoon signal (progressive onset and sharp end) is visible in all data-sets, and the passage of the remnants of Typhoon Phailin in mid-October 2013 provides an interesting case study on the possible effects of such storms on glaciers in the region.
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2014 |
Azam, M. F., Wagnon, P., Vincent, C., Ramanathan, A., Favier, V., Mandal, A., et al. (2014). Processes governing the mass balance of Chhota Shigri Glacier (western Himalaya, India) assessed by point-scale surface energy balance measurements. Cryosphere, 8(6), 2195–2217.
Abstract: Some recent studies revealed that Himalayan glaciers were shrinking at an accelerated rate since the beginning of the 21st century. However, the climatic causes for this shrinkage remain unclear given that surface energy balance studies are almost nonexistent in this region. In this study, a point-scale surface energy balance analysis was performed using in situ meteorological data from the ablation zone of Chhota Shigri Glacier over two separate periods (August 2012 to February 2013 and July to October 2013) in order to understand the response of mass balance to climatic variables. Energy balance numerical modelling provides quantification of the surface energy fluxes and identification of the factors affecting glacier mass balance. The model was validated by comparing the computed and observed ablation and surface temperature data. During the summer-monsoon period, net radiation was the primary component of the surface energy balance accounting for 80% of the total heat flux followed by turbulent sensible (13 %), latent (5 %) and conductive (2 %) heat fluxes. A striking feature of the energy balance is the positive turbulent latent heat flux, suggesting re-sublimation of moist air at the glacier surface, during the summer-monsoon characterized by relatively high air temperature, high relative humidity and a continual melting surface. The impact of the Indian Summer Monsoon on Chhota Shigri Glacier mass balance has also been assessed. This analysis demonstrates that the intensity of snowfall events during the summer-monsoon plays a key role on surface albedo (melting is reduced in the case of strong snowfalls covering the glacier area), and thus is among the most important drivers controlling the annual mass balance of the glacier. The summer-monsoon air temperature, controlling the precipitation phase (rain versus snow and thus albedo), counts, indirectly, also among the most important drivers.
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Azam, M. F., Wagnon, P., Vincent, C., Ramanathan, A., Linda, A., & Singh, V. B. (2014). Reconstruction of the annual mass balance of Chhota Shigri glacier, Western Himalaya, India, since 1969. Annals Of Glaciology, 55(66), 69–80.
Abstract: This study presents a reconstruction of the mass balance (MB) of Chhota Shigri glacier, Western Himalaya, India, and discusses the regional climatic drivers responsible for its evolution since 1969. The MB is reconstructed by a temperature-index and an accumulation model using daily airtemperature and precipitation records from the nearest meteorological station, at Bhuntar Observatory. The only adjusted parameter is the altitudinal precipitation gradient. The model is calibrated against 10 years of annual altitudinal MB measurements between 2002 and 2012 and decadal cumulative MBs between 1988 and 2010. Three periods were distinguished in the MB series. Periods I (1969-85) and III (2001-12) show significant mass loss at MB rates of -0.36 +/- 0.36 and -0.57 +/- 0.36 m w.e.a(-1) respectively, whereas period II (1986-2000) exhibits steady-state conditions with average MBs of -0.01 +/- 0.36 m w.e.a(-1). The comparison among these three periods suggests that winter precipitation and summer temperature are almost equally important drivers controlling the MB pattern of Chhota Shigri glacier at decadal scale. The sensitivity of the modelled glacier-wide MB to temperature is -0.52 m w.e.a(-1) degrees C-1 whereas the sensitivity to precipitation is calculated as 0.16 m w.e.a(-1) for a 10% change.
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Berthier, E., Vincent, C., Magnusson, E., Gunnlaugsson, A. T., Pitte, P., Le Meur, E., et al. (2014). Glacier topography and elevation changes derived from Pleiades sub-meter stereo images. Cryosphere, 8(6), 2275–2291.
Abstract: In response to climate change, most glaciers are losing mass and hence contribute to sea-level rise. Repeated and accurate mapping of their surface topography is required to estimate their mass balance and to extrapolate/calibrate sparse field glaciological measurements. In this study we evaluate the potential of sub-meter stereo imagery from the recently launched Pleiades satellites to derive digital elevation models (DEMs) of glaciers and their elevation changes. Our five evaluation sites, where nearly simultaneous field measurements were collected, are located in Iceland, the European Alps, the central Andes, Nepal and Antarctica. For Iceland, the Pleiades DEM is also compared to a lidar DEM. The vertical biases of the Pleiades DEMs are less than 1m if ground control points (GCPs) are used, but reach up to 7m without GCPs. Even without GCPs, vertical biases can be reduced to a few decimetres by horizontal and vertical co-registration of the DEMs to reference altimetric data on ice-free terrain. Around these biases, the vertical precision of the Pleiades DEMs is +/- 1m and even +/- 0.5m on the flat glacier tongues (1 sigma confidence level). Similar precision levels are obtained in the accumulation areas of glaciers and in Antarctica. We also demonstrate the high potential of Pleiades DEMs for measuring seasonal, annual and multi-annual elevation changes with an accuracy of 1m or better if cloud-free images are available. The negative region-wide mass balances of glaciers in the Mont-Blanc area (-1.04 +/- 0.23 ma(-1) water equivalent, w.e.) are revealed by differencing Satellite pour l'Observation de la Terre 5 (SPOT 5) and Pleiades DEMs acquired in August 2003 and 2012, confirming the accelerated glacial wastage in the European Alps.
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Gilbert, A., Gagliardini, O., Vincent, C., & Wagnon, P. (2014). A 3-D thermal regime model suitable for cold accumulation zones of polythermal mountain glaciers. Journal Of Geophysical Research-Earth Surface, 119(9), 1876–1893.
Abstract: Analysis of the thermal and mechanical response of high altitude glaciers to climate change is crucial to assess future glacier hazards associated with thermal regime changes. This paper presents a new fully thermo-mechanically coupled transient thermal regime model including enthalpy transport, firn densification, full-Stokes porous flow, free surface evolution, strain heating, surface meltwater percolation, and refreezing. The model is forced by daily air temperature data and can therefore be used to perform prognostic simulations for different future climate scenarios. The set of equations is solved using the finite element ice sheet/ice flow model Elmer/Ice. This model is applied to the Col du Dome glacier (Mont Blanc area, 4250ma.s.l., France) where a comprehensive data set is available. The results show that the model is capable of reproducing observed density and velocity fields as well as borehole temperature evolution. The strong spatial variability of englacial temperature change observed at Col du Dome is well reproduced. This spatial variability is mainly a result of the variability of the slope aspect of the glacier surface and snow accumulation. Results support the use of this model to study the influence of climate change on cold accumulation zones, in particular to estimate where and under what conditions glaciers will become temperate in the future.
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Gilbert, A., Vincent, C., Six, D., Wagnon, P., Piard, L., & Ginot, P. (2014). Modeling near-surface firn temperature in a cold accumulation zone (Col du Dome, French Alps): from a physical to a semi-parameterized approach. Cryosphere, 8(2), 689–703.
Abstract: Analysis of the thermal regime of glaciers is crucial for glacier hazard assessment, especially in the context of a changing climate. In particular, the transient thermal regime of cold accumulation zones needs to be modeled. A modeling approach has therefore been developed to determine this thermal regime using only near-surface boundary conditions coming from meteorological observations. In the first step, a surface energy balance (SEB) model accounting for water percolation and radiation penetration in firn was applied to identify the main processes that control the subsurface temperatures in cold firn. Results agree well with subsurface temperatures measured at Col du Dome (4250m above sea level (a.s.l.)), France. In the second step, a simplified model using only daily mean air temperature and potential solar radiation was developed. This model properly simulates the spatial variability of surface melting and subsurface firn temperatures and was used to accurately reconstruct the deep borehole temperature profiles measured at Col du Dome. Results show that percolation and refreezing are efficient processes for the transfer of energy from the surface to underlying layers. However, they are not responsible for any higher energy uptake at the surface, which is exclusively triggered by increasing energy flux from the atmosphere due to SEB changes when surface temperatures reach 0 degrees C. The resulting enhanced energy uptake makes cold accumulation zones very vulnerable to air temperature rise.
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Ginot, P., Dumont, M., Lim, S., Patris, N., Taupin, J. D., Wagnon, P., et al. (2014). A 10 year record of black carbon and dust from a Mera Peak ice core (Nepal): variability and potential impact on melting of Himalayan glaciers. Cryosphere, 8(4), 1479–1496.
Abstract: A shallow ice core was extracted at the summit of Mera Peak at 6376ma.s.l. in the southern flank of the Nepalese Himalaya range. From this core, we reconstructed the seasonal deposition fluxes of dust and refractory black carbon (rBC) since 1999. This archive presents well preserved seasonal cycles based on a monsoonal precipitation pattern. According to the seasonal precipitation regime in which 80% of annual precipitation falls between June and September, we estimated changes in the concentrations of these aerosols in surface snow. The analyses revealed that mass fluxes are a few orders of magnitude higher for dust (10.4 +/- 2.8 gm(-2) yr(-1)) than for rBC (7.9 +/- 2.8 mgm(-2) yr(-1)). The relative lack of seasonality in the dust record may reflect a high background level of dust inputs, whether from local or regional sources. Over the 10-year record, no deposition flux trends were detected for any of the species of interest. The data were then used to simulate changes in the surface snow albedo over time and the potential melting caused by these impurities. Mean potential melting caused by dust and rBC combined was 713 kgm(-2) yr(-1), and for rBC alone, 342 kgm(-2) yr(-1) for rBC under certain assumptions. Compared to the melting rate measured using the mass and energy balance at 5360ma.s.l. on Mera Glacier between November 2009 and October 2010, i.e. 3000 kgm(-2) yr(-1) and 3690 kgm(-2) yr(-1) respectively, the impact of rBC represents less than 16% of annual potential melting while the contribution of dust and rBC combined to surface melting represents a maximum of 26 %. Over the 10-year period, rBC variability in the ice core signal primarily reflected variability of the monsoon signal rather than variations in the intensity of emissions.
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Menegoz, M., Krinner, G., Balkanski, Y., Boucher, O., Cozic, A., Lim, S., et al. (2014). Snow cover sensitivity to black carbon deposition in the Himalayas: from atmospheric and ice core measurements to regional climate simulations. Atmospheric Chemistry And Physics, 14(8), 4237–4249.
Abstract: We applied a climate-chemistry global model to evaluate the impact of black carbon (BC) deposition on the Himalayan snow cover from 1998 to 2008. Using a stretched grid with a resolution of 50 km over this complex topography, the model reproduces reasonably well the remotely sensed observations of the snow cover duration. Similar to observations, modelled atmospheric BC concentrations in the central Himalayas reach a minimum during the monsoon and a maximum during the post-and pre-monsoon periods. Comparing the simulated BC concentrations in the snow with observations is more challenging because of their high spatial variability and complex vertical distribution. We simulated spring BC concentrations in surface snow varying from tens to hundreds of μg kg(-1), higher by one to two orders of magnitude than those observed in ice cores extracted from central Himalayan glaciers at high elevations (>6000ma.s.l.), but typical for seasonal snow cover sampled in middle elevation regions (<6000ma.s.l.). In these areas, we estimate that both wet and dry BC depositions affect the Himalayan snow cover reducing its annual duration by 1 to 8 days. In our simulations, the effect of anthropogenic BC deposition on snow is quite low over the Tibetan Plateau because this area is only sparsely snow covered. However, the impact becomes larger along the entire Hindu-Kush, Karakorum and Himalayan mountain ranges. In these regions, BC in snow induces an increase of the net short-wave radiation at the surface with an annual mean of 1 to 3Wm(-2) leading to a localised warming between 0.05 and 0.3 degrees C.
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2013 |
Lejeune, Y., Bertrand, J. M., Wagnon, P., & Morin, S. (2013). A physically based model of the year-round surface energy and mass balance of debris-covered glaciers. Journal Of Glaciology, 59(214), 327–344.
Abstract: Debris-covered glaciers respond to atmospheric conditions in different ways from debris-free glaciers, due to the presence of debris at the surface during the ablation season and at the snow/ice interface during the accumulation season. Understanding the response of debris-covered glaciers to a variety of meteorological conditions in a physically sound manner is essential to quantify meltwater discharge and to predict their response to climate change. To tackle this issue, we developed the Crocus-DEB model as an adaptation of the detailed snowpack model Crocus, to simulate the energy and mass balance of debris-covered glaciers, including periods when debris is covered by snow. Crocus-DEB was evaluated with data gathered during a field experiment using artificial debris covering the snowpack at Col de Porte, France, with very good results in terms of conductive heat flux, both at the surface and at the interface between the debris and the underlying dense snow taken as a surrogate for ice, with and without snow overlying the debris. The model was also evaluated using field data from the debris-covered glacier Changri Nup, Nepal, Himalaya. This paper introduces the design of the model, its performance and its ability to explore relationships between model parameters, meteorological conditions and the critical debris thickness.
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Rabatel, A., Francou, B., Soruco, A., Gomez, J., Caceres, B., Ceballos, J. L., et al. (2013). Current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change. Cryosphere, 7(1), 81–102.
Abstract: The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age (LIA, mid-17th-early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the one computed on a global scale. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from -0.2mw. e. in the period 1964-1975 to -0.76mw. e. in the period 1976-2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia show that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance at the decadal timescale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10 degrees C decade(-1) in the last 70 yr. The higher frequency of El Nino events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world.
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Vincent, C., Ramanathan, A., Wagnon, P., Dobhal, D. P., Linda, A., Berthier, E., et al. (2013). Balanced conditions or slight mass gain of glaciers in the Lahaul and Spiti region (northern India, Himalaya) during the nineties preceded recent mass loss. Cryosphere, 7(2), 569–582.
Abstract: The volume change of the Chhota Shigri Glacier (India, 32 degrees 20 N, 77 degrees 30' E) between 1988 and 2010 has been determined using in situ geodetic measurements. This glacier has experienced only a slight mass loss between 1988 and 2010 (-3.8 +/- 2.0mw.e. (water equivalent) corresponding to -0.17 pm 0.09mw.e. yr(-1)). Using satellite digital elevation models (DEM) differencing and field measurements, we measure a negative mass balance (MB) between 1999 and 2010 (-4.8 +/- 1.8mw.e. corresponding to -0.44 +/- 0.16mw.e. yr(-1)). Thus, we deduce a slightly positive or near-zero MB between 1988 and 1999 (+1.0 +/- 2.7mw.e. corresponding to +0.09 +/- 0.24mw.e. yr(-1)). Furthermore, satellite DEM differencing reveals that the MB of the Chhota Shigri Glacier (-0.39 pm 0.15mw.e. yr(-1)) has been only slightly less negative than the MB of a 2110 km(2) glaciarized area in the Lahaul and Spiti region (-0.44 +/- 0.09mw.e. yr(-1)) during 1999-2011. Hence, we conclude that the ice wastage is probably moderate in this region over the last 22 yr, with near equilibrium conditions during the nineties, and an ice mass loss after. The turning point from balanced to negative mass budget is not known but lies probably in the late nineties and at the latest in 1999. This positive or near-zero MB for Chhota Shigri Glacier (and probably for the surrounding glaciers of the Lahaul and Spiti region) during at least part of the 1990s contrasts with a recent compilation of MB data in the Himalayan range that indicated ice wastage since 1975. However, in agreement with this compilation, we confirm more negative balances since the beginning of the 21st century.
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Wagnon, P., Vincent, C., Arnaud, Y., Berthier, E., Vuillermoz, E., Gruber, S., et al. (2013). Seasonal and annual mass balances of Mera and Pokalde glaciers (Nepal Himalaya) since 2007. Cryosphere, 7(6), 1769–1786.
Abstract: In the Everest region, Nepal, ground-based monitoring programmes were started on the debris-free Mera Glacier (27.7 degrees N, 86.9 degrees E; 5.1 km(2), 6420 to 4940 m a.s.l.) in 2007 and on the small Pokalde Glacier (27.9 degrees N, 86.8 degrees E; 0.1 km(2), 5690 to 5430 m a.s.l., similar to 25 km north of Mera Glacier) in 2009. These glaciers lie on the southern flank of the central Himalaya under the direct influence of the Indian monsoon and receive more than 80% of their annual precipitation in summer (June to September). Despite a large inter-annual variability with glacier-wide mass balances ranging from -0.67 +/- 0.28 m w.e. in 2011-2012 (Equilibrium-line altitude (ELA) at similar to 5800 m a.s.l.) to +0.46 +/- 0.28 m w.e. in 2010-2011 (ELA at similar to 5340 m a.s.l.), Mera Glacier has been shrinking at a moderate mass balance rate of -0.08 +/- 0.28 m w.e. yr(-1) since 2007. Ice fluxes measured at two distinct transverse cross sections at similar to 5350 m a.s.l. and similar to 5520 m a.s.l. confirm that the mean state of this glacier over the last one or two decades corresponds to a limited mass loss, in agreement with remotely-sensed region-wide mass balances of the Everest area. Seasonal mass balance measurements show that ablation and accumulation are concomitant in summer which in turn is the key season controlling the annual glacier-wide mass balance. Unexpectedly, ablation occurs at all elevations in winter due to wind erosion and sublimation, with remobilised snow potentially being sublimated in the atmosphere. Between 2009 and 2012, the small Pokalde Glacier lost mass more rapidly than Mera Glacier with respective mean glacier-wide mass balances of -0.72 and -0.23 +/- 0.28 m w.e. yr(-1). Low-elevation glaciers, such as Pokalde Glacier, have been usually preferred for in-situ observations in Nepal and more generally in the Himalayas, which may explain why compilations of ground-based mass balances are biased toward negative values compared with the regional mean under the present-day climate.
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2012 |
Azam, M. F., Wagnon, P., Ramanathan, A., Vinicent, C., Sharma, P., Arnaud, Y., et al. (2012). From balance to imbalance: a shift in the dynamic behaviour of Chhota Shigri glacier, western Himalaya, India. Journal Of Glaciology, 58(208), 315–324.
Abstract: Mass-balance and dynamic behaviour of Chhota Shigri glacier, western Himalaya, India, has been investigated between 2002 and 2010 and compared to data collected in 1987-89. During the period 2002-10, the glacier experienced a negative glacier-wide mass balance of -0.67 +/- 0.40 m w.e.a(-1). Between 2003 and 2010, elevation and ice-flow velocities slowly decreased in the ablation area, leading to a 24-37% reduction in ice fluxes, an expected response of the glacier dynamics to its recent negative mass balances. The reduced ice fluxes are still far larger than the balance fluxes calculated from the 2002-10 average surface mass balances. Therefore, further slowdown, thinning and terminus retreat of Chhota Shigri glacier are expected over the next few years. Conversely, the 2003/04 ice fluxes are in good agreement with ice fluxes calculated assuming that the glacier-wide mass balance is zero. Given the limited velocity change between 1987-89 and 2003/04 and the small terminus change between 1988 and 2010, we suggest that the glacier has experienced a period of near-zero or slightly positive mass balance in the 1990s, before shifting to a strong imbalance in the 21st century. This result challenges the generally accepted idea that glaciers in the Western Himalaya have been shrinking rapidly for the last few decades.
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Gilbert, A., Vincent, C., Wagnon, P., Thibert, E., & Rabatel, A. (2012). The influence of snow cover thickness on the thermal regime of Tete Rousse Glacier (Mont Blanc range, 3200 m a.s.l.): Consequences for outburst flood hazards and glacier response to climate change. Journal Of Geophysical Research-Earth Surface, 117, F04018.
Abstract: Tete Rousse Glacier (French Alps) was responsible for an outburst flood in 1892 that devastated the village of St Gervais-Le Fayet close to Chamonix, causing 175 fatalities. Changes in the hydrothermal configuration of the glacier are suspected to be the cause of this catastrophic outburst flood. In 2010, geophysical surveys of this glacier revealed a subglacial lake that was subsequently drained artificially. The processes controlling the thermal regime of the glacier have been investigated on the basis of measurements and snow/firn cover and heat flow models using meteorological data covering the last 200 years. Temperature measurements show a polythermal structure with subglacial water trapped by the cold lowest part of the glacier (-2 degrees C). The modeling approach shows that the polythermal structure is due to temporal changes in the depth of the snow/firn cover at the glacier surface. Paradoxically, periods with negative mass balances, associated with warmer air temperature, tend to cool the glacier, whereas years with colder temperatures, associated with positive mass balances, tend to increase the glacier temperature by increasing the firnpack depth and extent. The thermal effect of the subglacial lake is evaluated and shows that the lake was formed around 1980. According to future climate scenarios, modeling shows that the glacier may cool again in the future. This study provides insights into the thermal processes responsible for water storage inside a small almost static glacier, which can lead to catastrophic outburst floods such as the 1892 event or potentially dangerous situations as in 2010.
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Gilbert, A., Vincent, C., Wagnon, P., Thibert, E., & Rabatel, A. (2012). The influence of snow cover thickness on the thermal regime of Tete Rousse Glacier (Mont Blanc range, 3200 m a.s.l.): Consequences for outburst flood hazards and glacier response to climate change. Journal Of Geophysical Research-Earth Surface, 117.
Abstract: Tete Rousse Glacier (French Alps) was responsible for an outburst flood in 1892 that devastated the village of St Gervais-Le Fayet close to Chamonix, causing 175 fatalities. Changes in the hydrothermal configuration of the glacier are suspected to be the cause of this catastrophic outburst flood. In 2010, geophysical surveys of this glacier revealed a subglacial lake that was subsequently drained artificially. The processes controlling the thermal regime of the glacier have been investigated on the basis of measurements and snow/firn cover and heat flow models using meteorological data covering the last 200 years. Temperature measurements show a polythermal structure with subglacial water trapped by the cold lowest part of the glacier (-2 degrees C). The modeling approach shows that the polythermal structure is due to temporal changes in the depth of the snow/firn cover at the glacier surface. Paradoxically, periods with negative mass balances, associated with warmer air temperature, tend to cool the glacier, whereas years with colder temperatures, associated with positive mass balances, tend to increase the glacier temperature by increasing the firnpack depth and extent. The thermal effect of the subglacial lake is evaluated and shows that the lake was formed around 1980. According to future climate scenarios, modeling shows that the glacier may cool again in the future. This study provides insights into the thermal processes responsible for water storage inside a small almost static glacier, which can lead to catastrophic outburst floods such as the 1892 event or potentially dangerous situations as in 2010.
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Hingray, B., Dedieu, J. P., Lebel, T., Obled, C., Sicart, J. E., Six, D., et al. (2012). Glaciological and hydrometeorological observations in mountainous areas: Some current issues and perspectives. Houille Blanche-Revue Internationale De L Eau, (2), 5–11.
Abstract: Hydrometeorological observations are the basic material for a number of scientific and operational issues. They are required for studies aiming at understanding and/or modeling climate-environment-society interactions along with their spatial and temporal variations. They constitute also the basic information for estimating hydrological resources and risks, for their real time management or for prospective studies that aim to foresee adaptations strategies required by societies to face changes in resource and risks induced by ongoing global change. In mountainous areas, such observations are even more important as hydrometeorological events are more pronounced and variable than anywhere else. Here, the interest of hydrometeorological observations systems such as GLACIOCLIM in these regions is highlighted for various key hydrological issues, taken from the operational, research or environmental monitoring domains. Several observatories or measurement networks developed to meet corresponding objectives are presented. Limits of observations, associated to the measurement itself, to their spatial representativeness, to their temporal coverage and permanence are discussed. Some perspectives for improving current observations systems are finally suggested.
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2011 |
Jomelli, V., Khodri, M., Favier, V., Brunstein, D., Ledru, M. P., Wagnon, P., et al. (2011). Irregular tropical glacier retreat over the Holocene epoch driven by progressive warming. Nature, 474(7350), 196–199.
Abstract: The causes and timing of tropical glacier fluctuations during the Holocene epoch (10,000 years ago to present) are poorly understood. Yet constraining their sensitivity to changes in climate(1) is important, as these glaciers are both sensitive indicators of climate change and serve as water reservoirs for highland regions(2). Studies have so far documented extra-tropical glacier fluctuations(3,4), but in the tropics, glacier-climate relationships are insufficiently understood. Here we present a Be-10 chronology for the past 11,000 years (11 kyr), using 57 moraines from the Bolivian Telata glacier (in the Cordillera Real mountain range). This chronology indicates that Telata glacier retreated irregularly. Arapid and strong melting from the maximum extent occurred from 10.8 +/- 0.9 to 8.5 +/- 0.4 kyr ago, followed by a slower retreat until the Little Ice Age, about 200 years ago. A dramatic increase in the rate of retreat occurred over the twentieth century. A glacier-climate model indicates that, relative to modern climate, annual mean temperature for the Telata glacier region was -3.3 +/- 0.8 degrees C cooler at 11 kyr ago and remained -2.1 +/- 0.8 degrees C cooler until the end of the Little Ice Age. We suggest that long-term warming of the eastern tropical Pacific and increased atmospheric temperature in response to enhanced austral summer insolation were the main drivers for the long-term Holocene retreat of glaciers in the southern tropics.
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2010 |
Gilbert, A., Wagnon, P., Vincent, C., Ginot, P., & Funk, M. (2010). Atmospheric warming at a high-elevation tropical site revealed by englacial temperatures at Illimani, Bolivia (6340 m above sea level, 16 degrees S, 67 degrees W). J. Geophys. Res.-Atmos., 115, D10109.
Abstract: In June 1999, a deep (138.7 m) ice core was extracted from the summit glacier of Illimani, Bolivia (6340 m above sea level, 16 degrees 39'S, 67 degrees 47'W), and an englacial temperature profile was measured in the borehole. Using on-site and regional meteorological data as well as ice core stratigraphy, past surface temperatures were reconstructed with a heat flow model. The englacial temperature measurements exhibit a profile that is far from a steady state, reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions. Englacial temperature interpretation, using air temperature data, borehole temperature inversion, and melting rate quantification based on ice core density, shows two warming phases from 1900 to 1960 (+0.5 +/- 0.3 K starting approximately in 1920-1930) and from 1985 to 1999 (+0.6 +/- 0.2 K), corresponding to a mean atmospheric temperature rise of 1.1 +/- 0.2 K over the 20th century. According to various climate change scenarios, the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high-elevation site on the Illimani summit glacier could become temperate in the future. Results show that this glacier might remain cold for more than 90 years in the case of a +2 K rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches +5 K.
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Gilbert, A., Wagnon, P., Vincent, C., Ginot, P., & Funk, M. (2010). Atmospheric warming at a high-elevation tropical site revealed by englacial temperatures at Illimani, Bolivia (6340 m above sea level, 16 degrees S, 67 degrees W). Journal Of Geophysical Research-Atmospheres, 115.
Abstract: In June 1999, a deep (138.7 m) ice core was extracted from the summit glacier of Illimani, Bolivia (6340 m above sea level, 16 degrees 39'S, 67 degrees 47'W), and an englacial temperature profile was measured in the borehole. Using on-site and regional meteorological data as well as ice core stratigraphy, past surface temperatures were reconstructed with a heat flow model. The englacial temperature measurements exhibit a profile that is far from a steady state, reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions. Englacial temperature interpretation, using air temperature data, borehole temperature inversion, and melting rate quantification based on ice core density, shows two warming phases from 1900 to 1960 (+0.5 +/- 0.3 K starting approximately in 1920-1930) and from 1985 to 1999 (+0.6 +/- 0.2 K), corresponding to a mean atmospheric temperature rise of 1.1 +/- 0.2 K over the 20th century. According to various climate change scenarios, the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high-elevation site on the Illimani summit glacier could become temperate in the future. Results show that this glacier might remain cold for more than 90 years in the case of a +2 K rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches +5 K.
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Wagnon, P. (2010). Relation Climat – Glaciers en zone tropicale : études de cas dans les Andes et perspectives en Himalaya. Habilitation thesis, Université Joseph Fourier, Grenoble, .
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2009 |
Gascoin, S., Ducharne, A., Ribstein, P., Lejeune, Y., & Wagnon, P. (2009). Dependence of bare soil albedo on soil moisture on the moraine of the Zongo glacier (Bolivia): Implications for land surface modeling. J. Geophys. Res.-Atmos., 114, 11 pp.
Abstract: Although the dependence of bare soil albedo on soil moisture is a familiar observation, it is not commonly represented in climate modeling. We investigate the impact of this dependence in a land surface model using meteorological data collected on the moraine of a Bolivian glacier. The relationship which is implemented to simulate albedo variations with soil moisture is deduced from a previous field study. The model is set up at the scale of the meteorological station plot to have the most accurate control on the model calibration and validation. A snow parameter is modified to account for the fact that the model was designed for larger cell sizes. Water content measurements are used to calibrate the parameter controlling the vertical water fluxes within the soil surface layer. This allows us to enhance the model's ability to capture the fast changes in surface soil moisture. The comparison of simulated ground heat flux and outgoing longwave radiations with observations shows that the model performs well despite the fact that all other parameters are set a priori on the basis of local properties of the surface. The results show that the dependence of bare soil albedo on soil moisture, which causes an increase in the net radiation, importantly influences the turbulent fluxes at the annual and monthly time scales. The mean annual evaporation is increased by 12%. As a consequence, this parameterization modifies the computed runoff, which is reduced by more than 5% during the rainy season.
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Gascoin, S., Ducharne, A., Ribstein, P., Perroy, E., & Wagnon, P. (2009). Sensitivity of bare soil albedo to surface soil moisture on the moraine of the Zongo glacier (Bolivia). Geophys. Res. Lett., 36, 5 pp.
Abstract: The dependence of bare soil albedo on soil water content is investigated using in situ data collected on the moraine of an Andean glacier (Bolivia). This study demonstrates a high negative correlation between the two variables that is best approximated by an exponential function, in agreement with previous studies. More importantly, the average snow-free albedo value during the rainy season is 40% lower than during the dry season (0.16 vs. 0.26). These results are relevant for climate and land surface modeling applications, where bare soil albedo is often considered as a constant parameter. Citation: Gascoin, S., A. Ducharne, P. Ribstein, E. Perroy, and P. Wagnon (2009), Sensitivity of bare soil albedo to surface soil moisture on the moraine of the Zongo glacier (Bolivia), Geophys. Res. Lett., 36, L02405, doi:10.1029/2008GL036377.
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Six, D., Wagnon, P., Sicart, J. E., & Vincent, C. (2009). Meteorological controls on snow and ice ablation for two contrasting months on Glacier de Saint-Sorlin, France. Ann. Glaciol., 50(50), 66–72.
Abstract: The influence of meteorological variables on snow/ice melting has been analyzed for two very contrasting months, in summer 2006, on Glacier de Saint-Sorlin, French Alps. July 2006 was the warmest July since 1950, and August 2006 was the coldest August since 1979. The total energy available for melting was just over half as much in August as in July, due to a sharp decrease in net shortwave radiation and in turbulent flux. This decrease of net shortwave radiation was mainly controlled by a strong increase in albedo responsible for an increase of reflected shortwave radiation, as well as by a reduction in incident shortwave radiation. During the two months, net longwave radiation remained almost unchanged. The mass balance computed from energy-balance modelling or with a degree-day approach was in good agreement with measured mass balance. Differences were attributed to space and time surface aspect variations which mainly controlled the observed mass balance.
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Soruco, A., Vincent, C., Francou, B., Ribstein, P., Berger, T., Sicart, J. E., et al. (2009). Mass balance of Glaciar Zongo, Bolivia, between 1956 and 2006, using glaciological, hydrological and geodetic methods. Ann. Glaciol., 50(50), 1–8.
Abstract: The longest continuous glaciological mass-balance time-series in the intertropical zone of South America goes back to 1991 on Glaciar Zongo, Bolivia. Photogrammetric and hydrological data have been used to (1) check the specific net balance over long periods and (2) extend the mass-balance time series over the last 50 years. These data reveal a bias in the glaciological mass balance which can be explained by the field-measurement sampling network. Our study shows a large temporal variability of the surface mass balances in the ablation area and reveals strong relationships between independent surface mass-balance data coming from selected ablation areas with numerous data. It demonstrates the very large contribution (80%) of low-elevation ranges (one-third of the surface) to the specific mass balance and, consequently, the importance of the reduction of the area of the tongue. With these new results, Glaciar Zongo offers the longest and most accurate mass-balance series in any Andean country. The dataset shows that Glaciar Zongo experienced a relatively steady state over the period 1956-75, with even a slight mass gain over 1963-75, and a rapid and continuous decrease since then.
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Wagnon, P., Lafaysse, M., Lejeune, Y., Maisincho, L., Rojas, M., & Chazarin, J. P. (2009). Understanding and modeling the physical processes that govern the melting of snow cover in a tropical mountain environment in Ecuador. Journal Of Geophysical Research-Atmospheres, 114.
Abstract: The ISBA/CROCUS coupled ground-snow model developed for the Alps and subsequently adapted to the outer tropical conditions of Bolivia has been applied to a full set of meteorological data recorded at 4860 m above sea level on a moraine area in Ecuador (Antizana 15 glacier, 0 degrees 28'S; 78 degrees 09'W) between 16 June 2005 and 30 June 2006 to determine the physical processes involved in the melting and disappearance of transient snow cover in nonglaciated areas of the inner tropics. Although less accurate than in Bolivia, the model is still able to simulate snow behavior over nonglaciated natural surfaces, as long as the modeled turbulent fluxes over bare ground are reduced and a suitable function is included to represent the partitioning of the surface between bare soil and snow cover. The main difference between the two tropical sites is the wind velocity, which is more than 3 times higher at the Antizana site than at the Bolivian site, leading to a nonuniform spatial distribution of snow over nonglaciated areas that is hard to describe with a simple snow partitioning function. Net solar radiation dominates the surface energy balance and is responsible for the energy stored in snow-free areas (albedo = 0.05) and transferred horizontally to adjacent snow patches by conduction within the upper soil layers and by turbulent advection. These processes can prevent the snow cover from lasting more than a few hours or a few days. Sporadically, and at any time of the year, this inner tropical site, much wetter than the outer tropics, experiences heavy snowfalls, covering all the moraine area, and thus limiting horizontal transfers and inducing a significant time lag between precipitation events and runoff.
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Winkler, M., Juen, I., Molg, T., Wagnon, P., Gomez, J., & Kaser, G. (2009). Measured and modelled sublimation on the tropical Glaciar Artesonraju, Peru. Cryosphere, 3(1), 21–30.
Abstract: Sublimation plays a decisive role in the surface energy and mass balance of tropical glaciers. During the dry season (May-September) low specific humidity and high surface roughness favour the direct transition from ice to vapour and drastically reduce the energy available for melting. However, field measurements are scarce and little is known about the performance of sublimation parameterisations in glacier mass balance and runoff models. During 15 days in August 2005 sublimation was measured on the tongue of Glaciar Artesonraju (8 degrees 58' S, 77 degrees 38'W) in the Cordillera Blanca, Peru, using simple lysimeters. Indicating a strong dependence on surface roughness, daily totals of sublimation range from 1-3 kg m(-2) for smooth to 25 kg m(-2) for rough conditions. (The 15-day means at that time of wind speed and specific humidity were 4.3m s(-1) and 3.8 g kg(-1), respectively.) Measured sublimation was related to characteristic surface roughness lengths for momentum (z(m)) and for the scalar quantities of temperature and water vapour (z(s)), using a process-based mass balance model. Input data were provided by automatic weather stations, situated on the glacier tongue at 4750 m a.s.l. and 4810m a.s.l., respectively. Under smooth conditions the combination z(m)=2.0 mm and z(s)=1.0 mm appeared to be most appropriate, for rough conditions z(m)=20.0 mm and z(s)=10.0mm fitted best. Extending the sublimation record from April 2004 to December 2005 with the process-based model confirms, that sublimation shows a clear seasonality. 60-90% of the energy available for ablation is consumed by sublimation in the dry season, but only 10-15% in the wet season (October-April). The findings are finally used to evaluate the parameterisation of sublimation in the lower-complexity mass balance model ITGG, which has the advantage of requiring precipitation and air temperature as only input data. It turns out that the implementation of mean wind speed is a possible improvement for the representation of sublimation in the ITGG model.
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2008 |
Favier, V., Coudrain, A., Cadier, E., Francou, B., Ayabaca, E., Maisincho, L., et al. (2008). Evidence of groundwater flow on Antizana ice-covered volcano, Ecuador. Hydrol. Sci. J.-J. Sci. Hydrol., 53(1), 278–291.
Abstract: Hydrological and glaciological data were gathered in the watershed (1.37 km(2)) of the Antizana Glacier 15 (0.7 km(2)) in the periods 1997-2002 and 1995-2005, respectively. In addition, tracer experiments were carried out to analyse the flow through permeable morainic deposits located between the glacier snout and the runoff gauging station. Over 11 years, the mean specific net balance of the glacier was negative (-627 mm w.e.), despite the occurrence of positive values in the La Nina years (1999-2000). From the glacier net mass balance between 1997 and 2002, it was found that the mean flow originating from ice melt was significantly higher than the mean discharge measured at the hydrological station. Analyses of tracer experiments and of the different components of the hydrological balance suggest groundwater flow that originates below the glacier accounts for the remaining water. This result is important for regional analyses of available water resources and for the relationship between hydro-cryospheric processes and volcanic activity.
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Vuille, M., Francou, B., Wagnon, P., Juen, I., Kaser, G., Mark, B. G., et al. (2008). Climate change and tropical Andean glaciers: Past, present and future. Earth-Science Reviews, 89(3-4), 79–96.
Abstract: Observations on glacier extent from Ecuador, Peru and Bolivia give a detailed and unequivocal account of rapid shrinkage of tropical Andean glaciers since the Little Ice Age (LIA). This retreat however, was not continuous but interrupted by several periods of stagnant or even advancing glaciers, most recently around the end of the 20th century. New data from mass balance networks established on over a dozen glaciers allows comparison of the glacier behavior in the inner and outer tropics. It appears that glacier variations are quite coherent throughout the region, despite different sensitivities to climatic forcing such as temperature, precipitation, humidity, etc. In parallel with the glacier retreat, climate in the tropical Andes has changed significantly over the past 50-60 years. Temperature in the Andes has increased by approximately 0.1 degrees C/decade, with only two of the last 20 years being below the 1961-90 average. Precipitation has slightly increased in the second half of the 20th century in the inner tropics and decreased in the outer tropics. The general pattern of moistening in the inner tropics and drying in the subtropical Andes is dynamically consistent with observed changes in the large-scale circulation, suggesting a strengthening of the tropical atmospheric circulation. Model projections of future climate change in the tropical Andes indicate a continued warming of the tropical troposphere throughout the 21st century, with a temperature increase that is enhanced at higher elevations. By the end of the 21st century, following the SIZES A2 emission scenario. the tropical Andes may experience a massive warming on the order of 4.5-5 degrees C. Predicted changes in precipitation include an increase in precipitation during the wet season and a decrease during the dry season, which would effectively enhance the seasonal hydrological cycle in the tropical Andes. These observed and predicted changes in climate affect the tropical glacier energy balance through its sensitivity to changes in atmospheric humidity (which governs sublimation), precipitation (whose variability induces a positive feedback on albedo) and cloudiness (which controls the incoming long-wave radiation). In the inner tropics air temperature also significantly influences the energy balance, albeit not through the sensible heat flux, but indirectly through fluctuations in the rain-snow line and hence changes in albedo and net radiation receipts. Given the projected changes in climate, based on different IPCC scenarios for 2050 and 2080, simulations with a tropical glacier-climate model indicate that glaciers will continue to retreat. Many smaller, low-lying glaciers are already completely out of equilibrium with current climate and will disappear within a few decades. But even in catchments where glaciers do not completely disappear, the change in streamflow seasonality, due to the reduction of the glacial buffer during the dry season, will significantly affect the water availability downstream. In the short-term, as glaciers retreat and lose mass, they add to a temporary increase in runoff to which downstream users will quickly adapt, thereby raising serious sustainability concerns. (C) 2008 Elsevier B.V. All rights reserved.
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2007 |
Berthier, E., Arnaud, Y., Kumar, R., Ahmad, S., Wagnon, P., & Chevallier, P. (2007). Remote sensing estimates of glacier mass balances in the Himachal Pradesh (Western Himalaya, India). Remote Sens. Environ., 108(3), 327–338.
Abstract: Although they correspond to an important fraction of the total area of mountain glaciers (33,000 km(2) out of 546,000 km(2)), Himalayan glaciers and their mass balance are poorly sampled. For example, between 1977 and 1999, the average area surveyed each year on the field was 6.8 km(2) only. No direct mass balance measurement is available after 1999. To contribute to fill this gap, we use remote sensing data to monitor glacier elevation changes and mass balances in the Spiti/Lahaul region (32.2 degrees N, 77.6 degrees E, Himachal Pradesh, Western Himalaya, India). Our measurements are obtained by comparing a 2004 digital elevation model (DEM) to the 2000 SRTM (Shuttle Radar Topographic Mission) topography. The 2004 DEM is derived from two SPOT5 satellite optical images without any ground control points. This is achieved thanks to the good onboard geolocation of SPOT5 scenes and using SRTM elevations as a reference on the ice free zones. Before comparison on glaciers, the two DEMs are analyzed on the stable areas surrounding the glaciers where no elevation change is expected. Two different biases are detected. A long wavelength bias affects the SPOT5 DEM and is correlated to an anomaly in the roll of the SPOT5 satellite. A bias is also observed as a function of altitude and is attributed to the SRTM dataset. Both biases are modeled and removed to permit unbiased comparison of the two DEM on the 915 km(2) ice-covered area digitized from an ASTER image. On most glaciers, a clear thinning is measured at low elevations, even on debris-covered tongues. Between 1999 and 2004, we obtain an overall specific mass balance of -0.7 to -0.85 m/a (water equivalent) depending on the density we use for the lost (or gained) material in the accumulation zone. This rate of ice loss is twice higher than the long-term (1977 to 1999) mass balance record for Himalaya indicating an increase in the pace of glacier wastage. To assess whether these ice losses are size-dependant, all glaciers were classified into three samples according to 2 their areal extent. All three samples show ice loss, the loss being higher for glaciers larger than 30 kin. In the case of the benchmark Chhota Shigri glacier, a good agreement is found between our satellite observations and the mass balances measured on the field during hydrological years 2002-2003 and 2003-2004. Future studies using a similar methodology could determine whether similar ice losses have occurred in other parts of the Himalaya and may allow evaluation of the contribution of this mountain range to ongoing sea level rise. (C) 2006 Elsevier Inc. All rights reserved.
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Blard, P. H., Lave, J., Pik, R., Wagnon, P., & Bourles, D. (2007). Persistence of full glacial conditions in the central Pacific until 15,000 years ago. Nature, 449(7162), 591–U10.
Abstract: The magnitude of atmospheric cooling during the Last Glacial Maximum and the timing of the transition into the current interglacial period remain poorly constrained in tropical regions, partly because of a lack of suitable climate records(1). Glacial moraines provide a method of reconstructing past temperatures, but they are relatively rare in the tropics. Here we present a reconstruction of atmospheric temperatures in the central Pacific during the last deglaciation on the basis of cosmogenic He-3 ages of moraines and numerical modelling of the ice cap on Mauna Kea volcano, Hawaii-the only highland in the central Pacific on which moraines that formed during the last glacial period are preserved(2). Our reconstruction indicates that the Last Glacial Maximum occurred between 19,000 and 16,000 years ago in this region and that temperatures at high elevations were about 7 degrees C lower than today during this interval. Glacial retreat began about 16,000 years ago, but temperatures were still about 6.5 degrees C lower than today until 15,000 years ago. When combined with estimates of sea surface temperatures in the central Pacific Ocean(3), our reconstruction indicates that the lapse rate during the Last Glacial Maximum was higher than at present, which is consistent with the proposal that the atmosphere was drier at that time(1,4). Furthermore, the persistence of full glacial conditions until 15,000 years ago is consistent with the relatively late and abrupt transition to warmer temperatures in Greenland(5), indicating that there may have been an atmospheric teleconnection between the central Pacific and North Atlantic regions during the last deglaciation.
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Lejeune, Y., Wagnon, P., Bouilloud, L., Chevallier, P., Etchevers, P., Martin, E., et al. (2007). Melting of snow cover in a tropical mountain environment in bolivia: Processes and modeling. J. Hydrometeorol., 8(4), 922–937.
Abstract: To determine the physical processes involved in the melting and disappearance of transient snow cover in nonglacierized tropical areas, the CROCUS snow model, interactions between Soil-Biosphere Atmosphere (ISBA) land surface model, and coupled ISBA/CROCUS model have been applied to a full set of meteorological data recorded at 4795 m MSL on a moraine area in Bolivia (16 degrees 17'S, 68 degrees 32'W) between 14 May 2002 and 15 July 2003. The models have been adapted to tropical conditions, in particular the high level of incident solar radiation throughout the year. As long as a suitable function is included to represent the mosaic partitioning of the surface between snow cover and bare ground and local fresh snow grain type (as graupel) is adapted, the ISBA and ISBA/CROCUS models can accurately simulate snow behavior over nonglacierized natural surfaces in the Tropics. Incident solar radiation is responsible for efficient melting of the snow surface (favored by fresh snow albedo values usually not exceeding 0.8) and also for the energy stored in snow-free areas (albedo = 0.18) and transferred horizontally to adjacent snow patches. These horizontal energy transfers (by conduction within the upper soil layers and by turbulent advection) explain most of the snowmelt and prevent the snow cover from lasting more than a few days during the wet season in this high-altitude tropical environment.
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Wagnon, P., Linda, A., Arnaud, Y., Kumar, R., Sharma, P., Vincent, C., et al. (2007). Four years of mass balance on Chhota Shigri Glacier, Himachal Pradesh, India, a new benchmark glacier in the western Himalaya. J. Glaciol., 53(183), 603–611.
Abstract: Little is known about the Himalayan glaciers, although they are of particular interest in terms of future water supply, regional climate change and sea-level rise. In 2002, a long-term monitoring programme was started on Chhota Shigri Glacier (32.2 degrees N, 77.5 degrees E; 15.7 km(2), 6263-4050 m a.s.l., 9 km long) located in Lahaul and Spiti Valley, Himachal Pradesh, India. This glacier lies in the monsoon-arid transition zone (western Himalaya) which is alternately influenced by Asian monsoon in summer and the mid-latitude westerlies in winter. Here we present the results of a 4 year study of mass balance and surface velocity. Overall specific mass balances are mostly negative during the study period and vary from a minimum value of -1.4 rn w.e. in 2002/03 and 2005/06 (equilibrium-line altitude (ELA) similar to 5180 m a.s.l.) to a maximum value of +0.1 rn w.e. in 2004/05 (ELA 4855 m a.s.l.). Chhota Shigri Glacier seems similar to mid-latitude glaciers, with an ablation season limited to the summer months and a mean vertical gradient of mass balance in the ablation zone (debris-free part) of 0.7 m w.e. (100 m)(-1), similar to those reported in the Alps. Mass balance is strongly dependent on debris cover, exposure and the shading effect of surrounding steep slopes.
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2005 |
Sicart, J. E., Wagnon, P., & Ribstein, P. (2005). Atmospheric controls of the heat balance of Zongo Glacier (16 degrees S, Bolivia). J. Geophys. Res.-Atmos., 110(D12), 17 pp.
Abstract: [1] Tropical glaciology includes investigation of climate variability in poorly documented regions of large surface-atmosphere energy exchanges. This study examines the surface energy fluxes of the Bolivian Zongo Glacier (16 degrees S, 68 degrees W, 6000 – 4900 m asl) in order to identify the atmospheric variables that control melting. Measurements from 1998 to 2000 taken from two meteorological stations in the ablation area are analyzed. During the progressive development of the wet season from September to January, melting energy was high: Solar irradiance was close to its summer solstice peak, clouds were sporadic, and albedo was low. During the core of the wet season from January to April the magnitudes of the net short-wave (+) and net long- wave (-) radiation fluxes were reduced by frequent clouds and snowfalls so that melting energy was moderate. In the dry season from May to August, melting energy was small because of the energy losses essentially in long-wave radiation but also in sublimation. The turbulent sensible heat flux to the ice (+) generally offsets the energy loss in latent heat (-), except in the dry season, when sublimation prevailed because of strong wind and dry air. Solar radiation was the main source of energy, but the seasonal changes of the melting energy were driven by long-wave radiation. In particular, clouds sharply increased the emittance of the thin high-altitude atmosphere. Closely linked to clouds and humidity, the main seasonal variables of low- latitude climates, long-wave radiation is a key variable in the energy balance of tropical glaciers.
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Vincent, C., Ribstein, P., Favier, V., Wagnon, P., Francou, B., Le Meur, E., et al. (2005). Glacier fluctuations in the Alps and in the tropical Andes. C. R. Geosci., 337(1-2), 97–106.
Abstract: This paper reports on glacier variations in two mountainous regions of the world, the Alps and the tropical Andes. Available records of snout position and glacier mass balance are compared and interpreted on a climatological basis. In both regions, there is a long-term decreasing trend over the 20th century. The yield of this trend is different from one glacier to the other, depending on geographic and geometric characteristics. Analysing the surface energy balance, net all wave radiation is the main energy flux at the glacier surface. The turbulent fluxes represent an important term with strong positive sensible heat flux in the Alps and strong negative latent heat flux (sublimation) in the Andes. Tropical glaciers are sensitive to inter-annual variations in solid precipitation that affects the albedo, whereas Alpine glaciers are strongly influenced by air temperature changes in the Alps. (C) 2004 Academic des sciences. Published by Elsevier SAS. All rights reserved.
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2004 |
Favier, V., Wagnon, P., Chazarin, J. P., Maisincho, L., & Coudrain, A. (2004). One-year measurements of surface heat budget on the ablation zone of Antizana Glacier 15, Ecuadorian Andes. J. Geophys. Res.-Atmos., 109(D18), 15 pp.
Abstract: Meteorological variables were recorded (14 March 2002 to 14 March 2003) at 4890 m above sea level (asl) on the Antizana Glacier 15 (0.71 km(2); 0degrees28'S, 78degrees09'W) in the tropical Andes of Ecuador (inner tropics). These variables were used to compute the annual cycle of the local surface energy balance (SEB). The four radiative fluxes were directly measured, and the turbulent fluxes were calculated using the bulk aerodynamic approach, calibrating the roughness length by direct sublimation measurements. The meteorological conditions are relatively homogeneous throughout the year (air temperature and air humidity). There is a slight seasonality in precipitation with a more humid period between February and June. During June-September, wind velocity shows high values and is responsible for intense turbulent fluxes that cause reduction of melting. Considering the SEB over the whole year, it is dominated by net radiation, and albedo variations govern melting. During the period under consideration the net short-wave radiation S (123 W m(-2)) and the sensible turbulent heat flux H (21 W m(-2)) were energy sources at the glacier surface, whereas the net long-wave radiation L (-39 W m(-2)) and the latent turbulent heat flux LE ( -27 W m(-2)) represented heat sinks. Since the OdegreesC isotherm-glacier intersection always oscillates through the ablation zone and considering that the phase of precipitation depends on temperature, temperature indirectly controls the albedo values and thus the melting rates. This control is of major interest in understanding glacier response to climate change in the Ecuadorian Andes, which is related to global warming and ENSO variability.
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Favier, V., Wagnon, P., & Ribstein, P. (2004). Glaciers of the outer and inner tropics: A different behaviour but a common response to climatic forcing. Geophys. Res. Lett., 31(16), 5 pp.
Abstract: We have compared the annual surface energy balance (SEB) of Zongo Glacier ( 16 degreesS, Bolivia, outer tropics) and Antizana Glacier 15 ( 0 degreesS, Ecuador, inner tropics). On annual time scale energy fluxes are very similar in the ablation zone: turbulent heat fluxes compensate each other and net short-wave radiation dominates the SEB. Albedo is central in controlling the melting. Consequently solid precipitation occurrence manages the annual mass balance variability. In the outer tropics, the annual melting is directly related to the annual distribution of precipitation, the period December – February being crucial. However, in the inner tropics, liquid precipitation can occur on the ablation zone, and snowline altitude remains very sensitive to air temperature. Tropical glaciers react rapidly to El Nino events, mainly because of an induced precipitation deficit in the outer tropics and to a temperature increase in the inner tropics, both leading to a rise in snowline altitude.
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L'Hote, Y., Chevallier, P., Etchevers, P., Lejeune, Y., & Wagnon, P. (2004). Rainfall or snowfall? Device for measuring the precipitation phase in the Bolivian Andes and analysis of the records. Hydrol. Sci. J.-J. Sci. Hydrol., 49(2), 273–281.
Abstract: The knowledge of the precipitation phase, solid or liquid, is important in high mountains, in order to use models of water and energy balances. During an experiment led in the Bolivian Andes, a complete weather station was installed at an altitude close to 4800 in, including two raingauge recorders, the first one with added antifreeze and oil, based on weight measurement, and the other one with tipping buckets. This device allowed a realistic partition of the liquid and solid phases in this region of tropical mountains, where the observed snow pack at the ground level is strongly influenced by the extremely high solar radiation and where the snow cover is ephemeral. The automation of the “raingauges” method, compared with several other classical methods, shows satisfactory results.
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2003 |
Delmas, R. J., Wagnon, P., Goto-Azuma, K., Kamiyama, K., & Watanabe, O. (2003). Evidence for the loss of snow-deposited MSA to the interstitial gaseous phase in central Antarctic firn. Tellus Ser. B-Chem. Phys. Meteorol., 55(1), 71–79.
Abstract: We have examined several MSA (methanesulfonic acid) records from the upper 200 m of the Antarctic ice street and in particular the new Dome F profile. At all the four sites studied, concentration profiles exhibit similar patterns as a function of depth. They suggest that snow metamorphism and solid phase migration are responsible for a marked release of gaseous MSA to interstitial firm air as kell as probably to the free atmosphere, in particular at extremely low accumulation sites. Snow acidity can also modify MSA concentration. It is proposed that, belong the upper few metres where the communication with the free atmosphere is possible, gaseous MSA may remain in the firn layers and be entrapped later in air bubbles at pole close-off. i.e. when firn is transformed into ice. Chemical measurements on the firn core do not take into account the MSA released to the gaseous phase. but this fraction is measurable in ice samples. In spite of these alterations occurring in the firn layers, relative charges of the atmospheric MSA concentration in the past are probably still there deep within the Antarctic ice street. However. for glacial periods, different processes have to he considered in relation to modified aerosol properties.
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Francou, B., Vuille, M., Wagnon, P., Mendoza, J., & Sicart, J. E. (2003). Tropical climate change recorded by a glacier in the central Andes during the last decades of the twentieth century: Chacaltaya, Bolivia, 16 degrees S. J. Geophys. Res.-Atmos., 108(D5), 12 pp.
Abstract: [1] The reasons for the accelerated glacier retreat observed since the early 1980s in the tropical Andes are analyzed based on the well-documented Chacaltaya glacier (Bolivia). Monthly mass balance measurements available over the entire 1991-2001 decade are interpreted in the light of a recent energy balance study performed on nearby Zongo glacier and further put into a larger-scale context by analyzing the relationship with ocean-atmosphere dynamics over the tropical Pacific-South American domain. The strong interannual variability observed in the mass balance is mainly dependent on variations in ablation rates during the austral summer months, in particular during DJF. Since high humidity levels during the summer allow melting to be distinctly predominant over sublimation, net all-wave radiation, via albedo and incoming long-wave radiation, is the main factor that governs ablation. Albedo depends on snowfall and a deficit during the transition period and in the core of the wet season (DJF) maintains low albedo surfaces of bare ice, which in turn leads to enhanced absorption of solar radiation and thus to increased melt rates. On a larger spatial scale, interannual glacier evolution is predominantly controlled by sea surface temperature anomalies (SSTA) in the eastern equatorial Pacific (Nino 1+2 region). The glacier mass balance is influenced by tropical Pacific SSTA primarily through changes in precipitation, which is significantly reduced during El Nino events. The more frequent occurrence of El Nino events and changes in the characteristics of its evolution, combined with an increase of near-surface temperature in the Andes, are identified as the main factors responsible for the accelerated retreat of Chacaltaya glacier.
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Wagnon, P., Sicart, J. E., Berthier, E., & Chazarin, J. P. (2003). Wintertime high-altitude surface energy balance of a Bolivian glacier, Illimani, 6340 m above sea level. J. Geophys. Res.-Atmos., 108(D6), 14 pp.
Abstract: [1] The objective of this study is to evaluate the surface energy balance (SEB) of a cold, high-altitude tropical glacier, Illimani (16degrees39'S; 67degrees47'W, 6340 m above sea level (asl)), where a 137 m ice core was drilled down to the bedrock in June 1999. During the dry austral winter, tropical glaciers are known to experience strong sublimation, which may be responsible for snow composition changes through postdepositional processes. In order to help toward the interpretation of this climatic archive, SEB experiments were carried out in 1999, 2001, and 2002, during the dry season (mostly clear and cold atmosphere, strong westerly winds). The daily net all-wave radiation is usually negative during this austral dry winter because of the highly reflective snow surface and because of reduced incoming long-wave radiation due to a low cloudiness compared to outgoing long-wave radiation. The turbulent heat fluxes were evaluated using the bulk aerodynamic approach, including stability correction. The roughness parameters are deduced from direct sublimation measurements and serve as calibration parameters. The sensible heat flux strongly heats the surface at night but changes to negative values during daytime unstable conditions (between 1000 and 1600 LT). The latent heat flux is always negative, which means that the surface loses mass through sublimation, particularly in the daytime (sublimation rates are -1.2 mm w.e. d(-1), -0.7 mm w.e. d(-1), and -0.8 mm w.e. d(-1) during the 2001, 2002, and 1999 measuring periods, respectively, where w.e. is water equivalent). The winter SEB of this high-altitude cold tropical glacier is comparable to the summer SEB over snow surfaces of the intermediate slopes of Antarctica.
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2001 |
Sicart, J. E., Ribstein, P., Wagnon, P., & Brunstein, D. (2001). Clear-sky albedo measurements on a sloping glacier surface: A case study in the Bolivian Andes. J. Geophys. Res.-Atmos., 106(D23), 31729–31737.
Abstract: An important potential source of error in snow albedo measurements under clear sky is the tilt of the surface when the sensors are placed parallel to the horizon. The error depends on the surface slope and aspect. A hemispherical radiation sensor receives its signal from within a surface area of several square meters., which generally is not a plane. Here we examined the influence of slope and aspect combinations related to surface irregularities on albedo measurements at two locations on the Zongo Glacier, Bolivia. The slope and aspect distributions determined through topographic measurements were used to correct the albedo measurements. The corrections were different between the two sites but resulted in similar albedo changes: the substantial albedo reductions observed from morning until evening were measurement artifacts. Even for slight slopes. an error of a few degrees on the slope estimation or an error of roughly 20degrees on the aspect estimation had an appreciable influence on the corrections, If the topography around the measurement site is not precisely, known, the most reliable method for determining the daily albedo is to observed the measurements around solar noon. Corrected albedo diurnal variations were loan and symmetrical. centered on a minimum at noon. During the dry season (the Southern Hemisphere winter), the diurnal fluctuations of the snow albedo on the Zongo Glacier seem to be controlled by the incidence angle cycle of solar radiation.
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Wagnon, P., Ribstein, P., Francou, B., & Sicart, J. E. (2001). Anomalous heat and mass budget of Glaciar Zongo, Bolivia, during the 1997/98 El Nino year. J. Glaciol., 47(156), 21–28.
Abstract: During El Nino-Southern Oscillation (ENSO) warm events, outer tropics glaciers usually experience a deficit of precipitation, an increase of air temperature and a strongly negative mass balance. At Glaciar Zongo, Bolivia, this was particularly striking during the vigorous 1997/98 El Nino event, one of the strongest of the century, and which resulted in an annual depth of runoff two-thirds higher than normal. We compare the energy balance on the glacier between two contrasting cycles, 1996/97 (La Nina year) and 1997/98 (El Nino year). Due to a 1.3 degreesC increase of annual mean air temperature, the sensible-heat flux slightly increases from 6.1 to 9.8 W m(-2). During the El Nino year, sublimation is reduced, leaving more energy for melting (LE = -18.1 W m(-2) in 1996/97 and LE = -11.6 W m(-2) in 1997/98). The main factor responsible for the dramatic increase in melting is the net all-wave radiation, which is three times higher in 1997198 than in 1996/97 (48.7 and 15.8 W m(-2), respectively). This sharp increase of net all-wave radiation is related to the decrease of albedo due to the precipitation deficit.
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1999 |
Wagnon, P. (1999). Analyse du bilan d'energie d'un glacier tropical . Application a la relation glacier-climatThèse de l'Université Joseph-Fourier, Grenoble. Ph.D. thesis, , .
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Wagnon, P., Delmas, R. J., & Legrand, M. (1999). Loss of volatile acid species from upper firn layers at Vostok, Antarctica. Journal Of Geophysical Research-Atmospheres, 104(D3), 3423–3431.
Abstract: Significant natural artifacts in ice chemical records have been pointed out in recent preliminary glaciochemical studies carried out in central Antarctic areas with very low snow accumulation rates (generally less than 5 g cm(-2) yr(-1)). Several deep drilling operations are underway in these regions for long-term paleoclimatic reconstructions. A detailed glaciochemical study has been carried out at Vostok Station in order to investigate post deposition changes of ion concentrations in the snow and firn layers. The results show that, in general, concentration profiles of species such as Cl, F, and NO(3), partly deposited as gases, exhibit a rapid decrease in the first few meters, indicating that a fraction, sometimes major, of these compounds is expelled back in the atmosphere after deposition. Some redeposition process of the gases is likely in the upper firn layers. Surprisingly, a similar effect is found for methanesulfonate (MS), suggesting that this compound could have a gaseous component in central Antarctic regions. The data also show that Cl, F, NO,, and MSA may be slowly but significantly displaced in the firn layers by high sulfuric acid levels of volcanic origin. The drastic changes observed in the surface snow layers may severely question current interpretations of certain chemical data recovered in these areas and point out an urgent need for new field and laboratory experiments on the air-to-ice transfer processes prevailing under central Antarctic conditions.
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Wagnon, P., Ribstein, P., Francou, B., & Pouyaud, B. (1999). Annual cycle of energy balance of Zongo Glacier, Cordillera Real, Bolivia. Journal Of Geophysical Research-Atmospheres, 104(D4), 3907–3923.
Abstract: An 18-month meteorological data set recorded at 5150 m above sea level (asl) on Zongo Glacier, in the tropical Andes of Bolivia, is used to derive the annual cycle of the local energy balance and to compare it to the local mass balance. The roughness parameters needed to calculate the turbulent fluxes over the surface are deduced from direct sublimation measurements performed regularly on the field site and serve as calibration parameters. For the hydrological year September 1996 to August 1997, net all-wave radiation (16.5 W m(-2)) is the main source of energy at the glacier surface and shows strong fluctuations in relation to the highly variable albedo. An important peculiarity of tropical glaciers is the negative latent heat flux (-17.7 W m(-2)) indicating strong sublimation, particularly during the dry season. The latent heat flux is reduced during the wet season because of a lower vertical gradient of humidity. The sensible heat flux (6.0 W m(-2)), continuously positive throughout the year, and the conductive heat flux in the snow/ice (2.8 W m(-2)) also bring energy to the surface. There is a good agreement between the monthly ablation calculated by the energy balance and the ablation evaluated from stake measurements. The seasonality of the proglacial stream runoff is controlled by the specific humidity, responsible for the sharing of the energy between sublimation and melting.
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Wagnon, P., Ribstein, P., Kaser, G., & Berton, P. (1999). Energy balance and runoff seasonality of a Bolivian glacier. Global and Planetary Change, 22, 49–58.
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1998 |
Wagnon, P., Ribstein, P., Schuler, T., & Francou, B. (1998). Flow separation on Zongo Glacier, Cordillera Real, Bolivia. Hydrological Processes, 12(12), 1911–1926.
Abstract: Meltwaters collected from the proglacial stream escaping from Zongo Glacier (2.1 km(2)), Bolivia (16 degrees S), have been monitored in order to analyse the internal drainage system of an Andean glacier. Electrical conductivity has been measured sporadically between February 1995 and March 1996, during 26 one-day field surveys, under various meteorological conditions in summer and winter. The mixing-model technique based on the electrical conductivity is used for a quantitative separation of discharge which is derived from continuous water level registration. Tracer experiments (mainly uranine dye and NaCl salt) have been carried out from March to June 1997 to obtain information about the internal drainage system. In the tropical Andes, accumulation only occurs in austral summer, whereas ablation occurs throughout the year and is higher during the accumulation season, between November and March. The assumptions involved in the use of mixing models for analysis of glacial drainage structure are applicable for tropical glaciers because glacial conduits do not suffer complete closure, and are permanently supplied by meltwaters, even in wintertime. Two components of discharge are separated: an englacial flow originating from surface meltwater which is routed without chemical enrichment, and offering low electrical conductivity; and a subglacial one routed in contact with bedrock or sediments showing high ionic concentrations. Electrical conductivity of meltwater varies diurnally, inversely to discharge fluctuations. According to this behaviour, total discharge is mainly formed by the englacial component. The drainage structures for englacial and subglacial flow have to be widely interconnected, as indicated by diurnal variations of the subglacial discharge. Comparison of hydrograph separation based on conductivity and on O-18 isotope cofirms that the subglacial flow is influenced by surface melting. A hydrograph separation of the subglacial flow is proposed, between a diurnal variable component, composed of water coming from the englacial network, and a base flow, which may vary seasonally. The dye tracing experiments cofirm the drainage complexity of Zongo Glacier and demonstrate the interest of identifying three main drainage components. (C) 1998 John Wiley & Sons, Ltd.
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1996 |
Harrington, R. F., Bales, R. C., & Wagnon, P. (1996). Variability of meltwater and solute fluxes from homogeneous melting snow at the laboratory scale. Hydrological Processes, 10(7), 945–953.
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1994 |
Dominé, F., Thibert, E., Van Landeghem, F., Silvente, E., & Wagnon, P. (1994). Diffusion and solubility of HCl in ice : preliminary results. Geophysical Research Letters, 21(7), 601–604.
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