CR1.4

Glacier mass balance is an essential component of the water budget of high-elevation and high-latitude regions, and yet this process is rather oversimplified in most hydrological models. This oversimplification is particularly relevant when it comes to representing two mechanisms: ice flow dynamics and melt beneath a supraglacial debris cover. In 2010, Huss et al. proposed a parsimonious approach to account for  glacier dynamics in hydrological models without solving complex equations of three-dimensional ice flow, the so-called delta-h parametrization. On the other hand, accounting for melt of debris-covered ice is still challenging as  estimates of debris thickness are rare. 

Here, we leveraged a distributed dataset of glacier-thickness change to derive a glacier-specific delta-h parametrization for 54 glaciers across the Aosta Valley (Italy), as well as  develop a novel approach for modeling melt beneath supraglacial debris based on residuals between locally observed change in thickness and that expected by regional elevation gradients. This approach does not require any on-the-ground data on debris cover, and as such it is particularly suited for ungauged regions where remote sensing is the only, feasible source of information for modeling. 

We found an expected, significant variability in both the delta-h parametrization and residuals over debris-covered ice across glaciers, with somewhat steeper orographic gradients in the former compared to the curves originally proposed by Huss et al. for Swiss glaciers. At a regional scale, the glacier mass balance showed a clear transition between a regime dominated by active glacier flow above 2,300 m ASL and a debris-dominated regime below this elevation threshold, which makes accounting for melt in the debris-covered area essential to correctly capture the future fate of low-elevation glaciers. Implementing the delta-h parametrization and our proposed approach to melt beneath supraglacial debris into S3M, a distributed cryospheric model, yielded an improved realism in estimates of future changes in glacier geometry  compared to assuming non-dynamic downwasting.

How to cite: Avanzi, F., Gabellani, S., Cremonese, E., Morra di Cella, U., and Huss, M.: Coupling the delta-h parametrization with melt beneath a supraglacial debris cover: an evaluation across 54 glaciers in the southern European Alps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-59, https://doi.org/10.5194/egusphere-egu21-59, 2021.

We characterize the spatiotemporal variations surface velocity of glaciers on the Kenai Peninsula, Alaska, using intensity offset tracking on a set of repeat-pass Sentinel-1 data and TerraSAR-X data. We derived 92 velocity fields and generated time-averaged annual and seasonal surface velocity maps for the period October 2014 to December 2019, as well as time series surface velocity profiles along centerlines for individual glaciers. We find considerable spatial and seasonal variations in surface velocity in the study area, especially a pronounced average spring speedup of 50% averagely compared to annual mean velocity. Ice velocities varied systematically between glaciers with different terminus types. Generally, the pixel-averaged velocity of tidewater and lake-terminating glaciers are up to 2 and 1.5 times greater than those of the land-terminating glaciers, respectively. For Bear glacier, with the analysis of surface velocity profile and the terminus change, we state this glacier retreat and accelerate. While the time-series result shows the velocity speed-up of the Bear glacier synchronizes well with the ice-damaged lake outburst flood (GLOF) events.

How to cite: Yang, R., Hock, R., Kang, S., Shangguan, D., and Guo, W.: Surface velocity variations of glaciers on Kenai Peninsula, Alaska, 2014-2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16020, https://doi.org/10.5194/egusphere-egu21-16020, 2021.

Proglacial lakes are becoming ubiquitous at the termini of many glaciers worldwide, leading to increased glacier mass loss and terminus retreat due to the influence such lakes are having upon ice dynamics. However, despite the highly dynamic nature and relative insensitivity to climate of many lake-terminating glaciers, an understanding of the key processes forcing their behaviour is lacking. As a result, it is difficult at present to accurately assess and predict the future response of these glaciers to continued warming. In addition, current methods of investigating lake-terminating glacier dynamics primarily involve the use of satellite remote sensing, which despite its clear importance in cryospheric studies does suffer from important limitations. A novel alternative is the use of repeat unmanned aerial vehicle (UAV) imagery, which can provide high resolution (cm-scale) imagery of the ice surface at varying spatial and temporal scales, depending on the needs of the researcher. As a result, this study utilised ultra-high resolution repeat UAV imagery to provide insights into the changing dynamics of Fjallsjökull, a lake-terminating glacier in southeast Iceland, over two periods during the 2019 summer melt season. The findings indicate that the overall dynamics of the glacier are controlled by the ~120 m deep subglacial channel under the study region, which is causing the glacier to flow faster as it enters deeper water, leading to increased ice acceleration, thinning and retreat. Such a correspondence between ice velocity and surface thinning suggests the implementation of the positive feedback mechanism “dynamic thinning” in this region of Fjallsjökull, with such heightened rates of surface thinning and frontal retreat continuing in future until the glacier recedes out of the subglacial channel into shallower water. Within this overall pattern, however, more localised, short-term changes in glacier dynamics are also observed which are likely to be forced primarily by subaqueous melting at the waterline, rather than being solely influenced by the basal topography. Although further work is required to add additional support to these findings, they clearly indicate the complex nature of the calving process and the dynamics of calving glaciers in general, highlighting the need for continued monitoring of lake-terminating glaciers at varying spatial and temporal scales.

How to cite: Baurley, N. and Hart, J.: Insights into the seasonal dynamics of the lake-terminating glacier Fjallsjökull, south-east Iceland, inferred using ultra-high resolution repeat UAV imagery, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-677, https://doi.org/10.5194/egusphere-egu21-677, 2021.

Meltwater from Himalayan glaciers sustains the flow of rivers such as the Ganges and Brahmaputra on which over half a billion people depend for day-to-day needs. Upstream areas are likely to be affected substantially by climate change, and changes in the magnitude and timing of meltwater supply are likely to occur in coming decades. About 10 % of the Himalayan glacier population terminates into pro-glacial lakes and such lake-terminating glaciers are known to be capable of accelerating total mass losses. However, relatively little is known about the mechanisms driving exacerbated ice loss from lake-terminating glaciers in the Himalaya. Here we examine a 2017-2019 glacier surface velocity dataset, derived from Sentinel 2 imagery, covering most of the Central and Eastern Himalayan glaciers larger than 3 km². We find that centre flow line velocities of lake-terminating glaciers are more than double those of land-terminating glaciers (18.8 vs 8.24 m yr^-1) and show substantially more heterogeneity around glacier termini. We attribute this large heterogeneity to the varying influence of lakes on glacier dynamics, resulting in differential rates of dynamic thinning, which effects about half of the clean-ice lake-terminating glacier population. Also, numerical ice-flow model experiments suggest that changes at the frontal boundary condition can play a key role in accelerating the glacier flow at the front. With continued warming new lake development is likely to happen and will further accelerate future ice mass losses, a scenario not currently considered in regional projections. 

How to cite: Pronk, J. B., Bolch, T., King, O., Wouters, B., and Benn, D.: Proglacial Lakes Elevate Glacier Surface Velocities in the Himalayan Region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13311, https://doi.org/10.5194/egusphere-egu21-13311, 2021.

Debris-covered glaciers in the Himalaya are losing mass more rapidly than expected. Quantifying and understanding the behaviour of these glaciers under climate change requires the use of numerical glacier models that represent the important feedbacks between debris transport, ice flow, and mass balance. However, these approaches have, so far, lacked a robust representation of the distributed mass balance forcing that is critical for making accurate simulations of ice volume change. This study forces a 3D higher-order ice flow model, with the outputs from an ensemble of distributed models of present day and future mass balance of Khumbu Glacier, Nepal. Distributed mass balance modelling, using the open access COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) model (Sauter et al., 2020), was forced by three statistically downscaled climate models from the Coordinated Regional Climate Downscaling Experiment (CORDEX) project.

Climate models were selected based on their ability to reproduce observed present-day seasonality and to account for several future climate and monsoon scenarios, the latter being of particular importance for these summer-accumulation type glaciers. Two emission scenarios, RCP4.5 and RCP8.5, were also chosen to simulate glacier change to 2100. Statistical downscaling involved Quantile Mapping and Generalized Analog Regression Downscaling, and the efficacy of these approaches was informed by present day mass balance sensitivity studies. Downscaled daily climate data were trained with data from two weather stations to aid disaggregation to an hourly resolution.

The integration of the mass balance and ice flow models posed some interesting challenges. The COSIPY model was run as if Khumbu Glacier were a clean-ice glacier (with no supraglacial debris) with sub-debris ablation resolved in the ice flow model. The value of using distributed mass balance forcing is seen in the simulated present-day velocities in the Khumbu icefall, which give a better fit to remote-sensing observations than previous simulations using a simple elevation-dependent mass balance forcing. The simulated present-day glacier extent is considerably smaller than the existing glacier outline. The debris-covered tongue, known to be losing mass at an accelerating rate, is virtually absent from these results, and is indicative of a stagnant tongue that is now or very soon to be dynamically disconnected from the active upper reaches of Khumbu Glacier.

How to cite: Schlich-Davies, A., Rowan, A., Quincey, D., Ross, A., and Egholm, D.: Combining distributed glacier mass balance and ice flow models to improve projections of mass change for debris-covered Khumbu Glacier, Nepal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8663, https://doi.org/10.5194/egusphere-egu21-8663, 2021.

Cold firn is progressively transitioning to a temperate state under a changing climate. This process is expected to affect ice core records and the mass balance of cold and polythermal glaciers. Thus there is a need to gain better understanding of this transition and develop quantitative, physical models, to predict cold firn evolution under a range of climate scenarios.

Here we present the application of a distributed, fully coupled energy balance and sub-surface model, to simulate high-alpine cold firn at Colle Gnifetti over the period 2003–2018. For the first time, we force such a model with high-resolution, long-term, quality-checked meteorological data measured in closest vicinity of the firn site, at the highest weather station in Europe (Capanna Margherita, 4560 m a.s.l.). The model includes the spatial variability of snow accumulation rates, and is calibrated using several, partly unpublished high-altitude measurements from the Monte Rosa area.

Overall, the simulated firn temperature profiles reach a very good agreement in comparison with a large archive of borehole measurements. Our results show a 20 m-depth firn warming rate of 0.44 °C per decade. Moreover, we find that surface melt over the glaciated saddle is increasing by 3–4 mm w.e. yr^-2 (+29–36 % in 16 years) depending on the location, although with a large inter-annual variability. The simulation also indicates that atmospheric humidity is a prominent control over melt occurrence, with considerable amounts of sublimation taking place in dry conditions. Hourly-resolution analysis of the melt dynamics reveals a marked tendency towards frequent, small melt events (< 4 mm w.e.): these collectively represent a significant fraction of the total amounts.

How to cite: Mattea, E., Machguth, H., Kronenberg, M., van Pelt, W., Bassi, M., and Hoelzle, M.: Firn changes at Colle Gnifetti revealed with a high-resolution process-based physical model approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3274, https://doi.org/10.5194/egusphere-egu21-3274, 2021.

The Karakoram is an extensively glacierised mountain range in the western part of High Mountain Asia and constitutes an important source of fresh water for millions of people in the Indus Basin. Over the last years, the Karakoram has attracted increasing attention due to an anomalous glacier stability, which contrasts the progressing ice mass loss across the Himalaya. Decreasing summer temperatures and increasing winter precipitation have been proposed as potential causes for the anomaly. However, the lack of snow accumulation studies and long-term meteorological measurements above 3,000 m a.s.l. hampers the corroboration of this hypothesis. To quantify the spatial and temporal variability of snow accumulation in the central Karakoram, we followed the track of a Canadian research expedition from 1986. We reinvestigated eight sites between ca. 4,400 and 5,200 m a.s.l. in the connected accumulation zone of the Biafo and Hispar glaciers in 2019. Density measurements were performed in each snow pit down to the summer horizon of the previous year to quantify the elevation-dependent amount of annually accumulated snow. In addition, snow samples were collected from three selected pits for the analysis of rare earth elements and stable water isotopes to constrain the origin and seasonality of the deposited snow. Finally, we compared our recent measurements with the 30-year-old results from the Canadian research expedition as well as independent meteorological data.  In doing so we aim to evaluate the hypothesised increase in winter precipitation in this region.

How to cite: Groos, A. R., Mayer, C., Lambrecht, A., Erlwein, S., and Schwikowski, M.: Spatio-temporal variability of snow accumulation on the Biafo and Hispar glaciers in the central Karakoram, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12879, https://doi.org/10.5194/egusphere-egu21-12879, 2021.

Glaciers are key components of the water towers of Asia and as such are relied upon by large downstream communities for domestic, agricultural and industrial uses. They have experienced considerable shrinking over the last decades, with some of the highest rates of mass loss observed in the south-eastern part of the Tibetan Plateau, where mass loss is also accelerating.  Despite these rapid changes, Tibetan glaciers’ changing role in catchment hydrology remains largely unknown. Parlung No.4 Glacier is considered as a benchmark glacier in this region, since its meteorology, surface energy fluxes and mass-balance have been examined since 2006. It is a maritime glacier with a spring (April-May) accumulation regime , which is followed by a period of ablation during the Indian Summer Monsoon (typically June-September). Here, we conduct a glacio-hydrological study over a period of five decades (1978-2018) using a fully distributed model for glacier mass balance and runoff simulation (TOPKAPI-ETH). We force the model with ERA5-Land and China Meteorological Forcing Dataset (CMFD) climate reanalysis downscaled to a local weather station to reconstruct meteorological time series at an hourly resolution. TOPKAPI-ETH is calibrated and validated with automatic weather station data, discharge measurements, geodetic mass balance, stake measurements and snow cover data from MODIS. We find a very clear acceleration in mass loss from 2000 onwards, which is mostly explained by an increase in temperature. This influence however was initially compensated by an increase in precipitation until the 2000’s, which attenuated the negative trend. Our results also indicate that the increase in the liquid-solid precipitation ratio has reduced the amount of seasonal accumulation, exacerbating annual mass loss. We demonstrate that the southern westerlies and the associated spring precipitation have as much influence on the glacier mass balance and catchment discharge as the Indian Summer Monsoon, by controlling seasonal snowpack development, which simultaneously provides mass to the glacier and protects it from melting in the early stage of the monsoon.

How to cite: Jouberton, A., Shaw, T. E., Miles, E., Ren, S., Yang, W., Zhao, C., McCarthy, M., Fugger, S., Dehecq, A., and Pellicciotti, F.: Reconstructing the runoff and mass changes of a maritime Tibetan glacier since 1975, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14976, https://doi.org/10.5194/egusphere-egu21-14976, 2021.

The evolution of the Elbrus glacier complex, consisting of two dozen of glaciers, in the last two decades of the 20th century and at the beginning of the 21st century generally corresponded to the trend of a decrease in the glaciated area of ​​the whole Caucasus. Over the period 1960-2014, the area of ​​Elbrus glaciation decreased by approximately 15%, and over two decades 1997-2017 - by almost 11%. As of 2017, the area of ​​Elbrus glaciation was estimated to ca. 112 sq. km, its volume exceeded 5 cub. km. Elbrus glaciation contributes significantly to the formation of the hydrological regime in the region, and, therefore, may be considered as a major challenge ti the regional socio-economic development. The latter circumstance requires an accurate assessment of the glacial runoff, and, consequently, the calculation of the surface mass balance of the glacial complex. We use an energy balance model to calculate the current and future surface mass balance. The series of observations at the Terskol meteorological station, located fifteen kilometers from the southern spurs of Elbrus, and the Mestia meteorological station, located somewhat further, on the territory of Georgia on the southern slope of the Main Caucasian ridge, as well as data from automatic weather stations on Elbrus slopes and on Djankuat glacier a few tens of kilometers from Elbrus, were applied for model forcing to reproduce present surface mass balance. The modeling results were validated by comparison with the measured surfave mass balance components on Garabashi glacier, one of the glaciers on the southern slope of Elbrus. Climate projections until the end of the 21st century for the Elbrus region were composed on the basis of multi-model results of regional climate modeling within the CORDEX project for various scenarios.

We demonstrate that simultaneous surface air temperature and insolation growth accompanied by decrease in precipitation, predicted by multi-model regional climate modeling and downscaled to the Central Caucasus area, will cause essential lifting of the equilibrium line altitude and shrinking of accumulation area. As a result, we must expect an accelerated degradation of Elbrus glaciation in forthcoming decades.   

The reported study was funded by RFBR and RS, project number 21-55-100003

How to cite: Rybak, O., Dymova, T., Korneva, I., Kutuzov, S., Lavrentiev, I., Rybak, E., and Toropov, P.: Future surface mass balance of the Elbrus Glacial Complex under climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6422, https://doi.org/10.5194/egusphere-egu21-6422, 2021.

Subtropical Andean glaciers are losing mass in response to the long-term atmospheric warming and precipitation decrease. Extreme events as heat waves, however, seems to potentially play a key role in the sustained ice loss detected in the last decades. Increased frequency of heat wave events have been detected in the central valley of Chile, however, the occurrence and impact of these events on the Andean cryosphere remain unknown. The main reason is associated with the lack of meteorological observations at higher elevations in the Andes. 

In filling this gap, we present an assessment of the occurrence of heat waves in the glacierized Río Olivares basin (33°S), which comprise an elevation range between ~1500  and ~6000 m a.s.l. and where a strong ice loss has been detected during the last decades. The main aim is to analyse the correspondence of heat waves events occurred with those in the nearby city of Santiago located in the central valley of Chile and to assess the potential impacts of these events on the glaciers located in this basin. Using meteorological observations in Río Olivares basin and in Santiago between the years 2013 and 2020, heat wave events were determined. We estimated the heat wave events using the monthly 90th percentile and the adjustment of a harmonic function. An additional adjustment relative to the climate period 1981-2010 was also introduced. The results determined 66 events in the Río Olivares basin while in Santiago were 53 events. These results reveal high spatial variability in the occurrences of heat waves as only 49% of the events in Santiago were detected in the Río Olivares basin. Ongoing work is focused on analysing the impacts of these events over the glaciers of the basin. Here, through the use of the computed basin-scale 0°C isotherm, the relation between glacier area under melt (i.e. glacier area located below the 0°C isotherm) and the heat wave events will be shown. The findings of this works reinforce the need for more observational efforts over high elevations in the Andes in order to robustly assess and at a basin scale, the impact of extreme events on the Andean cryosphere.

How to cite: Bravo, C., Paredes, P., Donoso, N., and Cisternas, S.: Occurrence and impacts of heat waves events in a glacierized basin in the subtropical Andes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15063, https://doi.org/10.5194/egusphere-egu21-15063, 2021.