Observing and modelling glaciers at regional to global scales

The increasing availability of remotely sensed observations and computational capacity, drive modelling and observational glacier studies towards increasingly large spatial scales. These large scales are of particular relevance, as they impact policy decisions and public discourse. In the European Alps, for instance, glacier changes are important from a touristic perspective, while in High Mountain Asia, glaciers are a key in the region’s hydrological cycle. At a global scale, glaciers are among the most important contributors to present-day sea level change.

This session focuses on advances in observing and modelling mountain glaciers and ice caps at the regional to global scale. We invite both observation- and modelling-based contributions that lead to a more complete understanding of glacier changes and dynamics at such scales.

Contributions may include, but are not limited to, the following topics:
• Observation and modelling results revealing previously unappreciated regional differences in glacier changes or in their dynamics;
• Large-scale impact studies, including glaciers' contribution to sea level change, or changes in water availability from glacierized regions;
• Advances in regional- to global-scale glacier models, e.g. inclusion of physical processes such as ice dynamics, debris-cover effects, glacier calving, or glacier surging;
• Regional to global scale process-studies, based on remote sensing observations or meta-analyses of ground-based data;
• Innovative combinations of observation and modelling techniques, for example blending different remote sensing products, or integrating machine learning algorithms;
• Inverse modelling of subglacial characteristics or glacier ice thickness at regional scales.

Note that this session is organized as a PICO.

Convener: Fabien Maussion | Co-conveners: Ines Dussaillant, Daniel Farinotti, Harry ZekollariECSECS
vPICO presentations
| Mon, 26 Apr, 13:30–15:00 (CEST)

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Ines Dussaillant, Harry Zekollari, Daniel Farinotti
Romain Millan, Jérémie Mouginot, Antoine Rabatel, and Mathieu Morlighem

The effects of climate change on water resources and sea level are largely determined by the size of the ice reservoirs around the world, which still remains largely uncertain. Ice flow defines the transfer of ice within a glacier and therefore largely governs the spatial distribution of the ice volume. Although some individual regions have been mapped, there is to date no global and complete view of glacier flow. In this study, we present a global mapping of surface ice flow velocity and use it to revise the ice thickness distribution and volume of glaciers around the world. Glacier surface flow velocities were calculated using Sentinel-2/ESA, Landsat-8/USGS, Venμs/CNES-ISA, Pléiades/AirbusD&S and radar data from Sentinel-1/ESA. We designed an automated workflow that (i) downloads the data from institutional or commercial servers, (ii) prepares the images, (iii) launches the feature tracking algorithm, (iv) calibrate the glacier surface velocities, and (v) mosaics the results to obtain filtered and averaged velocity maps. For years 2017 and 2018, glacier surface flow velocities are quantified for every possible repeat cycles from the nominal cycle of the sensor (2-16 days) up to more than one year. This new database of glacier surface flow velocity is used to construct an updated global ice volume based on the well known Shallow Ice Approximation approach. We discuss the quality of our global glacier surface flow velocity product and of our new ice volume reconstruction with respect to existing state of the art estimates and quantify the impact of our results in terms of sea level rise and water resources.

How to cite: Millan, R., Mouginot, J., Rabatel, A., and Morlighem, M.: Global mapping of surface flow velocity and re-evaluation of the volume of the world's glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1066,, 2021.

Lilian Schuster, David Rounce, and Fabien Maussion

A recent large model intercomparison study (GlacierMIP) showed that differences between the glacier models is a dominant source of uncertainty for future glacier change projections, in particular in the first half of the century.  Each glacier model has their own unique set of process representations and climate forcing methodology, which makes it impossible to determine the model components that contribute most to the projection uncertainty. This study aims to improve our understanding of the sources of large scale glacier model uncertainty using the Open Global Glacier Model (OGGM), focussing on the surface mass balance (SMB) in a first step. We calibrate and run a set of interchangeable SMB model parameterizations (e.g. monthly vs. daily, constant vs. variable lapse rates, albedo, snowpack evolution and refreezing) under controlled boundary conditions. Based on ensemble approaches, we explore the influence of (i) the parameter calibration strategy and (ii) SMB model complexity on regional to global glacier change. These uncertainties are then put in relation to a qualitative selection of other model design choices, such as the forcing climate dataset and ice dynamics model parameters. 

How to cite: Schuster, L., Rounce, D., and Maussion, F.: Impact of the choice of surface mass balance models and their calibration on large-scale glacier change projections, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1391,, 2021.

Beatriz Recinos, Fabien Maussion, Brice Noël, Marco Möller, and Ben Marzeion

Greenland's Peripheral Glaciers (PGs) are glaciers that are weakly or not connected to the Ice Sheet. Many are tidewater, losing mass via frontal ablation. Without comprehensive regional observations or enough individual estimates of frontal ablation, constraining model parameters remains a challenging task in this region. We present three independent ways to calibrate the calving parameterization implemented in the Open Global Glacier Model (OGGM) and asses the impact of accounting for frontal ablation on the estimate of ice stored in PGs. We estimate an average regional frontal ablation flux for PGs of 7.94±4.15 Gtyr-1 after calibrating the model with two different satellite velocity products, and of 0.75±0.55 Gt yr-1 if the model is constrained using frontal ablation fluxes derived from independent modelled Surface Mass Balance (SMB) averaged over an equilibrium reference period (1961-1990). This second method is based on the assumption that most PGs during that time have an equilibrium between mass gain via SMB and mass loss via frontal ablation. This assumption can serve as a basis to assess the order of magnitude of dynamic mass loss of glaciers when compared to the SMB imbalance. By comparing the model output after applying both calibration methods, we find that the model is not able to predict individual tidewater glacier dynamics if it relies only on SMB estimates and the assumption of a closed budget to constrain the model. The differences between the results from both calibration methods serve as an indication of how strong the dynamic imbalance might have been for PGs during that reference period.

How to cite: Recinos, B., Maussion, F., Noël, B., Möller, M., and Marzeion, B.: Calibration of a frontal ablation parameterization applied to Greenland's peripheral calving glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2926,, 2021.

Melissa Mengert and Ben Marzeion

Depending on the seasonality of temperature and precipitation, mountain glaciers seasonally store and release large amounts of freshwater. Therefore, glaciers have a strong influence on water availability in many regions of the world. In an ongoing global climate change, glaciers have an additional impact on water availability, as the net amount of stored ice changes in an unsustainable way. This results in glaciers not only altering the seasonal runoff, but also adding a net input into the drainage system.
To better understand the interplay between seasonal and long-term storage changes, we suggest to split the monthly seasonal mass balance into a sustainable fraction, which is derived by balancing solid precipitation by ablation proportional to positive temperatures, and an unsustainable fraction, which causes long-term glacier mass change.

Similarly, we consider the effect of glacier area changes, allowing us to separate seasonal runoff into components attributable to (unsustainable) area change, (unsustainable) mass change, or the (sustainable) seasonal runoff from the glacier.

By applying the concept to a reconstruction of global glacier change, we illustrate how the glacier input into river basins in different climatological settings has been affected by the glacier mass loss during the 20th century. 

How to cite: Mengert, M. and Marzeion, B.: The relevance of the past unsustainable increase of glacier runoff for large-scale basins in different climatological settings , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7700,, 2021.

Harry Zekollari, Regine Hock, Ben Marzeion, Fabien Maussion, and Lilian Schuster and the GlacierMIP3 participants

Glaciers outside the ice sheets are major contributors to today’s sea-level rise and are projected to remain so in the coming century. With the goal to better assess the future sea-level contribution from glaciers and to quantify related uncertainties, the Glacier Model Intercomparison Project (GlacierMIP) has set out to develop a series of coordinated experiments to be run as a community-wide effort.

The first two phases of the GlacierMIP have focused on the evolution of glaciers throughout the 21st century (Hock et al., 2019; Marzeion et al., 2020). In the third phase of GlacierMIP (GlacierMIP3 – equilibration), a new set of experiments has been designed to investigate the equilibration of glaciers under constant climate conditions. These experiments will allow us to answer the following fundamental questions:

1. What would be the equilibrium volume and area of all glaciers outside the ice sheets if global mean temperatures were to stabilize at present-day levels?

2. What would be the equilibrium volume and area of all glaciers outside the ice sheets if global mean temperatures were to stabilize at different temperature levels (e.g. +1.5, +2, relative to pre-industrial)?

3. For each of these global mean temperature stabilization scenarios, how much time would the glaciers need to reach their new equilibrium?

In this contribution, we present the experimental design of GlacierMIP3 and open up the floor for ideas and discussions about possible processing of these experiments. We also invite interested individuals and groups to join us to discuss the possibility of their model to be included in the newest phase of GlacierMIP.



GlacierMIP1: Hock, R., Bliss, A., Marzeion, B., Giesen, R.H., Hirabayashi, Y., Huss, M., Radic, V., Slangen, A.B.A. (2019), GlacierMIP – A model intercomparison of global-scale glacier mass-balance models and projections, Journal of Glaciology 65(251), 453-467, doi: 10.1017/jog.2019.22

GlacierMIP2: Marzeion, B., Hock, R., Anderson, B., Bliss, A., Champollion, N., Fujita, K., Huss, M., Immerzeel, W., Kraaijenbrink, P., Malles, J-H., Maussion, F., Radic, V., Rounce, D.R., Sakai, A., Shannon, S., van de Wal, R., Zekollari, H. (2020), Partitioning the Uncertainty of Ensemble Projections of Global Glacier Mass Change, Earth’s Future 8(7), e2019EF001470, doi: 10.1029/2019EF001470

How to cite: Zekollari, H., Hock, R., Marzeion, B., Maussion, F., and Schuster, L. and the GlacierMIP3 participants: GlacierMIP3 global glacier mass change equilibration experiments - rationale and experimental design, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7775,, 2021.

Taisiya Dymova, Oleg Rybak, Harry Zekollary, Matthias Huss, Irina Korneva, Afanasy Gubanov, and Gennady Nosenko

The retreat of glaciers of the Greater Caucasus in the second half of the 20th and early 21st centuries was recorded by a variety of methods, including both direct instrumental observations and remote sensing. It is natural to expect that in the conditions of a gradually warming climate, the general trend of glacier retreat will continue in the future.

In the foothills of the North Caucasus, an important agricultural region, the problem of expected changes in mountain glaciation is particularly acute, since fluctuations in the flow regime of local rivers depend on the evolution of glaciers: the contribution of glacial runoff to total discharge is very significant. Retreating glaciers can also cause lakes to appear in local depressions in the underlying relief. Their possible breakthrough could cause significant damage to the economy and threaten human lives. The forecast of runoff and lake formation are associated with the projections on the future state of mountain glaciation.

Here, we present the work in progress to assess the rate of future glacier change in the Central Caucasus throughout the 21st century. The aim is to determine how the characteristics of mountain glaciation (its area, volume, position of the glacier fronts) of the Central Caucasus will change, depending on the climate scenario. In order to accomplish this goal, we use the GloGEMflow model (Zekollari et al., 2019) with an updated radiation block (Rybak et al., 2021, in press) and a set of CMIP5/CMIP6 climate scenarios. The GloGEMflow model features an ice flow block which is calibrated to match the Huss & Farinotti (2012, updated to RGI6.0) glacier geometry data. Validation of the model is based on the assessment of discrepancies arising when comparing data about glaciers boundaries changes for the period from ~2000 (RGI6.0) to 2018 (Department of Glaciology RAS).

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

How to cite: Dymova, T., Rybak, O., Zekollary, H., Huss, M., Korneva, I., Gubanov, A., and Nosenko, G.: Modelling future evolution of glaciation in the Central Caucasus, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9032,, 2021.

Johannes Marian Landmann, Matthias Huss, Hans Rudolf Künsch, Christophe Ogier, Lea Geibel, Leo Sold, and Daniel Farinotti

As glaciers shrink, high interest in their near real-time mass balance arises. This is mainly for two reasons: first, there are concerns about water availability and short-term water resource planning, and second, glaciers are one of the most prominent indicators of climate change, resulting in a high interest of the broader public.

To satisfy both interests regarding information on near real-time mass balance, we are running the project CRAMPON – “Cryospheric Monitoring and Prediction Online”. Within this project, we set up an operational assimilation platform where it is possible to query daily mass balance estimates in near real-time, i.e. updated with a lag of max. 24 hours. During the operational alpha phase, we increase the amount of modelled glaciers and assimilated observations steadily. We start with about 15 glaciers from the Glacier Monitoring Switzerland (GLAMOS) program, for which time series of seasonal mass balances from the glaciological method are available. After that, we expand our set of modelled glaciers to about 50 glaciers that have frequent geodetic mass balances in the past, and finally to all glaciers in Switzerland. The assimilated observations reach from the operational GLAMOS seasonal mass balance observations via daily point mass balances from nine in situ cameras providing instantaneous ablation rates to satellite-derived albedo and snow distribution on the glacier.
As basis for the platform, we run an ensemble of three temperature index and one simplified energy balance melt models. This ensemble takes gridded temperature, precipitation and radiation as input and aims at quantifying uncertainties of the produced daily mass balances. To determine uncertainties in the model prediction of a current mass budget year correctly, we run the models with parameter distributions we have fitted on individual parameter sets calibrated in the past. Since a purely model-based prediction can reveal high uncertainties though, we choose a sequential data assimilation approach in the form of a Particle Filter to constrain this uncertainty with observations, whenever available. We have customized the standard Particle Filter to (1) use a resampling method that is able to keep models in the ensemble despite a temporary bad performance, and (2) allow parameter and model probability evolution over time.

In this contribution, we focus on giving a holistic overview over the already existing platform features and discuss the future developments. We plan to make the calculated mass balances publicly available in summer 2021, and to extend this platform to the global scale at a later stage.

How to cite: Landmann, J. M., Huss, M., Künsch, H. R., Ogier, C., Geibel, L., Sold, L., and Farinotti, D.: CRAMPON: a model- and observation-based near real-time platform for glacier mass balance monitoring in Switzerland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9761,, 2021.

Evaluating Simplified Numerical Models of Debris-Covered Glaciers
James C. Ferguson, Tobias Bolch, and Andreas Vieli
Ann-Sofie Priergaard Zinck and Aslak Grinsted

The ice thickness of the Müller Ice Cap, Arctic Canada, is estimated using regression parameters obtained from an inversion of the shallow ice approximation by the use of a single Operation IceBridge flight line in combination with the glacier outline, surface slope, and elevation. The model is compared with an iterative inverse method of estimating the bedrock topography using PISM as a forward model. In both models the surface elevation is given by the Arctic Digital Elevation Model. The root mean squared errors of the ice thickness on the ice cap is 131 m and 139 m for the shallow ice inversion and the PISM model, respectively. Including the outlet glaciers increases the root mean squared errors to 136 m and 396 m, respectively.

The simplicity of the shallow ice inversion model, combined with the good results and the fact that only remote sensing data is needed, means that there is a possibility of applying this model in a global glacier thickness estimate by using the Randolph Glacier Inventory. Most global glacier estimates only provide the volume and not the ice thickness of the glaciers. Hence, global ice thickness models is of great importance in quantifying the potential contribution of sea level rise from the glaciers and ice caps around the globe.

How to cite: Zinck, A.-S. P. and Grinsted, A.: Estimating the ice thickness of the Müller Ice Cap using an inversion of the shallow ice approximation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11602,, 2021.

Dan Goldberg, Louis Kinnear, Florian Kobierska-Baffie, Nans Addor, Helen He, Qianyu Zha, Nele Reyniers, and Fabien Maussion

Hundreds of millions of people depend strongly on hydrological inputs in the mountainous regions of China and central Asia. Glacier runoff is a major contributor to this hydrological forcing, yet many glaciers in the region have undergone mass loss in recent years and this mass loss is expected to continue or increase in response to climatological change. As such it is important to assess the large-scale response of High Mountain Asia glaciers to climate change , and its effects on hydrology. We present here preliminary modelling investigations of glacier change and hydrological impacts in response to high-resolution climate model projections over the 21st century as a component of the project SWARM (Impacts Assessment to Support WAter Resources Management and Climate Change Adaptation for China). Our model chain consists of i) Open Global Glacier Model (OGGM), which allows for high-resolution glacier flowline modelling of multiple glaciers, and ii) the Framework for Understanding Structural Errors (FUSE) a modular framework for snow and hydrology modelling, which we used to assemble and run three hydrological models over the whole of China. Both FUSE and OGGM are forced by an ensemble of bias-corrected CORDEX-East Asia regional climate models (in turn forced by CMIP5 general circulation models), and outputs of OGGM are provided to FUSE. We discuss our application of OGGM to 80,000 glaciers in Chinese river catchments; our efforts to calibrate the mass balance model using an expanded set of geodetic mass balance constraints; and finally the projections of glacier, snow and streamflow changes in the 21st century. In particular, we discuss the robustness and uncertainties in the projections as sampled by our multi-model ensemble.

How to cite: Goldberg, D., Kinnear, L., Kobierska-Baffie, F., Addor, N., He, H., Zha, Q., Reyniers, N., and Maussion, F.: Modelling climate change impacts on glaciers and water resources in China  using OGGM and FUSE, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12250,, 2021.

Christian Sommer, Thorsten Seehaus, Lukas Sochor, Philipp Malz, and Matthias Braun

The large ice caps and glaciers of the northern and southern polar regions have the potential to contribute significantly to global sea-level rise, yet measurements of glacier mass changes in those regions are scarce and difficult due to harsh conditions and the size of Arctic and Antarctic glacier areas. Acquisitions of the synthetic aperture radar satellite mission TanDEM-X provide valuable insights into glacier dynamics in those regions as the X-band radar is independent from clouds and illumination and can resolve elevation changes of large glacierized areas as well as individual glaciers. We use specifically generated and coregistered digital elevation models (DEM) from repeated TanDEM-X data takes to derive glacier elevation changes between 2010 and 2020.

For the Arctic regions, we already calculated elevation changes for the Russian Arctic archipelagos from TanDEM-X acquisitions (2000-2017). Currently, we are preparing similar TanDEM-X DEM differences for Arctic glaciers outside the Greenland ice sheet (Svalbard, Iceland, Alaska, Canadian Arctic, Scandinavia and North Asia). In contrast to the wide and smooth areas of the East and West Antarctic ice sheets, the steep topography of the Antarctic Peninsula strongly limits the application of altimeter data for accurately quantifying glacier mass changes. Therefore, we computed glacier mass changes along the Antarctic Peninsula by means of TanDEM-X data.

Additionally, measurements of the IceSAT2 laser altimeter will be integrated in the analysis to improve the estimation of radar signal penetration into snow and firn and thereby reduce the elevation change and mass balance uncertainties.

How to cite: Sommer, C., Seehaus, T., Sochor, L., Malz, P., and Braun, M.: The potential of TanDEM-X repeat acquisitions to monitor elevation and mass changes of Arctic and Antarctic glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12383,, 2021.

Caitlyn Florentine

The current global Randolph Glacier Inventory (RGI V6) minimum area cutoff is 0.01 km2. Including features this small empowers comprehensive assessments of global glacier water resources. It also enables high-resolution glacier hindcasts, ensuring that sites where modern glacier extent is now diminutive are charted and not overlooked. Yet the automated and manual mapping techniques used to generate RGI glacier outlines do not necessarily discriminate based on ice motion. There is currently no RGI mask that discerns between glaciers that likely still deform under their own weight (classic glacier) versus glaciers that are unlikely to satisfy this criterion (stagnant ice patch). Here is a highly simplified, data-driven attempt to develop a globally complete ice dynamic mask. Features are treated as simple slabs, with area given by the RGI database, order of magnitude thickness derived from volume-area power law scaling, and median surface slope derived from topography data (RGI-TOPO dataset, beta release). Driving stress is calculated using these inputs and assuming material density 900 kg m-3. This is repeated using varying elevation data sources, the globally complete consensus ice thickness estimate, and sparse direct ice thickness measurements (GlaThiDa), to explore driving stress sensitivity to different slab representations. Slabs with driving stress less than 105 Pa are interpreted as features where the ambient driving stress is insufficient to overcome the yield strength of ice. Uncertainty analysis and comparison against ice motion observations determines if these sub 105 Pa slab features reliably mask RGI glaciers that are no longer in motion. This approach serves as a first cut at developing a reproducible, systematic way of discerning between classic glaciers (bodies of ice that move) versus other cryosphere features. This may enhance consistency across technical analyses within the glaciological research community and science communication with policy makers.

How to cite: Florentine, C.: What is a Glacier? Assessing Ice Dynamic Thresholds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13629,, 2021.

Livia Jakob, Noel Gourmelen, and Johanna Kauffert

Glaciers are currently experiencing the largest land-ice imbalance and are the largest contributor to sea level rise after ocean thermal expansion, contributing ~30% to sea level budget. Global monitoring of these regions remains a challenging task since global estimates rely on a variety of observations and models to achieve the required spatial and temporal coverage, and significant differences remain between current estimates. Here we report, for the first time, the application of radar altimetry to retrieve spatially and temporally resolved elevation and mass changes of glaciers on a global scale. We apply interferometric swath altimetry to CryoSat-2 data acquired between 2010 and 2020 over all large mountain glacier regions and provide monthly and annual time series of glacier mass loss for each region, together with linear mass losses. We report ubiquitous and sustained ice loss ranging from 82.3 ± 6.3 Gt yr−1 in Alaska, to 3.4 ± 2.5 Gt yr−1 for the Antarctica Periphery. While there is a considerable spatial and temporal variability in imbalance, reflecting the complexity of regional atmospheric and oceanic forcing and of glacier forcing, the global glacier trend is remarkably sustained over this period. Globally, glaciers have lost a combined mean of 275 ± 15 Gt yr−1 between 2010 and 2020 contributing 0.76 ± 0.5 mm yr−1 to global Sea Level Rise.

How to cite: Jakob, L., Gourmelen, N., and Kauffert, J.: Global and monthly glacier mass balance from radar altimetry from 2010 to 2020, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13679,, 2021.

Loris Compagno, Sarah Eggs, Matthias Huss, Harry Zekollari, and Daniel Farinotti

With the Paris Agreement, leaders of the world have recognized the urgency of limiting ongoing, anthropogenic climate change. In preparation of the upcoming 26th UN Climate Change Conference of the Parties, discussions have been focusing on the difference of limiting the increase in global average temperatures below 1.0, 1.5, or 2.0°C compared to pre-industrial levels. Here, we assess the impacts that such different scenarios would have on both the future evolution of glaciers in the European Alps and the water resources they provide. We force the combined glacier mass balance and ice flow model GloGEMflow with climate projections from Coupled Model Intercomparison Project Phase 6 (CMIP6), and compute the area and volume evolution of all 3926 glaciers of the European Alps for the period 1990 to 2100. Our results show that the different temperature targets have important implications for the predicted changes: in a +1.0°C scenario, glaciers in the European Alpsare  projected to lose 44 ± 21 % of their 2020 ice volume; 68 ± 12 % in a +1.5 °C scenario; while 81 ± 8% in a +2.0°C scenario. The changes in glacier volume will strongly impact the water yield from presently-glacierized catchments, with 2080-2100 yearly average runoffs decreasing by 25 ± 6% (for a global warming of +1.0°C), 32 ± 8%, (+1.5°C) and 36 ± 10% (+2.0°C) when compared to 2000-2020 levels. Changes in peak runoff -- anticipated to occur 1 to 2 months earlier by the end of the century than it does today -- will be even more pronounced, with reductions of 23 ± 15 %, 29 ± 14 %, and 37 ± 15 % in the three warming scenarios, respectively.

How to cite: Compagno, L., Eggs, S., Huss, M., Zekollari, H., and Farinotti, D.: Why 0.5°C matter for the future evolution of Alpine glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14637,, 2021.

Andreas Vieli

Glacier surges periodically move ice masses to lower elevations and hence produce dynamic patterns of substantial thinning and thickening, but the net mass change over a typical time period of elevation change assessment of a few years to decades is not obvious.  Surging glaciers may therefore affect regional scale elevation change assessments as acquired from differencing of remotely sensed elevations, as for example for the observed Karakoram mass gain anomaly.

In this study I synthetically model glacier surges for a range of glacier sizes (slopes, thicknesses) and investigate the impact on the surface elevation change and total mass change for a typical range of surge durations, intensities and periods.

When keeping the climate forcing constant I find that the mean glacier elevation (or volume) is almost symmetric around the surge phase. Hence, when sampling elevation change over a large population of glaciers with randomly occurring surges there is little impact on the detected average elevation changes over all glaciers. The exceptions are steep glaciers which produce very short advance phases and much more extended phases of mass recovery. When sampling elevation change over a couple of years to decades, it is therefore much more likely to detect a thickening and therefore the population mean is biased to positive elevation change values.

When assessing mean elevation change on a regional scale, usually one fixed glacier outline is chosen for masking the data. However, for surging glaciers the extent can undergo large fluctuations. I therefore further assess the mean elevation change for glaciers extent masks that are varying between the maximum and minimum values of a surge. Despite a constant climate, the mean elevation change turns out to be increasingly biased towards detecting a thickening signal the further upstream the glacier extent is taken. This implies that for minimizing this thickening bias from glacier surges in assessing regional elevation change, glacier outline masks from their most extensive extents should be used.

Further modelling experiment showed that, the results are still valid when prescribing a variable climate forcing, but the surging effect is slightly subdued.  

How to cite: Vieli, A.: Numerical modelling assessment of glacier surge impact on observed elevation change signals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14874,, 2021.

Guðfinna Aðalgeirsdóttir, Eyjólfur Magnússon, Finnur Pálsson, Thorsteinn Thorsteinsson, Joaquín Belart, Tómas Jóhannesson, Hrafnhildur Hannesdóttir, Oddur Sigurðsson, Andri Gunnarsson, Bergur Einarsson, Etienne Berthier, Louise Schmidt, Hannes Haraldsson, and Helgi Björnsson

The volume of glaciers in Iceland (∼3,400 km3 in 2019) corresponds to about 9 mm of potential global sea level rise. In this study, observations from 98.7% of glacier covered areas in Iceland (in 2019) are used to construct a record of mass change of Icelandic glaciers since the end of the 19th century i.e. the end of the Little Ice Age (LIA) in Iceland. Glaciological (in situ) mass-balance measurements have been conducted on Vatnajökull, Langjökull, and Hofsjökull since the glaciological years 1991/92, 1996/97, and 1987/88, respectively. The combined record shows a total mass change of −540 ± 130 Gt (−4.2 ± 1.0 Gt a−1 on average) during the study period (1890/91 to 2018/19). This mass loss corresponds to 1.50 ± 0.36 mm sea level equivalent or 16 ± 4% of mass stored in Icelandic glaciers around 1890. Almost half of the total mass change occurred in 1994/95 to 2018/19, or −240 ± 20 Gt (−9.6 ± 0.8 Gt a−1 on average), with most rapid loss in 1994/95 to 2009/10 (mass change rate −11.6 ± 0.8 Gt a−1). During the relatively warm period 1930/31–1949/50, mass loss rates were probably close to those observed since 1994, and in the colder period 1980/81–1993/94, the glaciers gained mass at a rate of 1.5 ± 1.0 Gt a−1. For other periods of this study, the glaciers were either close to equilibrium or experienced mild loss rates. Comparison of our results with WGMS time series (Zemp et al., 2019) shows that the interannual variability is generally well captured by both data sets, but some details are not; for example, the large ice melt due to the Gjálp eruption in October 1996 and the non-surface mass balance are not included by WGMS data set. Our time seris is within the large uncertainty range of the GRACE record (Wouters et al., 2019) that has some years (e.g., 2006/07 and 2010/11) with more negative mass change, and others (e.g., 2005/06, 2011/12, and 2013/14) with less negative mass change than our estimates.

How to cite: Aðalgeirsdóttir, G., Magnússon, E., Pálsson, F., Thorsteinsson, T., Belart, J., Jóhannesson, T., Hannesdóttir, H., Sigurðsson, O., Gunnarsson, A., Einarsson, B., Berthier, E., Schmidt, L., Haraldsson, H., and Björnsson, H.: Glacier Changes in Iceland From ∼1890 to 2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15926,, 2021.