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The panoramic cameras (PCs) on board Hexagon KH-9 (KH-9PC) satellite missions from 1971–1984 captured very high-resolution stereo imagery with up to 60 cm spatial resolution. This study explores the potential of this imagery for glacier mapping and change estimation. We assess KH-9PC imagery using data from the KH-9 mapping camera (KH-9MC), KH-4PC, and SPOT and Pléiades satellite imagery. The high resolution of KH-9PC leads to higher-quality DEMs, which better resolve the accumulation region of the glaciers in comparison to the KH-9MC. On stable terrain, KH-9PC DEMs achieve an elevation accuracy of

This research was funded by the European Space Agency Permafrost-CCI project (grant number 4000123681/18/I-NB). Rock glaciers are landforms related to permafrost creep that are sensitive to climate variability and change. Their spatial distribution and kinematic behaviour can be critical for managing water resources and geohazards in periglacial areas. Rock glaciers have been inventoried for decades worldwide, often without assessment of their kinematics. The availability of remote sensing data however makes the inclusion of kinematic information potentially feasible, but requires a common methodology in order to create homogeneous inventories. In this context, the International Permafrost Association (IPA) Action Group on rock glacier inventories and kinematics (2018-2023), with the support of the European Space Agency (ESA) Permafrost Climate Change Initiative (CCI) project, is defining standard guidelines for the inclusion of kinematic information within inventories. Here, we demonstrate the feasibility of applying common rules proposed by the Action Group in 11 regions worldwide. Spaceborne interferometric synthetic aperture radar (InSAR) was used to characterise identifiable moving areas related to rock glaciers, applying a manual and a semi-automated approach. Subsequently, these areas were used to assign kinematic information to rock glaciers in existing or newly compiled inventories. More than 5000 moving areas and more than 3600 rock glaciers were classified according to their kinematics. The method and the preliminary results were analysed. We identified drawbacks related to the intrinsic limitations of InSAR and to various applied strategies regarding the integration of non-moving rock glaciers in some investigated regions. This is the first internationally coordinated work that incorporates kinematic attributes within rock glacier inventories at a global scale. The results show the value of designing standardised inventorying procedures for periglacial geomorphology. Copyright: © 2022 Aldo Bertone et al. Publisher PDF

Multi-temporal glacier inventories provide key information about the glaciers, their characteristics, and changes and are inevitable for glacier modelling and investigating geodetic mass changes. However, to date, no consistent multi-temporal glacier inventory for the whole of the Karakoram exists, negatively affecting the monitoring of spatio-temporal variations in glaciers' geometric parameters and their related applications. We used a semi-automatic method combining automatic segmentation and manual correction and produced a multi-temporal Karakoram glacier inventory (KGI) compiled from Landsat TM/ETM+/OLI (Thematic Mapper, Enhanced Thematic Mapper Plus, and Operational Land Imager) images for the 1990s, 2000s, 2010s, and 2020s. Our assessments using independent multiple digitisation of 37 glaciers show that the KGI is sufficiently accurate, with an overall uncertainty of ±3.68 %. We also performed uncertainty evaluation for the contiguous glacier polygons using a buffer of half a pixel, which resulted in an average mapping uncertainty of ±5.21 %. We calculated more than 20 attributes for each glacier, including coordinates, area, supraglacial debris area, date information, and topographic parameters derived from the ASTER GDEM (Advanced Spaceborne Thermal Emission and Reflection Radiometer global digital elevation model). According to KGI-2020s, approximately 10 500 alpine glaciers (>0.01 km2 each) cover an area of 22 510±828 km2 of which 10.18±0.38 % (2290±84 km2) is covered by supraglacial debris. Over the past 3 decades, the glaciers experienced a loss of clean ice and/or snow area but a gain in supraglacial debris. Supraglacial debris cover has increased by 17.63±1.44 % (343.30±27.95 km2), while non-debris-covered glaciers decreased by 1.56±0.24 % (319.85±49.92 km2). The total glacier area was relatively stable and showed only a slight insignificant increase of 23.45±28.85 km2 (0.10±0.13 %). The glacier area has declined by 3.27±0.24 % in the eastern Karakoram, while the glacier area slightly increased in central (0.65±0.10 %) and western Karakoram (1.26±0.11 %). Supraglacial debris has increased over the whole of Karakoram, especially in areas above 4200 m a.s.l. (above sea level), showing an upward shift. The glacier area changes were characterised by strong spatial heterogeneity, influenced by surging and advancing glaciers. However, due to global warming, the glaciers are on average retreating. This is in particular true for small and debris-free glaciers. The multi-temporal KGI data are available at the National Cryosphere Desert Data Center of China: https://doi.org/10.12072/ncdc.glacier.db2386.2022 (F. Xie et al., 2022).

Glaciers are crucial sources of freshwater in particular for the arid lowlands surrounding High Mountain Asia. In order to better constrain glacio-hydrological models, annual, or even better, seasonal information about glacier mass changes is highly beneficial. In this study, we test the suitability of very high-resolution Pleiades DEMs to measure glacier-wide mass balance at annual and seasonal scales in two regions of High Mountain Asia (Muztagh Ata in Eastern Pamir and parts of Western Nyainqêntanglha, South-central Tibetan Plateau), where recent estimates have shown contrasting glacier behaviour. We find that the average annual mass balance in Muztagh Ata between 2020 and 2022 was -0.11 ±0.21 m w.e. a-1, suggesting the continuation of a recent phase of slight mass loss following a prolonged period of balanced mass budgets previously observed. The mean annual mass balance in Western Nyainqêntanglha for the same period was highly negative (-0.60 ±0.15 m w.e. a-1 on average), suggesting increased mass loss rates. The 2022 winter (+0.21 ±0.24 m w.e.) and summer (-0.31 ±0.15 m w.e.) mass budgets in Muztag Ata and Western Nyainqêntanglha (-0.04 ±0.27 m w.e. [winter]; -0.66 ±0.07 m w.e. [summer]) suggest winter and summer accumulation-type regimes, respectively. We support our findings by implementing a Sentinel-1–based Glacier Index to identify the firn and wet snow areas on glaciers and characterize accumulation type and demonstrate the potential of very high-resolution Pleiades data to monitor mass balance at short time scales and to improve our understanding of glacier accumulation regimes across High Mountain Asia.

Global warming-induced melting and thawing of the cryosphere are rapidly changing hydrogeomorphic processes and cryospheric hazards in high mountain areas worldwide. These processes and hazards include glacial retreat and collapses, permafrost thaw and associated landslides, rock-ice avalanches, debris flows, and outburst floods from glacier lakes and landslide-dammed lakes. The changing slope instability and extreme flood have accelerated landscape erosion and increased fluvial sediment loads. For example, the rivers in High Mountain Asia are becoming muddier due to increased suspended particulate matters from melting glaciers and thawing permafrost, likely degrading water quality as fine-grained sediment are easily bonded with organic carbon, phosphorus and most heavy metals (e.g., mercury, chromium, arsenic and lead). Importantly, numerous hydropower dams and reservoirs are under construction or planning in high-mountain areas worldwide such as in the Himalaya and Andes. The increasing amounts of mobilized sediment can fill up reservoirs, cause dam failure, and degrade power turbines, threatening the short-term safety and longer-term sustainability of these hydropower systems.In the future, we recommend forward-looking design and maintenance solutions that can help transition towards climate change-resilient high-quality water supply and hydropower systems in high-mountain areas. The specific suggestions include: (i) monitor the climate, glaciers and permafrost, glacial lakes, unstable slopes, discharge and sediment yields to better understand the cascading links between climate change, glacier retreat and hazards; (ii) predict future fluvial sediment loads, water quality and reservoir sedimentation in a changing climate and develop sustainable sediment management solutions; (iii) establish real-time early warning systems and enhance social awareness and drills, especially for in-construction dams to minimize human and infrastructure losses; (iv) enhance transboundary cooperation by establishing data-sharing schemes and adopting joint-operation strategies to better cope with hazards and optimise sediment flushing; and (v) promote the inclusion of indigenous and local knowledge in policy, governance, and management for water quality assessment and dam and reservoir construction.The major results of this study have been published online: Li, D., Lu, X., Walling, D. E., Zhang, T., Steiner, J. F., Wasson, R. J., ... & Bolch, T. (2022). High Mountain Asia hydropower systems threatened by climate-driven landscape instability. Nature Geoscience, 15(7), 520-530. https://doi.org/10.1038/s41561-022-00953-y

The Arctic tundra biome is large and difficult to access. Satellite monitoring is essential for observing changes in these areas, but in most cases the resolution of imagery is larger than typical vegetation patch sizes. NDVI greening trends have been observed in most parts of the Arctic since the 1980s. These trends can be explained by the expansion of vegetated areas, higher biological productivity and changing vegetation composition. Low to tall stature shrubs are changing the spectral reflectance characteristics of the overall tundra vegetation. In particular, the NIR wavelengths are affected, resulting in higher NDVI values.At the same time, soil erosion threatens parts of the tundra biome such as in Iceland. Soil erosion occurs due to biogeomorphological processes. Uncertainties remain in how these processes will adjust to a rapidly changing climate and to anthropogenic pressures such as grazing. This makes the future trajectory of these landscapes difficult to predict. Critical thresholds may exist in these landscapes, which if crossed, can lead to irreversible desertification. For these reasons, it’s important to be able to accurately assess the environmental state of these landscapes, especially the extent of soil erosion.Satellite observation of NDVI greening in areas undergoing shrub expansion could mask other trends, such as increasing levels of soil erosion. This is because typical satellite datasets used for tundra monitoring have resolutions in the order of 10s of m, which means that each pixel tends to include multiple different land cover types. At the level of a sensed pixel, higher NDVI values of shrubs could lead to a net positive NDVI trend, despite the eroded area increasing.To address this issue, we need to establish which spatial resolutions are appropriate for monitoring. We used a multi-scale study in a degraded tundra landscape in northern Iceland. Different satellite products from (PlanetScope, Sentinel-2, Landsat-8) were compared with 1.1 km2 multispectral UAV imagery collected in 2021. The very high-resolution UAV imagery (0.05 m resolution) is used to classify land cover and allows us to explore how the composition of different land cover classes affects the overall NDVI value of a satellite pixel (3 – 30 m resolution) at the same location.We find that for the same NDVI values in a satellite pixel, the UAV data reveals large variations in the degree of soil erosion. This can mainly be attributed to variability in the ratio of shrub cover to other vegetation cover, which alters the spectral signature of a pixel. This makes the interpretation of NDVI trends more difficult and stresses the importance of using an appropriate spatial resolution. Landsat-8 (30 m) revealed low accuracy in resolving tundra heterogeneity, while Sentinel-2 (10 m) and PlanetScope (3 m) showed significant improvements.This study highlights the importance of using the right spatial resolution when monitoring highly fragmented environments, and the need to consider that an increase in NDVI may not reflect an improvement in environmental state.

The highly glacierised eastern part of the Tibetan Plateau is the key source region of the five major rivers Yangtze, Yellow, Lancang-Mekong, Nu-Salween and Brahmaputra rivers. These exotic rivers are vital freshwater resources for more than one billion people downstream for their daily life, irrigation, industrial use, and hydropower. However, the glaciers have been receding during the last decades and are projected to further decline which will profoundly impact the water availability of these larger river systems. Although few studies have investigated glacier mass changes in these river basins since the 1970s, they are site and temporal specific and limited by data availability. Hence, knowledge of glacier mass changes is especially lacking for years prior to 2000. We therefore applied digital elevation models (DEMs) derived from large scale topographic maps based on aerial photogrammetry from the 1970s and 1980s and compared them to the SRTM DEM to provide a complete picture of mass change of glaciers in the region. The mass changes are presented on individual glacier bases with a resolution of 30 m and the grided (0.1° and 0.5°). Our database consists of 17444 glaciers with a total area of 17426 ± 523 km2. The annual mean mass loss of glaciers is -0.28 ± 0.15 m w.e. in the whole region. This is larger than the previous site-specific findings, the surface thinning increases on average from west to east along the Himalayas-Hengduan mountains with the largest thinning in the Salween basin. Comparisons between the topographic map-based DEMs and DEMs generated based on Hexagon KH-9 metric camera data for parts in the Himalayas demonstrate that our dataset provides a robust estimation of glacier mass changes. However, the uncertainty is high in high altitudes due to the saturation of aerial photos over low contrast areas like snow surface on a steep terrain. The dataset is well suited for supporting more detailed climatical and hydrological analyses and are available at https://doi.org/10.11888/Cryos.tpdc.272884 (Liu et al., 2022).

Glaciers are crucial sources of freshwater in particular for the arid lowlands surrounding High Mountain Asia. In order to better constrain glacio-hydrological models, annual, or even better, seasonal information about glacier mass changes is highly beneficial. In this study, we test the suitability of very high-resolution Pleiades DEMs to measure glacier-wide mass balance at annual and seasonal scales in two regions of High Mountain Asia (Muztagh Ata in Eastern Pamir and parts of Western Nyainqêntanglha, South-central Tibetan Plateau), where recent estimates have shown contrasting glacier behavior. We find that the average annual mass balance in Muztagh Ata between 2020 and 2022 was -0.11 ±0.21 m w.e. a-1, suggesting the continuation of a recent phase of slight mass loss following a prolonged period of balanced mass budgets previously observed. The mean annual mass balance in Western Nyainqêntanglha for the same period was highly negative (-0.60 ±0.15 m w.e. a-1 on average), suggesting increased mass loss rates. The 2022 winter (+0.21 ±0.24 m w.e.) and summer (-0.31 ±0.15 m w.e.) mass budgets in Muztag Ata and Western Nyainqêntanglha (-0.04 ±0.27 m w.e. [winter]; -0.66 ±0.07 m w.e. [summer]) suggest winter and summer accumulation-type regimes, respectively. We support our findings by implementing a Sentinel-1–based Glacier Index to identify the firn and wet snow areas on glaciers and characterize accumulation type. The good match between the geodetic and Glacier Index results demonstrates the potential of very high-resolution Pleiades data to monitor mass balance at short time scales and improves our understanding of glacier accumulation regimes across High Mountain Asia.

The field work at Satopanth Glacier was supported by SERB & DST, New Delhi (Grant No. SB/DGH-101/2015 and DST/CCP/NHC/158/2018), IMSc, Chennai and SAC-ISRO funded projects. Parts of the work were conducted in the framework of the project ‘Understanding and quantifying the transient dynamics and evolution of debris-covered glaciers’ funded by the Swiss National Science Foundation (Grant No. 200021-169775). Himalayan glaciers have been shrinking and losing mass rapidly since 1970s with an enhanced rate after 2000. The shrinkage is, however, quite heterogeneous and it is important to document individual glacier characteristics and their changes at the basin scale. We present an updated glacier inventory of the Upper Alaknanda Basin (UAB), Central Himalaya for the year 2020 and report area, debris cover and length changes for the periods 1994–2006 and 2006–2020 based on remote-sensing data. We identified 198 glaciers, comprising an area of 354.6 ± 8.5 km2, and classified them according to their size and morphology. The glaciers of the basin lost 4.2 ± 2.9% (0.16 ± 0.11% a−1) of their frontal area (from 368.6 ± 9.2 to 353.0 ± 5.3 km2) from 1994 to 2020. The average retreat rate was higher in the period 2006–2020 (13.3 ± 1.8 m a−1) in comparison to 1994–2006 (9.3 ± 1.9 m a−1). However, the area change rate was similar for the two periods (0.14 ± 0.27% a−1 for 1994–2006 and 0.16 ± 0.19% a−1 for 2006–2020). The debris-covered area has increased by 13.4 ± 4.4% from 1994 to 2020. A comparison with previous studies in UAB indicates consistent area loss of ~0.15% a−1 since the 1960s. Publisher PDF

Funding: This manuscript resulted from a Workshop in 2019 at the Senckenberg Research Institute and Natural History Museum Frankfurt, Germany, supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA20100300). J. Liu also thanks the support of the Henan Provincial Key Laboratory of Hydrosphere and Watershed Water Security. T. Ehlers thanks the California Institute of Technology Moore Distinguished Scholar Program for support in completing this manuscript during a sabbatical. J. Liu and T. Bolch thank the support from the Strategic Priority Research Program of the Chinese Academy of Sciences (grants no. XDA20060402, XDA20100300). We thank the German Science Foundation (DFG) for support of the TiP (Tibetan Plateau: Formation-Climate-Ecoystems) priority research program (SPP-1372) for initiating the collaborations that led to this manuscript. Interactions between the atmosphere, biosphere, cryosphere, hydrosphere, and geosphere are most active in the critical zone, a region extending from the tops of trees to the top of unweathered bedrock. Changes in one or more of these spheres can result in a cascade of changes throughout the system in ways that are often poorly understood. Here we investigate how past and present climate change have impacted permafrost, hydrology, and ecosystems on the Tibetan Plateau. We do this by compiling existing climate, hydrologic, cryosphere, biosphere, and geologic studies documenting change over decadal to glacial-interglacial timescales and longer. Our emphasis is on showing present-day trends in environmental change and how plateau ecosystems have largely flourished under warmer and wetter periods in the geologic past. We identify two future pathways that could lead to either a favorable greening or unfavorable degradation and desiccation of plateau ecosystems. Both paths are plausible given the available evidence. We contend that the key to which pathway future generations experience lies in what, if any, human intervention measures are implemented. We conclude with suggested management strategies that can be implemented to facilitate a future greening of the Tibetan Plateau. Publisher PDF

This study was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (XDA20100300) and the Swiss National Science Foundation (200021E 177652/1) within the framework of the DFG Research Unit GlobalCDA (FOR2630). The Corona KH-4 reconnaissance satellite missions acquired panoramic stereo imagery with high spatial resolution of 1.8–7.5m from 1962-1972. The potential of 800,000+ declassified Corona images has not been leveraged due to the complexities arising from handling of panoramic imaging geometry, film distortions and limited availability of the metadata required for georeferencing of the Corona imagery. This paper presents the Corona Stereo Pipeline (CoSP): A pipeline for processing of Corona KH-4 stereo panoramic imagery. CoSP utilizes deep learning based feature matcher SuperGlue to automatically match features point between Corona KH-4 images and recent satellite imagery to generate Ground Control Points (GCPs). To model the imaging geometry and the scanning motion of the panoramic KH-4 cameras, a rigorous camera model consisting of modified collinearity equations with time-dependent exterior orientation parameters is employed. Using the entire frame of the Corona image, bundle adjustment with well-distributed GCPs results in an average standard deviation or σ0 of less than two pixels. We evaluate fiducial marks on the Corona films and show that pre-processing the Corona images to compensate for film bending improves the 3D reconstruction accuracy. The distortion pattern of image residuals of GCPs and y-parallax in epipolar resampled images suggest that film distortions due to long-term storage likely cause systematic deviations of up to six pixels. Compared to the SRTM DEM, the Corona DEM computed using CoSP achieved a Normalized Median Absolute Deviation of elevation differences of ≈ 4m over an area of approx. 4000km2 after a tile-based fine coregistration of the DEMs. We further assess CoSP on complex scenes involving high relief and glacierized terrain and show that the resulting DEMs can be used to compute long-term glacier elevation changes over large areas. Postprint

High Mountain Asia (HMA) – the Tibetan Plateau and surrounding high Asian mountains – is now experiencing amplified climate change, glacier melt, and permafrost thaw. The rapid climate change and melting and thawing of the cryosphere are not only affecting the water cycle but also causing landscape instability and mountain hazards, potentially threatening over 2 billion people in the downstream river basins. Glacier retreat and permafrost thaw are accelerating associated with frequent rockfalls, landslides, and debris flows. Lake outburst floods from (pro)glacial- and landslide-dammed lakes have potential runout distances of hundreds of kilometers. Moreover, greater amounts of sediment are mobilized, and fluvial sediment fluxes are increasing. Such mountain landscape instability can be largely attributed to climate change and is threatening infrastructure and livelihoods. We suggest that policymakers and stakeholders in the Himalaya countries must be urgently and fundamentally aware of these increasing threats in a changing climate. Adaptation measures should be based on extensive and continual monitoring of the glaciers, permafrost, unstable paraglacial landscapes, and sediment transport, to better understand compound and cascading hazards.

The investigation of surging glaciers using remote sensing has recently seen a strong increase as freely available satellite data and digital elevation models (DEMs) can provide detailed information about surges that often take place in remote and inaccessible regions. Apart from analysing individual surges, satellite information is increasingly used to collect valuable data on surging glaciers. Related inventories have recently been published for several regions in High Mountain Asia including the Karakoram or parts of the Pamir and western Kunlun Shan, but information for the entire Pamir is solely available from a historic database listing about 80 glaciers with confirmed surges. Here we present an updated inventory of confirmed glacier surges for the Pamir that considers results from earlier studies and is largely based on a systematic analysis of Landsat image time series (1988 to 2018), very high-resolution imagery (Corona, Hexagon, Bing Maps, Google Earth) and DEM differences. Actively surging glaciers (e.g. with advancing termini) were identified from animations and flicker images and the typical elevation change patterns (lowering in an upper reservoir zone and thickening further down in a receiving zone). In total, we identified 206 spatially distinct surges within 186 glacier bodies mostly clustered in the northern and western part of the Pamir. Where possible, minimum and maximum glacier extents were digitised, but often interacting tributaries made a clear separation challenging. Most surging glaciers (n=70) are found in the larger size classes (>10 km2), but two of them are very small ( km2). We also found several surges where the length of the glacier increased by more than 100 %. The created datasets are available at: https://doi.org/10.1594/PANGAEA.914150 (Goerlich et al., 2020).

This study was conducted within the project SuMaRiO (Sustainable Management of River Oases along the Tarim River; http://www.sumario.de/), funded by the German Federal Ministry of Education and Research (BMBF grants 01LL0918J, 01LL0918I and 01LL0918B). T. Bolch acknowledges funding by Deutsche Forschungsgemeinschaft (DFG, BO3199/2–1). Open Access funding enabled and organized by Projekt DEAL. Glacierised river catchments are highly sensitive to climate change, while large populations may depend on their water resources. The irrigation agriculture and the communities along the Tarim River, NW China, strongly depend on the discharge from the glacierised catchments surrounding the Taklamakan Desert. While recent increasing discharge has been beneficial for the agricultural sector, future runoff under climate change is uncertain. We assess three climate change scenarios by forcing two glacio-hydrological models with output of eight general circulation models. The models have different glaciological modelling approaches but were both calibrated to discharge and glacier mass balance observations. Projected changes in climate, glacier cover and river discharge are examined over the twenty-first century and generally point to warmer and wetter conditions. The model ensemble projects median temperature and precipitation increases of + 1.9–5.3 °C and + 9–24%, respectively, until the end of the century compared to the 1971–2000 reference period. Glacier area is projected to shrink by 15–73% (model medians, range over scenarios), depending on the catchment. River discharge is projected to first increase by about 20% in the Aksu River catchments with subsequent decreases of up to 20%. In contrast, discharge in the drier Hotan and Yarkant catchments is projected to increase by 15–60% towards the end of the century. The large uncertainties mainly relate to the climate model ensemble and the limited observations to constrain the glacio-hydrological models. Sustainable water resource management will be key to avert the risks associated with the projected changes and their uncertainties. Publisher PDF

GLIMS, Global Land Ice Measurements from Space, is an initiative that involves ~250 analysts from 34 countries and has the purpose of mapping all glaciers in the world (excluding the Greenland and Antarctic ice sheets) on a periodic basis. The GLIMS Glacier Database, which became an official product of the NASA NSIDC DAAC (Distributed Active Archive Center) in 2019, contains time series of glacier outlines from different data sources. Various parts or facies of glaciers are mapped, including the full glacier extent, debris-covered parts, internal rock outcrops, and glacial lakes. The Randolph Glacier Inventory (RGI) is a snapshot map of glaciers, with one outline per glacier, as close as possible to a target date.In the last year, GLIMS and the RGI working group have been working closely together to ingest new data into GLIMS and to improve GLIMS and RGI software tools. The goal is to improve data completeness and quality and to make the creation of the RGI smoother and more transparent (Maussion et al., EGU22-4484). New data include approximately 60,000 outlines from 14 regions in all parts of the Earth, with times ranging from the Little Ice Age to 2018. Software improvements include more quality-control checks and constraints, such as separating multi-polygons into individual ones. The presentation will provide an overview on the latest data additions and software developments in GLIMS and the synergy with RGI production.

Various interdisciplinary studies have shown substantial discrepancies between modeled and remotely sensed glacier surface elevation change.It is therefore crucial to better understand and quantify uncertainties associated to both methods. We design a probabilistic framework with the aim to filter outliers, fill data voids and estimate uncertainties in glacier surface elevation changes computed from Digital Elevation Model (DEM) differentiation. The technique is based on a Bayesian formulation of the DEM difference problem and specifically targets surging and debris-covered glaciers, both at glacier and regional scales. We first define a set of physically admissible surface elevation changes as an elevation-dependent probability density function.In a second step, terrain roughness is defined as the main descriptor for DEM uncertainty. Each surface elevation change pixel is a probability distribution. We present validation experiments in High Mountain Asia and show that the model produces results consistent with conventional DEM differencing, while avoiding the caveats of already existing methods. We further demonstrate that accounting for unstable glacier dynamics is crucial for accurate outlier filtering and robust uncertainty estimation. The technique can be applied to other types of remotely sensed glacier quantities (surface velocity etc.) and would provide more reliable characterization of uncertainty associated with changes in glacier mass and dynamics.

Numerical modelling studies examining the transient behaviour of debris-covered glaciers have typically varied either the equilibrium line altitude, which is a proxy for climate, or the rate of debris deposition. Since the rate of debris production from headwall erosion is believed to be an increasing function of temperature, a more faithful representation of debris-covered glacier evolution should include a coupling between debris source strength and climate.In this study, we examine the transient response of debris-covered glaciers to the combined effect of a warming climate and a related increasing debris source using a numerical model that couples ice flow with englacially transported debris. This allows for a debris melt-out concentration in the ablation zone that varies in time and space, depending on the evolving glacier dynamics and the debris deposition history.We find that debris-covered glaciers in a warming climate exhibit a complex transient response with aspects of both retreat and advance, though these distinct responses occur on different timescales. This suggests that the observed present-day retreat of debris-covered glaciers may be followed by an eventual advance despite a continued increase in global mean temperature.

The dependence of rock glaciers on permafrost and thus their sensitivity to climatic parameters makes the spatial distribution of these landforms very important for hydrological and climate changes reasons. Inventories of rock glaciers have been produced for decades worldwide, often without an assessment of their kinematics; the availability of remote sensing data makes the inclusion of kinematic information potentially feasible, but the absence of a common methodology makes it challenging to create homogeneous inventories. In this context, the IPA Action Group on rock glacier inventories and kinematics (2018–2023), with the support of the ESA Permafrost_CCI project, is promoting the definition of standard guidelines for the inclusion of kinematic information within inventories. Here, we test the feasibility of applying common rules proposed by the Action Group in eleven regions worldwide. Satellite interferometry is used to characterize identifiable areas with slope movements related to rock glaciers; subsequently, these areas are used to assign kinematic information to rock glaciers in existing or newly compiled inventories. More than 5,000 slope movements and more than 3,600 rock glaciers are classified according to their kinematics. The analyzes conducted on the method and on the preliminary results show small irregularities related to the detection capacity of interferometry and to lack of rock glaciers without detectable movements in some regions investigated. This is the first internationally coordinated effort of rock glacier inventories. We demonstrate the feasibility of applying common rules to implement kinematic attributes within inventories at a global scale, despite the various regions and intensive manual effort.

Funding to support this research from the University of St Andrews and the School of Geography and Sustainable Development is gratefully acknowledged. Continuous monitoring of glacial lakes, their parent glaciers and their surroundings is crucial because possible outbursts of these lakes pose a serious hazard to downstream areas. Ongoing climate change increases the risk of this hazard globally due to recession of glaciers leading to formation and expansion of glacial lakes, and permafrost degradation which impacts the stability of glaciers, slopes and moraines. Here, we demonstrate the capability of our approach for monitoring lake outburst susceptibility using time-series of Sentinel-1 Synthetic Aperture Radar (S-1 SAR) data. We selected Lunana in the Bhutanese Himalayas as an example region as it is highly susceptible to glacial lake outburst floods and suitable baseline data were available. We used Google Earth Engine (GEE) to calculate average radar backscatter intensity (ARBI) of glaciers, lakes, basins, and moraines. To determine the periodicity of the highest and the lowest radar backscatter intensity, we denoised the ARBI data using a Fast Fourier Transform and autocorrelated using a Pearson correlation function. Additionally, we determined glacier melt area, basin melt area, lake area, open water area, and lake ice area using radar backscatter intensity data. The Persistent Scatterer Interferometry (PSI) technique was used to investigate the stability of moraines and slopes around glacial lakes. The PSI results were qualitatively validated by comparison with high-resolution digital elevation model differencing results. Our approach showed that glaciers and basins in the region underwent seasonal and periodic changes in their radar backscatter intensity related to changes in ice and snow melt. Lakes also showed seasonal changes in their radar backscatter intensity related to the variation of lake ice and open water area, but the radar backscatter intensity change was not periodic. We could also infer lake area change using a time-series radar backscatter intensity data such as the rapid expansion of Bechung Tsho. The PSI analysis showed that all the terminal moraines were stable except Drukchung Tsho. Its terminal moraine showed subsidence at the rate of –5.18 mm/yr. Sidewalls of lakes were also stable with the exception of Lugge Tsho at site 4. Due to the free availability of S-1 SAR data, the efficiency of processing a large amount of imagery within GEE, and the PSI technique, we were able to understand the outburst susceptibility of glacial lakes in the region at great detail. The regular acquisition of S-1 SAR data enables continuous monitoring of glacial lakes. A similar approach and concept can be transferred to any geographic region on earth that shares similar challenges in glacial lake monitoring. Publisher PDF

Glaciers and rock glaciers play an important role in the hydrology of the semi-arid northern Chile. Several studies show that glaciers have rapidly lost mass in response to climate change during the last decades. The response of rock glaciers to climate change in this region is, however, less known. In this study we use a combination of historical aerial photography, stereo satellite imagery, airborne lidar, and the Shuttle Radar Topography Mission (SRTM) DEM to report glacier changes for the Tapado Glacier–rock glacier complex from the 1950s to 2020 and to report mass balances for the glacier component of the complex, Tapado Glacier. Furthermore, we examine high-resolution elevation changes and surface velocities between 2012 and 2020 for 35 rock glaciers in the La Laguna catchment. Our results show how Tapado Glacier has shrunk by -25.2±4.6 % between 1956 and 2020, while the mass balance of Tapado Glacier has become steadily more negative, from being approximately in balance between 1956 and 1978 (-0.04±0.08 m w.e. a−1) to showing increased losses between 2015 and 2020 (-0.32±0.08 m w.e. a−1). Climatological (re-)analyses reveal a general increase in air temperature, decrease in humidity, and variable precipitation since the 1980s in the region. In particular, the severe droughts starting in 2010 resulted in a negative mass balance of -0.54±0.10 m w.e. a−1 between 2012 and 2015. The rock glaciers within the La Laguna catchment show heterogenous changes, with some sections of landforms exhibiting pronounced elevation changes and surface velocities exceeding that of Tapado Glacier. This could be indicative of high ice contents within the landforms and also highlights the importance of considering how landforms can transition from more glacial landforms to more periglacial features under permafrost conditions. As such, we believe high-resolution (sub-metre) elevation changes and surface velocities are a useful first step for identifying ice-rich landforms.

Glacial lake outburst floods (GLOFs) are a major concern throughout High Mountain Asia, where impacts can be far-reaching. This is particularly true for transboundary Himalayan basins, where risks are expected to further increase as new lakes develop. Given the need for anticipatory approaches to disaster risk reduction, this study aims to demonstrate how the threat from a future lake can be feasibly assessed along-side that of current lakes, and how this information can feed practically into decision-making and response planning. We have focused on two well-known dangerous lakes (Galongco and Jialongco), comparing the consequences of simulated worst-case outburst events from these lakes both in the Tibetan town of Nyalam and downstream at the border with Nepal. In addition, a future scenario has been assessed, whereby an outburst was simulated for a potential new lake forming upstream of Nyalam. Results show that although smallest in size, Jialongco, poses the greatest immediate threat to Nyalam and downstream communities, owing to the high potential for an ice avalanche to trigger an outburst. The future lake scenario would lead to flow depths and velocities that exceed either of the current scenarios, and the peak flood would reach Nepal up to 20 minutes faster. Based on these findings, a comprehensive approach to disaster risk reduction is called for, combining early warning systems with effective land use zoning and capacity building programs. Such approaches address the current drivers of GLOF risk in the basin, while remaining robust in the face of future emerging threats.