CR2.2

Triggered by climate change, glaciers are retreating world-wide at alarming rates. Since glacier melt can contribute significant proportions to hydrological catchment runoff, it is important to know how much meltwater glaciers can still release under decreasing ice volumes. For a better water resources management, a near real-time mass balance estimate would thus be desirable. On short time scales, glacier mass balance models are usually uncertain though, and they rely heavily on field data for calibration and validation. Because acquiring field data is resource-intensive, most studies rely exclusively on annual or seasonal data sets.

To provide an improved data basis for near-real time analyses produced within the CRAMPON project (Cryospheric Monitoring and Prediction Online), we aim at measuring glacier point ablation automatically, remotely and with high temporal resolution. For this purpose, we have equipped nine ablation stakes on Rhonegletscher, Grosser Aletschgletscher, Findelengletscher and Glacier de la Plaine Morte, Switzerland, with an additional setup: attached to each ablation stake, another aluminum stake construction holds a solar-powered camera at about 1m distance. As the ice surface melts, the camera slides down the ablation stake, takes RGB images of the bottom 50cm at 20min intervals, and sends the images to a server. Colored tape markers of known width and spacing serve as a scale reference on the stake. The total sequence of markers using eight different colors is shuffled to allow for a unique identification of sub-sequences of four markers.

By means of computer vision, the distance of the ablation stake top from the ice surface is obtained automatically: the stake is identified by finding collinear points of high color saturation on an image, i.e. the tape markers. The base point at the ice surface is given, because it has a fixed relative position to the camera. Individual markers are identified by their color, while the color sub-sequences provide the total position on the stake. A pixel-to-metric scale is calculated for each image from the known marker tape width and spacing, which also accounts for the perspective skewness of the stake. A reading uncertainty estimate of 2mm is derived from noise in the scale calculation. This estimate includes the quality of the detected marker bounds, image pixel size and the precision of the actual marker positions as error sources. Images with bad weather conditions are rejected by the processing.

The so-obtained ice melt time series between subsequent image pairs is aggregated to daily values. The results show good agreement with manual readings. In addition to the suggested image processing, we discuss two alternative approaches: by detecting tape markers through a template matching and tracking their location on the images over time, the alternatives avoid the reconstruction of the stake top position while being more sensitive to longer data gaps. We conclude that the presented setup is well-suited to automatically and remotely determine real-time ablation rates with low effort.

How to cite: Sold, L., Landmann, J. M., Borner, J., Cremona, A., Ogier, C., Huss, M., and Farinotti, D.: Automated real-time ice ablation readings using in situ cameras and computer vision techniques, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7663, https://doi.org/10.5194/egusphere-egu21-7663, 2021.

Greenland’s tidewater glaciers (TWG) have been retreating since the mid-1990s, contributing to mass loss from the Greenland Ice Sheet and sea level rise. Satellite imagery has been widely used to investigate TWG behaviour and determine the response of TWGs to climate. However, multi-day revisit times make it difficult to determine short-term processes such as calving and shorter-term velocity changes that may condition this. 

Here we present velocity, calving and proglacial plume data derived from hourly time-lapse images of Narsap Sermia, SW Greenland for the period July 2017 to June 2020 (n=13,513). Raw images were orthorectified using the Image GeoRectification And Feature Tracking toolbox (ImGRAFT; Messerli & Grinsted, 2015) using a smoothed ArcticDEM tile from 2016 (RMSE=44.4px). TWG flow velocities were determined using ImGRAFT feature tracking, with post-processing adjusting for varying time intervals between image acquisitions (if >1 hour) and removing outliers (>x2 mean). The high temporal resolution of the imagery also enabled the manual mapping of proglacial plume sizes from the orthorectified images and the recording of individual calving events by visually comparing images.

Results show a total retreat of approximately 700 m, with a general velocity increase from ~15 m/d to ~20 m/d over the investigated time period and highly variable hourly velocities (±12m/d). The number of calving events and plume sizes remain relatively stable from year to year throughout the observation period. However, later in the record plumes appear earlier in the year and the size of calved icebergs increases significantly, which suggests a change in calving behaviour. 

How to cite: Fahrner, D., Lea, J., Brough, S., and Abermann, J.: Using sub-daily timelapse imagery to investigate the behaviour of Narsap Sermia, SW Greenland., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7792, https://doi.org/10.5194/egusphere-egu21-7792, 2021.

Continuous global monitoring of glacier elevation change over decadal timescales is difficult to establish. Dedicated stereoscopic satellite missions are scarce and had, up to recently, limited spatial coverage. By contrast, observations from monoscopic satellites providing continuous global coverage extending for several decades backwards in time, is readily available. Therefore, we explore the potential of this type of imagery for extracting elevation change. This is done through tracking of moving shadows, which is a new and simple technique we call photohypsometry. The known sun angles and clear shadow patterns on the glacier surface, establish a simple trigonometric relationship, enabling the extraction of elevation change. 

Here we showcase the methodology on Red Glacier, a glacier situated on the Eastern flank of Iliamna volcano, Alaska. A tributary of this glacier has fast surface speed in its snout, slightly shifting lateral moraines, but no known surge history. Shadow from neighboring mountain ridges cast on the accumulation region of this glacier, so a clear time-series can be constructed from Sentinel-2 imagery.

This example highlights the potential of this technique. While the coverage of topographic information does not cover the whole glacial basin, it can complement other data sources. It is especially suited for small mountain glaciers and thrives in brightly reflecting snow-covered accumulation areas.

How to cite: Altena, B., Nattino, F., Ku, O., Grootes, M., Georgievska, S., Dzigan, Y., and Wouters, B.: Topographic elevation change through tracking shadow cast from mountain ridges. Showcasing Red Glacier, Mt. Iliamna., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10774, https://doi.org/10.5194/egusphere-egu21-10774, 2021.

Glaciological phenomena can have a strong impact on human activities in terms of hazards and freshwater supply. Therefore, scientific observation and continuous monitoring are fundamental to investigate their current state and recent evolution. Strong efforts in this field have been spent in the Grandes Jorasses massif (Mont Blanc area), where several break-offs and avalanches from the Planpincieux Glacier and the Whymper Serac (Grandes Jorasses Massif) threatened the Planpincieux hamlet in the past. In the last decade, multiple close-range remote sensing surveys have been conducted to study the glaciers.

Two time-lapse cameras monitor the Planpincieux Glacier since 2013. Its surface kinematics is measured with digital image correlation. Image analysis techniques allowed at classifying different instability processes that cause break-offs and at estimating their volume. The investigation revealed possible break-off precursors and a monotonic relationship between glacier velocity and break-off volume, which might help for risk evaluation.

A robotised total station monitors the Whymper Serac since 2009. The extreme high-mountain conditions force to replace periodically the stakes of the prism network that are lost.

In addition to these permanent monitoring systems, five campaigns with different commercial terrestrial interferometric radars have been conducted between 2013 and 2019. In 2020, two terrestrial GBSAR were installed for the improvement of the monitoring network of both glaciers. The adopted monitoring network is also composed by a Doppler radar that controls the potential detachment of ice blocks from the frontal part of the Planpincieux glacier. Besides, helicopter-borne LiDAR, terrestrial laser scanner and structure from motion applied to photo mosaics acquired by helicopter and UAV provided a dense series of high-resolution DTMs. Finally, new helicopter ground-penetrating radar campaigns were conducted in 2020 to evaluate the Planpincieux and Grandes Jorasses glaciers' thickness.

The survey activity conducted in the Grandes Jorasses area in the last decade is probably one of the most variegated in the European Alps. Thereby, this area has become an open-air laboratory for experimenting with new technological or methodological solutions for glaciological close-range remote sensing monitoring which might be applicable in other contexts.

How to cite: Giordan, D. and Fabrizio, T.: The open-air laboratory of the Grandes Jorasses glaciers. An opportunity for developing close-range remote sensing monitoring systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10675, https://doi.org/10.5194/egusphere-egu21-10675, 2021.

Mass balance observations are very useful to assess climate change in different regions of the world. As opposed to glacier-wide mass balances, which are influenced by the dynamic response of each glacier, point mass-balances provide a direct climatic signal that depends on surface accumulation and ablation only. Unfortunately, major efforts are required to conduct in situ measurements on glaciers. Here, we propose a new approach that determines point surface mass balances from remote sensing observations. We call this balance the geodetic point surface mass balance. From observations and modelling performed on Argentière and Mer de Glace glaciers over the last decade, we show that the vertical ice flow velocity changes are small in areas of low bedrock slope. Therefore, assuming constant vertical velocities in time for such areas and provided that the vertical velocities have been measured for at least one year in the past, our method can be used to reconstruct annual point surface mass balances from surface elevations and horizontal velocities alone. We demonstrate that the annual point surface mass balances can be reconstructed with an accuracy of about 0.3 m w.e. a^-1 using the vertical velocities observed over the previous years and data from Unmanned Aerial Vehicle images. Given the recent improvements of satellite sensors, it should be possible to apply this method to high spatial resolution satellite images as well.

How to cite: Vincent, C., Cusicanqui, D., Jourdain, B., Laarman, O., Six, D., Gilbert, A., Walpersdorf, A., Rabatel, A., Piard, L., Gimbert, F., Gagliardini, O., Peyaud, V., Arnaud, L., Thibert, E., Brun, F., and Nanni, U.: Geodetic point surface mass balances: A new approach to determine point surface mass balances on glaciers from remote sensing measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9843, https://doi.org/10.5194/egusphere-egu21-9843, 2021.

Interrelationships among mass balance, meteorology, discharge, and surface velocity on Chhota Shigri Glacier over 2002-2019 using in-situ measurements

Arindan MANDAL¹, AL. RAMANATHAN^1*, Mohd. Farooq AZAM², Thupstan ANGCHUK¹, Mohd. SOHEB¹, Naveen KUMAR¹, Jose George POTTAKKAL³, Sarvagya VATSAL¹, Somdutta MISHRA¹, Virendra Bahadur SINGH^1,4

^*Corresponding author email: alrjnu@gmail.com

The Himalayan glaciers contribute significantly to regional water resources. However, limited field observations restrict our understanding of glacier dynamics and behavior. Here, we investigated the long-term in-situ mass balance, meteorology, ice velocity, and discharge of the Chhota Shigri Glacier over the past two decades. With 17 years of uninterrupted glacier-wide mass balance datasets, Chhota Shigri Glacier is one of the most studied glaciers in the Hindu-Kush Himalayan region in terms of mass balance record. The mean annual glacier-wide mass balance was negative, -0.46±0.40 m w.e. a^-1 during 2002-2019 corresponding to a cumulative wastage of about -8 m w.e. Mean winter mass balance was 1.15 m w.e. a^-1 and summer mass balance was -1.35 m w.e. a^-1 over 2009-2019. Surface ice velocity has decreased on average by 25-42% in the lower and middle ablation zone (below 4700 m a.s.l.) since 2003; however, no substantial change was observed at higher altitudes. The decrease in velocity suggests that the glacier is adjusting its flow in response to negative mass balance. The summer discharge begins to rise from May and peaks in July, with a contribution of 43%, followed by 38% and 19% in August and September, respectively. The discharge pattern closely follows the air temperature. The long-term observation on the Chhota Shigri — a benchmark — glacier, shows a mass wastage that corresponds to the glacier’s slowdown in the past two decades.

How to cite: Alagappan(AL), R., Mandal, A., Mohd, A. F., Angchuk, T., Mohd, S., Kumar, N., Pottakkal, J. G., Vatsal, S., Mishra, S., and singh, V. B.: Interrelationships among mass balance, meteorology, discharge, and surface velocity on Chhota Shigri Glacier over 2002-2019 using in-situ measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11598, https://doi.org/10.5194/egusphere-egu21-11598, 2021.

Glaciers are a key indicator of climate change. Since the second half of the 20th century several glaciers in Antarctica have retreated. In situ measurements of glacier mass balance in the Antarctic Peninsula and its surrounding islands are very scarce because this area is inaccessible due to rough terrain and inhospitable atmospheric conditions, but there is a necessity in study peripheral glaciers dynamics to know their future contribution to sea level rise. To fill this gap, remote sensing is an alternative tool to enable timely monitoring of dynamic glaciers and quantifying spatial-temporal changes. Here we combine remote sensing (satellite imaginary and aerial photos) and in situ measurements to calculate mass balance for the Znosko glacier (King George Island, Antarctic Peninsula) and compare the accuracy of this methods. Two field campaigns were carried out during the XXVI and XXVII Peruvian Antarctic Operation (austral summer 2018/19 and 2019/20). 19 stakes were fixed on the glacier surface, in situ mass balance data were collected from yearly stake measurements. Also, digital elevation models were generated through aerial photogrammetry and auxiliary data from the ICESat-2 mission were included into the analysis.  We find that mass balances estimated with these methods are consistent and confirm the mass loss (heterogeneous pattern between accumulation and ablation zone) and retreat of Znosko glacier. We illustrate how participatory mapping (interdisciplinary team) can complement initial remote sensing land cover classification and assist ground checks.

How to cite: Bello, C., Suarez, W., Brondi, F., and Gonzales, G.: Mass balance study of the Znosko glacier, Antarctica, using remote sensing and in situ measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13732, https://doi.org/10.5194/egusphere-egu21-13732, 2021.

The Antarctic Peninsula ice sheet is an important contributor to sea-level rise and the glaciers in its peripheral islands have a large potential to increase their contribution under a warming climate. This region has undergone a complex history of climate change during recent decades, which justifies a close monitoring of their glaciers. The South Shetland Islands (SSI) is one of the northernmost archipelagos in this region, but it is lacking a geodetic mass balance (GMB) calculation for the entire archipelago. We have estimated the GMB of the SSI over a 3-4 years period within 2013-2017 (depending on the data availability for each island). Our estimation is based on remotely-sensed multispectral and interferometric SAR data covering 96% of the glacierized areas of the islands considered in our study, and 73% of the total glacierized area of the SSI archipelago (Elephant, Clarence and Smith Islands were excluded due to overly large slopes for SAR or limited input data). Our Results show a close-to-balance overall status during the analyzed period, with specific mass balances ranging from -0.680±0.071 to 0.209±0.025 m w.e. a^-1 on Low and Livingston islands, respectively. The average specific mass balance for the whole area is -0.064±0.015 m w.e. a^-1, representing an ice mass loss of 0.144±0.035 Gt a^-1. This result is consistent with the cooling trend observed in the region between 1998 and 2017, and with the mass balance estimates by the glaciological method performed in various glaciers in the AP region (and the SSI in particular).

How to cite: Shahateet, K., Seehaus, T., Navarro, F., and Braun, M.: First geodetic mass balance estimate of the bulk of the South Shetland Islands ice caps, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2758, https://doi.org/10.5194/egusphere-egu21-2758, 2021.

Knowing the ice thickness distribution of glaciers and ice caps is of critical importance for a number of studies. However, since measuring ice thickness directly is difficult and time consuming, the availability of such information is generally scarce. Here, we present results from the Second Phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX2) which had a two-fold objective. First, it aimed at characterizing the capability of numerical models to use sparse thickness measurements to their advantage. Second, it aimed at identifying possible strategies for maximizing the information content gained through direct ice thickness surveys.

The experiment was designed around 23 test cases including both real-world and synthetic glaciers, and comprised a set of 16 different experiments per test case simulating different scenarios of data availability. Based on a total of 2,544 individual solutions submitted by 13 different models, our results show that for locations without direct measurements, the ice thickness can be predicted with typical deviations in the order of 16% of the mean ice thickness. Despite large scatter, even limited sets of ice thickness observations are found to be effective in constraining the glacier total volume, particularly when the thickest part of a glacier is surveyed. Other spatial distributions of the ice thickness observations have only a weak influence on the predicted thickness, although surveys restricted to the lowest glacier elevations often result in an underestimation of the glacier’s total volume. The response to the various scenarios of data availability is found to be specific to individual models, and while no single best approach emerges, an ensemble-approach based on a combination of models is shown to be beneficial in terms of accuracy and robustness.

How to cite: Farinotti, D. and the ITMIX2 consortium: Where shall we measure? Results from the second phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX2), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3944, https://doi.org/10.5194/egusphere-egu21-3944, 2021.

How to cite: Hartl, L., Helfricht, K., Stocker-Waldhuber, M., Seiser, B., and Fischer, A.: Clustering patterns of volume change to classify glacier states and fates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9402, https://doi.org/10.5194/egusphere-egu21-9402, 2021.

With increasing anthropogenic greenhouse gas emissions and corresponding global warming, glaciers in Switzerland are shrinking rapidly as in many mountain ranges on Earth. Repeated glacier inventories are a key task to monitor such glacier changes and provide detailed information on the extent of glaciation, and important parameters such as area, elevation range, slope, aspect etc. for a given point or a period in time. Here we present the new Swiss Glacier Inventory (SGI2016) that has been acquired based on high-resolution aerial imagery and digital elevation models in cooperation with the Federal Office of Topography (swisstopo) and Glacier Monitoring in Switzerland (GLAMOS), bringing together topological and glaciological knowhow. We define the process, workflow and required glaciological adaptations to compile a highly accurate glacier inventory based on the digital Swiss topographic landscape model (swissTLM^3D).

The SGI2016 provides glacier outlines (areas), supraglacial debris cover, ice divides and location points of all glaciers in Switzerland referring to the years 2013-2018, whereas most of the glacier outlines have been mapped based on aerial images acquired between 2015-2017 (75% in number and 87% in area), with the centre year 2016. The SGI2016 maps 1400 individual glacier entities with a total glacier surface area of 961 km² (whereof 11% / 104 km² are debris-covered) and constitutes the so far most detailed cartographic representation of glacier extent in Switzerland. Analysing the dependencies between topographic parameters and debris-cover fraction on the basis of individual glaciers reveals that short glaciers with a moderate mean slope and glaciers with a low median elevation tend to have high debris fractions. A change assessment between the SGI1973 and SGI2016 based on individual glacier entities affirms the largest relative area changes for small glaciers and for low-elevation glaciers, whereas the largest glaciers show small relative area changes, though large absolute changes. The analysis further indicates a tendency for glaciers with a high share of supraglacial debris to show larger relative area changes.

Despite of an observed strong glacier volume loss between 2010 and 2016, the total glacier surface area of the SGI2016 is somewhat larger than reported in the last Swiss glacier inventory SGI2010. Even though both inventories were created based on swisstopo aerial photographs, the additional data, tools, resources and methodologies used by the professional cartographers digitizing glacier outlines in 3D for the SGI2016, are able to explain the counter-intuitive difference between SGI2010 and SGI2016. A direct comparison of these two datasets is thus not meaningful, but an experiment where a representative glacier sample of the SGI2010 was re-assessed based on the approaches of the SGI2016 led to an upscaled total glacier surface area of 1010 km² for the Swiss Alps around 2010. This indicates an area loss of 49 km² between the two last Swiss glacier inventories. As swisstopo data products are and will be regularly updated, the SGI2016 is the first step towards a consistent and accurate data product of repeated glacier inventories in six-year time intervals that promises a high comparability for individual glaciers and glacier samples.

How to cite: Linsbauer, A., Huss, M., Hodel, E., Bauder, A., Fischer, M., Weidmann, Y., and Bärtschi, H.: The new Swiss Glacier Inventory SGI2016: a detailed cartographic representation of Swiss glacier extent and supraglacial debris-cover, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5873, https://doi.org/10.5194/egusphere-egu21-5873, 2021.

Long-term glacier monitoring in Switzerland has resulted in some of the longest and most complete data series globally. Point mass balance observations, starting in the 19th century, are the backbone of the monitoring as they represent the raw and original data demonstrating the response of surface accumulation and melt to changes in climate forcing. Some of these time series on Swiss glaciers provide over 100 years of continuous measurements.

In the past, the variety of sources of historic measurements has only been partially investigated and never been completely and systematically processed and documented. Therefore, a new format for a point mass balance database was developed that allows full traceability of all measurements back to their original source as well as indicators for the quality of the data and corresponding measuring uncertainties. All previously included data sources were transferred into the new data base format and the original sources were re-assessed to validate or correct the entries and identify metadata. Furthermore, newly investigated measurements were added to the data base. The sources of data include an extremely diverse field from over 140 years of measurements such as published reports or studies, unpublished documents from field projects, field notes, digital sources as well as metaknowledge of the observers. Currently, data series with complete metadata for about 60 individual glaciers are available, corresponding to almost 60.000 point observations, one third of which are newly added.

In addition to extending the data base, this project also allowed us to systematically and homogenously fill in missing information such as estimates of the surface elevation of the measurement points and snow/firn density.  In the past, these density values often had to be assumed without actual measurements but those assumptions could vary up to 20% within different projects and assumptions were rarely flagged as such. The newly added metadata now allows performing an analysis of all actually measured density values and a homogenous interpolation of missing values across all times series based on known values. Furthermore, a system to estimate uncertainties of the mass balance measurements based on the metadata was developed as the accuracy of measurements between different measuring techniques and projects with very differing scientific objectives over a time frame of 140 years can vary significantly and therefore needs to be assessed. This quality-checked and complete data base now permits the re-analysis of consistent time series of glacier-wide mass balance allowing further interpretation of the climate change impacts on Swiss glaciers.

How to cite: Geibel, L., Kurzböck, C., Huss, M., and Bauder, A.: Data Rescue and Homogenization of Historic Mass Balance Measurements on Swiss Glaciers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2959, https://doi.org/10.5194/egusphere-egu21-2959, 2021.

Pyrenean glaciers are one of the southernmost glaciers in Europe. These ice bodies have suffered a fast retreat in the last decades mainly caused by the temperature increase of the last century. Here, we use state of the art airborne techniques to present the most complete evaluation of glacier volume change from 2011 to 2020.

In 2011 the Spanish Geographical Institute covered the entire country with airborne LiDAR. The glacier topography on the Spanish side of the Pyrenees (and also several hundreds of meters beyond the French border) was retrieved between September and November, when snow cover was minimal. In autumn 2020, we used different Unmanned Aerial Vehicles to survey 17 out of the 19 Pyrenean glaciers. The images acquired in these flights were processed with Structure from Motion algorithms to reconstruct the Digital Surface Model (DSM) in 3D of the glacier surfaces and nearby terrain.

Differencing of the DSM in 2011 and 2020 reveals a drastic retreat and volume loss. The mean elevation drop is 7 m, some glaciers had losses of more than 12 m in average with a surface lowering of more than 20 m locally. The mean annual mass balance observed when considering the 2D projection of glaciers surface was -1.83 m w.e./yr. Taking into account the true glaciers extent from the 3D surface retrieved from the UAV observations, the annual mass balance decreases to -1.30 m w.e./yr. The difference between these mass balances highlights the impact that utilising close range remote sensing observations have, when compared to satellite acquisitions, to accurately observe glaciers evolution in steep mountain areas.

How to cite: Revuelto, J., Vidaller-Gayán, I., Izagirre, E., Rojas-Heredia, F. E., Alonso-González, E., Rico, I., Gascoin, S., Berthier, E., Rene, P., and López-Moreno, J. I.: Volume drop of Pyrenean Glaciers from 2011 to 2020 observed with airborne techniques; LiDAR and SfM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9294, https://doi.org/10.5194/egusphere-egu21-9294, 2021.

Andean glaciers are an important part of the water cycle of high elevation catchments and supply fresh water to large populations downstreams, especially during dry periods. They are experiencing dramatic mass loss due to a warming climate, and their catchments are among the most vulnerable. However, relatively few glaciers are monitored systematically due to accessibility and cost, limiting our understanding of mass accumulation and ablation rates. In this study, we estimated the decadal altitudinal mass balance of glaciers in the Maipo River Basin in central Chile and the Rio Santa Basin in the Cordillera Blanca in Peru for the periods of 2000-2009 and 2009-2018. We accomplished this by 1) correcting current ice thickness estimates for recent thinning, 2) deriving glacier velocities from Landsat data using the Glacier Image Velocimetry (GIV) toolbox, and 3) modelling ice flux divergence using the continuity approach to correct observed glacier thinning for flow. We validated the altitudinally-resolved mass balance with the few available observational datasets, then determined each domain’s equilibrium line altitude, accumulation area ratio, and ablation balance ratio for each period, which identifies the portion of annual ablation that is compensated by accumulation.

Our results highlight the influence of the Chilean ‘Mega-drought’ (2010-present) on glacier health in the Maipo River Basin, causing a dramatic reduction in glacier mass balance (decrease of 0.5 m w.e. a-1) below 5000 m a.s.l., raising the regional equilibrium line altitude from 4210 m a.s.l. during 2000-2009 to 4470 m a.s.l. ± 15 m during 2009-2018, and lowering accumulation area ratios from 0.65 to 0.55. In contrast, the Santa Basin glaciers showed very similar altitudinal mass balance patterns for both decades, with equilibrium line altitudes at ~5100 m a.s.l. and accumulation area ratios of ~0.5, indicating a basin already out of balance prior to 2000. 

Large populations rely on glaciers’ water supply in both basins and the two basins’ glaciers contrast in terms of water supply sustainability. In the Maipo Basin, glaciers experienced little mass change in the first period (ablation balance ratio of 1.01) and experienced only slightly unsustainable mass loss in the second period (ablation balance ratio of 0.9) despite the Megadrought. The ablation balance ratio for the Santa Basin was lower for both periods (0.75) indicating that these glaciers are moderately unhealthy despite their recent retreat, and water managers should expect further reductions in glacier water supply. Our results will help to constrain glacier models to understand the timing of glacier change for this data-sparse region.

How to cite: von Ah, F., Miles, E., Dussaillant, I., Shaw, T. E., Molnar, P., and Pellicciotti, F.: Decadal altitudinal glacier mass balance for the Maipo and Santa basins of South America, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12009, https://doi.org/10.5194/egusphere-egu21-12009, 2021.

Svalbard is famous for its numerous surge-type glaciers as well as for the harsh weather conditions of a highly maritime Arctic island, making regular observations of its glaciers challenging. However, the rapid changes of glacier geometry require a frequent update of their extent to perform accurate glacier-specific calculations such as their mass balance or contribution to sea level. The last inventory for Svalbard has been compiled by Nuth et al. (2013) from about 40 satellite scenes acquired by three different sensors (ASTER, Landsat, SPOT) on 30 unique days over a period of 10 years. Accordingly, any change assessment or other time dependent calculations are difficult to perform and a temporarily more consistent dataset is urgently required.

In this study we present the results of a new glacier inventory for Svalbard that has been derived from two Sentinel-2 swaths acquired for the main island within 3 days of 2017 and on 1 day in 2016 from Landsat 8 for Nordaustlandet. The images had overall very good snow conditions but in some regions late seasonal snow was hiding glaciers. Glacier mapping under local clouds in the very north and south could be performed by using further scenes from 2017 processed with GEE. We applied a simple red/SWIR band ratio to map clean ice and corrected wrong classifications (sea ice, lakes) or missing parts (debris cover) manually. New drainage divides and topographic parameters were derived from the ArcticDEM.

The new inventory counts 3136 glaciers >0.01 km² covering an area of 32,948 km². Of these, glaciers < 1 km² cover 1.3% of the area but nearly 44% of the number whereas glac-iers >10 km² cover 91% of the area and 10% by number. Compared to the previous inventory we have 1468 glaciers more and 2.5% area less. However, when excluding the 2025 glaciers <1 km², we only identified 1111 glaciers, i.e. 557 less than in the previous inventory. The differences are mostly due to newly considered entities, different drainage divides, glacier retreat and advance/surging. By excluding surge-type glaciers, a more meaningful determination of climate-related area changes can be performed. The presentation will discuss the differences of the new inventory to the RGI dataset, the specific glacier mapping challenges and our approach to solve them.

How to cite: Paul, F., Goerlich, F., and Rastner, P.: A new glacier inventory for Svalbard from Sentinel-2 and Landsat 8 for improved calculation of climate change impacts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14499, https://doi.org/10.5194/egusphere-egu21-14499, 2021.