CR1.1

We have investigated the source and role of light absorbing impurities (LAI) deposited on the glaciers of the Olivares catchment, in Central Chile. LAI can considerably darken (lower ice albedo) the glacier surface, enhancing their melting. We combined chemical and mineralogical analyses of surface ice samples with field-based spectral reflectance measurements and laboratory analysis to investigate the nature and properties of LAI on the glacier surface. Using remote sensing-based albedo maps, we upscaled local information to glacier-wide coverage. We then used a model to evaluate the sensitivity of surface mass balance to a change in ice albedo. The across-scale surface sample analysis revealed a history of over half a century of LAI deposition. We found traces of mining residuals in glacier surface samples. The glaciers with highest mass loss in the catchment present enhanced concentrations of surface dust particles with low reflectance properties. Our results indicate that dust particles with strong light-absorbing capacity have been mobilized from anthropogenic sources and deposited on the nearby glacier surfaces, thus lowering their surface reflectance. Large scale assessment from satellite-based observations revealed darkening (ice albedo lowering) at most investigated glacier tongues from 1989 to 2018. Mass balance is sensitive to ice albedo changes. However, we believe that an accelerated winter and spring snow albedo decrease, triggered by surface impurities, might be responsible for the above-average mass balances encountered in this catchment.

How to cite: Barandun, M., Bravo, C., Grobety, B., Jenk, T., Fang, L., Naegeli, K., Rivera, A., Cisternas, S., Münster, T., and Schwikowski, M.: Anthropogenic Influence on Surface Changes at Olivares Glaciers, Central Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7864, https://doi.org/10.5194/egusphere-egu22-7864, 2022.

Glaciers play a crucial role in the hydrological cycle, providing water in summer when it is most needed for irrigation. Global warming is leading to glacier retreat and enhanced summer runoff in the short-term, which should occur until glaciers become small enough that there is an end to this glacial subsidy and a reduction of summer runoff. However, debris accumulation, as it may alter the surface energy balance, will modify the rate at which this happens and may represent an important negative feedback. For this reason, quantifying and explaining glacier change in the Hindu Kush Himalaya (HKH) region, notably its relation to changing debris cover, is of paramount importance, especially for a country like Afghanistan with water resources highly dependent on glacial meltwater. This study assessed changes in glaciers of Afghanistan using data for 2000, 2007, 2017 and 2020 based upon the analysis of country-wide Landsat data and innovative indices for mapping both ice and debris-covered glacier extent.

Results showed 2862.5±47.8 km² of total glacier area in the year 2000, decreasing by 45.9 km²to 2007 (i.e. 6.55 km² per year), by a further 112.0 km² by 2017 (i.e. 11.2 km² per year), and by a further 73 km² (i.e. 24.3 km² per year) by 2020; that is there is a progressive increase in retreat rates. Of the 231.2 km² (8.07 %) loss of glacier surface area between 2000 and 2020, almost 81% related to glaciers with a size ≤ 2.01 km², which accounted for 50% of the total glacier area in the year 2000. Decreases were more dominant in center and northern regions of the country, whilst the northeastern region, the most glaciated part of the country, showed lesser changes. Increases in total debris cover area were found in the northeastern region of the country where there were lower decreases in total glacier area, whilst there were noticeable decreases in total debris cover area observed in southern and southeastern regionss and higher decreases in total glacier area. This suggested that the ability of the glaciers to produce debris cover has regional significance in explaining whether glacier loss occurs.

Ice elevation significantly changed over the time; changes in minimum ice elevations were up to +53 m, higher in the north, south, and southeastern regions. Maximum ice elevations decreased by -88 m, suggesting loss of accumulation zones. However, the northeastern part had a positive increase in maximum accumulation zone heights +23 m, this indicates possibility of increases in accumulation area.  

These results revealed differences in the regional response of Afghan glaciers to climate change. In the next stage of this work, we will link the spatial distributions of glacier response to downstream populations to identify those regions most exposed to the effects of these climate changes.

How to cite: Shokory, J. A. N. and Lane, S.: Glacier retreat and debris cover evolution in the Afghan Hindu Kush Himalaya between 2000 and 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12976, https://doi.org/10.5194/egusphere-egu22-12976, 2022.

Rocky debris covers 30% of glacier ablation areas in High Mountain Asia and generally suppresses melt. However, remote sensing observations have shown no statistical difference in glacier thinning rates between areas with and without debris cover; the ‘debris cover anomaly’. This pattern is apparent at subregional and regional scales, even after controlling for the elevation differences between debris-covered and clean ice. 

Two primary hypotheses to explain this behaviour have interpreted the thinning patterns in terms of melt or ice supply differences. First, rapid melt at supraglacial ponds and ice cliffs could enhance ablation in debris-covered areas, and therefore thinning as well. These features cannot entirely compensate for the melt reduction under debris, so a second hypothesis interprets the anomaly to indicate differences in emergence velocity between debris-covered and clean ice. However, complete understanding of the problem is challenged by a scale gap: the prior process studies have focused on single glaciers, whereas the anomaly has been identified for subregional- to regional spatial scales. Furthermore, these hypotheses neglect numerous other differences between debris-covered and clean glaciers (e.g. topo-climatic situation, accumulation mechanisms), which could bias this comparison.

We overcome these limitations through a direct assessment leveraging diverse large datasets and modelling. We firstly estimate emergence velocities and map ice cliffs and supraglacial ponds on a glacier-by-glacier basis across High Mountain Asia. We additionally assess other factors that could contribute to unexpected specific mass balance patterns: thin debris melt enhancement, distinct topo-climatic settings and the importance of avalanching for debris-covered ice. To determine the contribution of each factor to the debris-cover anomaly, we develop a statistical metric of how anomalous sub-debris ablation rates are, based on the difference in ablation rates between debris-covered and clean ice, as well as its altitudinal pattern. We use this metric and systematically remove the influence of the above hypothesized controls from each glacier’s emergence-corrected thinning data (specific mass balance) in a full-factorial investigation.

Our results firstly demonstrate that although emergence velocity differences between clean and debris-covered ice are systematic across the region, they do not resolve the debris-cover anomaly at the subregional or regional scale (altitudinal ablation rates are more negative for debris than clean ice). We find that accounting for any additional factor reduces the strength of the debris anomaly at regional and subregional scales, and our full-factorial analysis suggests that multiple factors combine to explain the debris cover anomaly.  Our results indicate that both hypotheses are correct in their process understanding at the glacier scale (reduced emergence velocity under debris, substantial ice cliff and pond ablation contribution), but not in their interpretation of the debris cover anomaly. Rather, our results underline previous suggestions that debris-covered glaciers fundamentally differ from clean ice glaciers in terms of mass supply mechanisms (i.e. supported by avalanching) and ablation patterns, leading to distinctive geometric expression and dynamics, and that the debris anomaly results from the integration of these patterns across scales.

How to cite: Miles, E., Kneib, M., McCarthy, M., Fugger, S., and Pellicciotti, F.: Disentangling the debris-cover anomaly in High Mountain Asia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11054, https://doi.org/10.5194/egusphere-egu22-11054, 2022.

The thermal regime of glaciers and ice caps represents the internal distribution of ice temperatures. Accurate knowledge of the thermal regime is crucial to understand the dynamics and response of ice masses to climate change, and to model their evolution. The ice temperature for example strongly controls the plasticity and the deformation rate of the ice with higher temperatures encouraging movement, and whether a glacier can slide over its base. Although the assumption is that most ice masses in the Inner Tien Shan are polythermal, this has not been examined in appropriate detail so far. In this research, we investigate the thermal regime of the Grigoriev ice cap and the Sary-Tor glacier, both located in the Inner Tien Shan in Kyrgyzstan. A 3D thermo-mechanical higher-order model is applied. Input data and boundary conditions are inferred from a surface energy mass balance model, a historical air temperature and precipitation series, ice thickness reconstructions, and digital elevation models. Calibration and validation of the englacial temperatures is performed using historical borehole measurements on the Grigoriev ice cap, radar measurements for the Sary-Tor glacier and temperature measurements on other glaciers in the area. The results of this study reveal a polythermal structure of the Sary-Tor glacier and a cold structure of the Grigoriev ice cap. The difference is related to the larger amount of snow (insulation) and superimposed ice (release of latent heat) for the Sary-Tor glacier resulting in higher surface temperatures, especially in the accumulation area, which are subsequently advected downstream. Further, ice velocities are much lower for the Grigoriev ice cap compared to the Sary-Tor glacier with consequent lower advection rates. Since the selected ice masses are representative examples of the (Inner) Tien Shan glaciers and ice caps, our findings can be generalised allowing this to improve the understanding of the dynamics and future evolution of the studied ice masses as well as other glaciers and ice caps in the region.

How to cite: Van Tricht, L. and Huybrechts, P.: Thermal regime of the Grigoriev ice cap and the Sary-Tor glacier in the Inner Tien Shan, Kyrgyzstan., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2818, https://doi.org/10.5194/egusphere-egu22-2818, 2022.

The quantification of snow accumulation and the temporal evolution of the snow pack is essential when investigating the mass balance conditions of mountain glaciers. In particular, accumulation regions become smaller due to the gradual increase of the equilibrium line, thus reducing mass input into the glacier system. This will have severe consequences on ice flux and thus the mass balance conditions across many mountain regions worldwide. The mass redistribution within the accumulation regions is considerably influenced by migration of melt water in the snow and firn pack and the induced mass and density changes. Here, we study snow and firn processes at a high mountain accumulation plateau on 3470 m asl at Vernagtferner, Austria. Vernagtferner is a major glacier in the drainage basin of Rofenache, with an area of about 6.9 km², covering altitudes between 2900 m and 3550 m. A snow monitoring station, including an upward-looking ground penetrating radar (upGPR) was installed at the highest accumulation basin in 2018. This station allows the continuous determination of the snow pack stratigraphy and of the snow water equivalent (SWE) (Heilig et al. (2009, 2010), Schmid et al. 2014, Heilig et al., 2015). We compare numerical simulations of the 1-dimensional snow cover model SNOWPACK (Bartelt and Lehning, 2002), driven by automatic weather station data, with continuous observations of the installed upGPR system and bi-annual in-situ data. The analysed upGPR data enable continuous evaluation of the SNOWPACK simulations over several melt and accumulation seasons. The upGPR data show that even at high elevations frequent melt-freeze crusts develop during the accumulation period. Even though the crusts are several centimetres, melt water rapidly percolates trough these layers, once the snow pack reaches isothermal conditions in late spring. The simulation results demonstrate, that SNOWPACK is able to reproduce this fast advance of the melt front accurately, while the up-GPR measurements provide an independent proof of the model performance. These measurements also show that firn layers (previous summer surfaces) block water infiltration into depth only for a very short period, indicating that SWE measurements of glacier accumulation only provide realistic values, if carried out before or just at the onset of spring melt. This feasibility study provides important indication on how to extend such studies to larger glacier systems, also in less monitored regions, where in-situ data might be sparse.

How to cite: Lambrecht, A., Heilig, A., and Mayer, C.: Comparison of simulated and radar-determined accumulation and melt at a high glacier accumulation site in the Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8724, https://doi.org/10.5194/egusphere-egu22-8724, 2022.

The artificial reduction of glacier melt is gaining increased attention due to accelerated ice wastage with atmospheric warming. In Switzerland, active coverage of glaciers using geotextiles is performed at currently ten sites and since more than 15 years. The measures represent an efficient method to locally safeguard the operability of ski slopes or other touristic attractions. Furthermore, ideas for large-scale technical interventions to save glaciers using artificially produced snow were proposed, with considerable resonance in the international media.

Here, an assessment of the benefit and applicability, as well as the costs and the drawbacks of different techniques to artificially reduce glacier melt is presented. On the one hand, observational data (in situ and remote sensing) across the Swiss Alps are used to analyze the efficiency and the spatial extent of the applied technical measures in the past. On the other hand, an integrative model approach is presented for investigating the potential of large-scale artificial snow production to limit the retreat of an entire glacier over the 21^st century, including an evaluation of the related costs and risks.

Presently, about 0.18 km², or 0.02% of the total Swiss glacier area, are covered by geotextiles, with a doubling of the covered area since 2012. Up to 350,000 m³ of ice melt per year have been mitigated by this technique. It is estimated that 1 m³ of saved glacier ice comes at a cost of 0.6 to 7.9 CHF m^-3 yr^-1, depending on the type of installation and its location on the glacier. These relatively high costs are an indication for the considerable economic value attributed to glacier ice.

It is shown that artificial melt reduction is not scalable. Whilst local interventions can be efficient and profitable, climate scenario-based model results for large-scale interventions indicate that saving Alpine glaciers by technological solutions is neither achievable nor affordable. It is a challenge to adequately communicate this gap between feasible local-scale ice-melt reduction, and the impractical technological 'saving' of entire glaciers to a broader public.

How to cite: Huss, M.: On the benefit and cost of artificial glacier melt reduction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1808, https://doi.org/10.5194/egusphere-egu22-1808, 2022.

Glaciers in Central Asia provide essential water resources for an increasing socio-economic water demand. However, glacier ablation is spatio-temporally highly heterogeneous, revealing hot-spots of the complex glacier response to climate change. A darkening of glacier surfaces caused by varying sources ranging from light absorbing mineral particles and black carbon to organic matter such as algal bloom, impacts the surface energy balance of glaciers. The albedo of the bare-ice surface is particularly crucial in regard to the ablation magnitude.

In this study, we present across scale results of the dependence of glacier mass balance on surface albedo for a large number of glaciers in the Tien Shan and Pamir Mountains. We used over 3000 surface reflectance scenes from the Landsat suite over the last two decades to produce distributed albedo maps. Annual mass balance time series are modelled using a temperature-index and distributed accumulation model for each glacier and year individually. The modelled estimates are annually calibrated with transient snowlines and further constrained by multiyear geodetic mass balances.

A comprehensive analysis of albedo variability and trends is performed at varying scales, ranging from pixel to catchment. A relationship between the distributed albedo information and the detected trends with the mass balance rates and variabilities is established. We highlight the sensitivity of glacier mass balance on surface albedo and stress the importance of the enhanced albedo feedback that will be amplified due to atmospheric warming and suspected darkening of glacier surfaces in the near future. This feedback will accelerate glacier melt and thus put the availability of melt water to river run off at sustainable risk. 

How to cite: Naegeli, K. and Barandun, M.: The Albedo-Ablation couple: a complex relationship with severe consequences, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6364, https://doi.org/10.5194/egusphere-egu22-6364, 2022.

Fedchenko Glacier, located in the central Pamir in Tajikistan, is the longest glacier in Asia. Due to its prominent location and its large size, it attracted scientific interest over the course of the twentieth and twenty first centuries, providing thus a rare legacy of historical data in Central Asia. In this study, we investigate a series of topographic data from 1928 to 2019. We use topographic maps collected during historical expeditions in 1928 and 1958. We take advantage of modern satellite data, such as KH-9 spy satellite (1980), SPOT5 (2010) and Pléiades (2017 and 2019). We also rely on ICESat campaign of 2003 and numerous GNSS surveys conducted in 2009, 2015, 2016 and 2019, which ensures a proper co-registration of the satellite data.

We calculate a mean rate of elevation change of -0.40 m/yr for 1928-2019, with a maximum thinning at the lowermost locations (approaching -0.90 m/yr). Despite this long-term thinning trend, we observe large contrasts between the sub-periods. The thinning rate of the tongue doubled for two sub-periods (1958-1980 and 2010-2017) compared to the long-term average. The ERA5 reanalysis (1950-2020) and the Fedchenko meteorological station records (1936-1991) reveal a dry anomaly in 1958-1980, followed by a wet anomaly in 1980-2010, which might have compensated for the temperature increase and thus mitigated mass losses. This wet anomaly could be an important feature of the “Pamir-Karakoram” anomaly, characterized by limited glacier mass losses in this region during the early twenty-first century. Our work contributes to better constrain the decadal glacier thickness changes, with unprecedented temporal resolution. This opens the way for more sophisticated approaches that link the glacier response to climate variability over decades.

How to cite: Brun, F., Lambrecht, A., Mayer, C., Berthier, E., Dehecq, A., Rezaei, J., and Deschamps-Berger, C.: Multi-temporal elevation changes of Fedchenko Glacier, Tajikistan (1928-1958-1980-2010-2017-2019), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5833, https://doi.org/10.5194/egusphere-egu22-5833, 2022.

Mountain glaciers and ice caps are undergoing rapid mass loss but rates of contemporary change lack long-term (centennial-scale) context. Future projections of glacier changes require spin up to present day conditions and thus baseline ice extents and ice volumes are a prerequisite for model validation. Here, we reconstruct the Little Ice Age maximum glacier extent and ice surface of Jostedalsbreen, which is the largest ice mass in mainland Europe. Jostedalsbreen had its largest Little Ice Age (LIA) maximum about 1740 to 1860. The LIA ice-covered area was 568 km² and the LIA ice volume was between 61 km³ and 91 km³. We show that the major outlet glaciers have lost at least 110 km² or 19 % of their LIA area and 14 km³ or 18 % of their LIA volume until 2006. The largest proportional changes are associated with the loss of ice falls and consequent disconnection of tributaries. Glacier-specific hypsometry changes suggest a mean rise in ELA of 135 m but there is wide inter-glacier variability. A median date for the LIA of 1755 suggests that the long-term rate of ice mass loss has been 0.05 m w.e. a^-1. Comparison of that long-term rate of mass loss with our other published analyses of changes to mountain glaciers and ice caps since the LIA shows that Jostedalsbreen is unusual in not exhibiting an acceleration in mass loss since the LIA. Indeed, we have reported a 23 % acceleration of glacier mass loss in NE Greenland and a doubling for the Southern Alps of New Zealand. Others have reported a doubling of the rate of mass loss for the Vatnajökull ice cap and for Patagonia since the LIA. We have very recently reported a ten-fold increase for ~ 15,000 glaciers across the Himalaya. A synthesis of these long-term analyses reveals a latitudinal effect, regional climate effects and local controls on long-term glacier mass balance. For example, local rates of loss across the Himalaya were enhanced with the presence of surface debris cover (by 2 times vs clean-ice) and/or a proglacial lake (by 2.5 times vs land-terminating). Overall, we highlight the utility of geomorphological-based reconstructions of glaciers for understanding and quantifying long-term (centennial-scale) responses of mountain glaciers and ice caps to climate and hence for understanding of meltwater production and proglacial landscape evolution.

How to cite: Carrivick, J., Yde, J., Andreassen, L., James, W., Sutherland, J., Lee, E., Quincey, D., Boston, C., and Grimes, M.: Glaciers and ice caps under climate change since the Little Ice Age, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1170, https://doi.org/10.5194/egusphere-egu22-1170, 2022.

Icelandic glaciers have been losing mass since the Little Ice Age in the mid-to-late 1800s, with higher mass loss rates in the early 21^st century, followed by a slowdown since 2011. As of yet, it remains unclear whether this mass loss slowdown will persist in the future. By reconstructing the contemporary (1958-2019) surface mass balance of Icelandic glaciers, we show that the post-2011 mass loss slowdown coincides with the development of the Blue Blob, an area of regional cooling in the North Atlantic Ocean to the south of Greenland. This regional cooling signal mitigates atmospheric warming in Iceland since 2011, in turn decreasing glacier mass loss through reduced meltwater runoff. In a future high-end warming scenario, North Atlantic cooling is projected to mitigate mass loss of Icelandic glaciers until the mid-2050s. High mass loss rates resume thereafter as the regional cooling signal weakens. 

How to cite: Noël, B., Aðalgeirsdóttir, G., Pálsson, F., Wouters, B., Lhermitte, S., Haacker, J. M., and van den Broeke, M. R.: North Atlantic cooling is slowing down mass loss of Icelandic glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3021, https://doi.org/10.5194/egusphere-egu22-3021, 2022.

Glaciers are considered to be a biome with diverse microbial life, and their meltwaters are highly influential to downstream ecosystems by creating a unique riverine habitat template and providing resources such as nutrients and organic matter. Yet, despite unprecedented rates of glacial retreat globally, not much is known about the fate of microbial cells exported from glaciers, despite their potential to colonize and reside in downstream ecosystems. The influence of glacial meltwater on these downstream ecosystems may persist far downstream, but other sources of nutrients, organic matter, and microbial cells within the hydrological catchment likely gain influence with distance from the glacier. These include soils and thawing permafrost - partly via eroding stream banks - and benthic stream biofilms residing both within and outside the glacial environment (e.g. in tributary streams).

In this work, we ask how suspended microbial assemblages change with increasing distance from the source glacier, especially in terms of their composition and corresponding with abiotic environmental factors. We hypothesize that OTU richness will increase with distance from source glaciers as the importance of other catchment sources increase. Specifically, we expect ‘cryospheric’ OTUs to decrease in relative abundance, and more ‘generalist’ freshwater OTUs to increase. We sampled five glacier-fed streams (3 in the Austrian Alps, 1 in Iceland and 1 in Greenland) from the glacier terminus until the ocean or major riverine outlet. DNA was extracted from samples, and 16s rRNA gene amplicons were sequenced to characterize the assemblage structure. These preliminary observations improve our knowledge of the fate of glacially-exported microbial assemblages, and help us to understand the extent of their potential impact for downstream ecosystems, especially in the current age of deglaciation.

How to cite: Jachnická, K., Kohler, T. J., Vinšová, P., Falteisek, L., Singer, G., Vrbický, T., and Stibal, M.: Longitudinal patterns of suspended microbial assemblages in glacier-fed streams., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4281, https://doi.org/10.5194/egusphere-egu22-4281, 2022.

Glaciers are a representative icon of the current climate change. They embody the three main aspects of this global phenomenon. They are (1) victims of the climate change, (2) an instrument of knowledge which allowed to better understand and address what is happening today, and (3) an important source of impact from climate change, both with respect to natural ecosystems and socio-economic activities.

One aspect related to the retreat of glaciers that is currently poorly investigated, is the consequence on the perception of the mountain environment and on our cultural heritage. Our approach to glaciers has deeply changed with time. During the Little Ice Age, they were regarded as a menace capable of destroying pastures and the highest settlements because of their advance. Then the view changes and glaciers became a sublime component of the landscape, interesting to know and study. Finally, glaciers turned into a source of entertainment for alpinists and tourists. Despite these different perspectives have somehow partially survived the passing of time, now the dominant perception of glaciers regards them as an endangered species. This is because of climate change and in many regions of Earth this vision will change soon: from endangered to extinct species (Carey, 2007).

Among the many environmental and socio-economic consequences, there is also the risk that with melting ice we will lose an important part of our culture. Retreating glaciers are sharing with us important messages, significantly contributing to strengthen the environmental awareness, what will happen when glaciers will be completely disappeared from whole mountain ranges? Will we be able to preserve what they have taught?

From this point of view the Dolomite represent an interesting laboratory to explore, ahead of other Alpine sectors, the effects of deglaciation in a renowned mountain range, with emphasis on the cultural impacts of glacier disappearance. These mountains, among the most famous and frequented of the Earth, hosted several small glaciers characterized by a notable morphological variety, but this glaciological heritage will soon disappear, as the Dolomites are expected to be ice-free in a few decades (Santin et al., 2019). There is a real risk that the Dolomite glaciers will vanish into silence and that with them we will also lose the stories of those who discovered, studied and attended those same glaciers. The aim of the present work is to oppose this fate, reviewing the recent history of Dolomitic glaciers and discussing the human and scientific significance of their demise.

References

• Carey (2007) The history of ice: how glaciers became an endangered species, Environmental History 12:497-527.
• Santin et al. (2019) Recent evolution of Marmolada glacier (Dolomites, Italy) by means of ground and airborne GPR surveys, Remote Sensing of the Environment 235:111442.

How to cite: Baccolo, G. and Varotto, M.: Mountains with no ice: deciphering the disappearance of glaciers in a renowned mountain range, the Dolomite case (Eastern Alps), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9821, https://doi.org/10.5194/egusphere-egu22-9821, 2022.

The excess meltwater that results from climate change induced mass loss of mountain glaciers is an important contributor to sea level rise (SLR). Up to now, large scale glacier observations and models have been used to estimate the amount of generated excess meltwater and its transient contribution to SLR under the assumption that meltwater is added to the ocean instantaneously and in its entirety. However, hydrological processes and water consumption during the transit from glacier to the ocean may affect the amount and timing of glacier runoff that eventually drains into the ocean. We hypothesize that some of the lost glacier ice may not reach the ocean at all or only at a much later stage.

In this study, we assessed the impacts of the hydrological pathway of meltwater from the glacier snouts to the ocean in the Indus Basin. With its large glacier ice reserves, relatively arid climate and large irrigation scheme, this basin provides the optimal case study for such an assessment. We coupled output from a detailed glacier model to the fully distributed hydrological model PCR-GLOBWB 2, and forced the models with bias-corrected historical and future climate data from the third phase of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3).

Our findings show that, particularly in (periods of) dry years, considerable fractions of excess glacier meltwater do not enter the ocean. The changes in hydrological stores indicate that much of it is withdrawn for surface water irrigation of cropland and eventually evaporates as a result. The increased surface water availability due to the presence of excess glacier meltwater leads to a lowering of groundwater irrigation and a reduction of the unsustainable depletion of the basin’s groundwater store. In the future, increased availability of excess glacier meltwater and increased water withdrawals due to continued climate change and socioeconomic developments exacerbate these effects. Up to the end of century, depending on the specific climate scenario, around 12% of excess glacier meltwater does not enter the ocean directly.

We conclude that not all glacier mass loss can be assumed to contribute (directly) to SLR, which may lead to overestimation of future sea level rise. Further research is necessary to estimate the breadth of these effects at a global scale, but we hypothesize that this may also play a role in other glacierized basins with semi-arid downstream regions and considerable distances between the glaciers and the ocean.

How to cite: Kraaijenbrink, P., Sutanudjaja, E., van de Wal, R., Bierkens, M., and Immerzeel, W.: Mass loss of mountain glaciers does not translate directly to sea level rise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4166, https://doi.org/10.5194/egusphere-egu22-4166, 2022.

With the ongoing, rapid glacier retreat, high-alpine landscapes are poised to change drastically over the coming decades. The newly exposed areas will not only give rise to new environments that can be eventually colonized by plants and organisms, but also to characteristic landforms. Amongst these, future glacier lakes forming in topographical depressions left behind by glacier retreat, have already been in the focus of earlier studies. The interest in these features is given by a number of factors, ranging from the ecological significance of such high-alpine lakes, over the potential hazards posed by such newly emerging water bodies, to their optical appeal in terms of landscape elements.

Here, we add to the existing body of literature dealing with the formation of new glacier lakes, and do so by leveraging both (1) a recently released, measurement-based estimate for the subglacial topography of all glaciers in the Swiss Alps, and (2) the results of a regional-scale glacier evolution model driven by different climate scenarios. Whilst the first point significantly increases the robustness of our projections, the second allows for a first quantification of the timing by which such new glacier lakes are expected to emerge. In this time-dependent analysis, we also include the possibility for newly emerging lakes to disappear again due to re-filling with sediments – a process neglected by studies so far.

Our results indicate that, if glaciers were to disappear entirely from the Swiss Alps, up to 683 new glacier lakes could emerge. These hold the potential of storing up to 1.16 ± 0.16 km³ of water, for a total lake area of 45 ± 9 km². For a middle-of-the-road climate scenario, we estimate that about 14% of the total volume (i.e. 0.16 ± 0.07 km³) could emerge by 2050. For 2100, the number changes to 57% (0.66 ± 0.17 km³), indicating a substantial increase in the pace by which new lakes will emerge after mid-century. Our first-order assessment of lake re-sedimentation indicates that about 45% of the newly emerging glacier lakes (ca. 260 out of ca. 570) could disappear again before the end of the century, and that between 12 to 20% of the newly emerging lake volume could be lost again due to this process. This suggests that sedimentation processes have to be taken into account when aiming at anticipating how future glacier landscapes will look like.

How to cite: Farinotti, D., Steffen, T., Huss, M., Estermann, R., and Hodel, E.: Future glacier lakes in the Swiss Alps: a projection of their evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-53, https://doi.org/10.5194/egusphere-egu22-53, 2022.

Global climate model projections suggest that 21st century climate change will bring significant drying in the terrestrial midlatitudes. Recent glacier modeling suggests that runoff from glaciers will continue to provide substantial freshwater in many drainage basins, though the supply will generally diminish throughout the century. In the absence of dynamic glacier ice within global climate models (GCMs), a comprehensive picture of future drought conditions in glaciated regions has been elusive. We evaluate glacial buffering of droughts in the Standardized Precipitation-Evapotranspiration Index (SPEI), which we calculate by combining CMIP5 climate model output with glacial runoff projections from GloGEM.

We find that accounting for glacial runoff tends to increase multi-model ensemble mean SPEI (wetter baseline) and reduce drought frequency and severity, even in basins with glacier cover of <2% by area.  We also find that the strength and future trend of glacial drought buffering depends on basin aridity index and glacial cover, and does not depend on other characteristics such as total basin area or latitude.  Glacial drought buffering persists even as glacial runoff is projected to decline through the 21st century.

How to cite: Ultee, L., Coats, S., and Mackay, J.: Glacial drought buffering through the 21st century, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13295, https://doi.org/10.5194/egusphere-egu22-13295, 2022.