Glacier Elevation Changes Research Articles

Rapid glacier mass loss in the Southeastern Tibetan Plateau since the year 2000 from satellite observations

Maritime glaciers in the Southeastern Tibetan Plateau (SETP) featuring the largest maritime glaciers in the Tibetan Plateau (TP) have been experiencing dramatic mass loss and interannual variability over the past two decades, increasing risks of glacier avalanches and glacial lake outbursts. However, spatially explicit and high-temporal-resolution glacier mass loss over the entire SETP has not been well quantified. We developed an approach to integrate satellite altimetry (ICESat, CryoSat-2, and ICESat-2) with DEM differencing and satellite gravity to resolve high spatiotemporally resolved glacier surface elevation change and mass balance across the SETP for the past two decades. We generated DEMs from ASTER L1A stereo-images to estimate the multi-year elevation change, which was used to correct for the altimetry-based counterpart. Subsequently, we processed three different satellite altimetry data and total water storage (TWS) products specifically. Finally, we obtained time series of glacier elevation change and mass balance through the integration of satellite altimetry-, satellite gravity-, and DEM-derived elevation changes during 2000–2020. Results show rapid and heterogeneous glacier depletion with a mean mass loss rate of −0.66 ± 0.02 m water equivalent (w.e.)/yr during 2003–2020 and an accelerating trend over the past two decades. The strongest downwasting was observed in the Hengduan Mountains (−1.29 ± 0.32 m w.e./yr). Contiguous glaciers distributed mostly in Bomi County have a slower rate of elevation changes but play a dominant role in the regional mass balance. Glacier terminus types have a significant impact on glacier melting. The mass loss rate of lake-terminating glaciers is 45% higher than that of land-terminating glaciers, suggesting increasing risks of glacial lake outbursts caused by rapid glacier melting across the SETP. These spatially explicit and high-temporal-resolution features of glacier mass loss will be extremely valuable for calibrating and validating glaciological and hydrological models. Our approach also shows a promising application of CryoSat-2 to mountain glaciology and its potential of estimating glacier mass balances over similar regions globally.

Research on glacier elevation changes in Southeast Tibet based ICESat and CryoSat-2 Data

Based on the comprehensive analysis of ICESat/GLAS14 data from 2003 to 2009 and CryoSat-2/L2I data from 2010 to 2016 in summer season. This paper revealed the elevation changes of mountain glaciers in small watershed scale in southeastern Qinghai-Tibet Plateau by using outliner elevation of footprints, spatial matching analysis of DEM and elevation trends simulation methods. The result showed, the data of effective footprints of ICESat is significantly higher than CryoSat data on mountain glaciers. Glaciers in the study area has been regressed significantly from 2003 to 2016, with the average regression rate in the study area is -1.05±0.53ma-1, and a correlation coefficient of 0.72. Compared with the result of other similar studies in southeastern Tibet, the mountain glacier regression rate is credible. Meanwhile, the feasibility of mountain glacier elevation change monitoring in small watershed by CryoSat-2 data has been proven.

Geometric Evolution of the Chongce Glacier during 1970–2020, Detected by Multi-Source Satellite Observations

Glacier surge, which causes a quick movement of ice mass from high to low elevation, is closely associated to the glacial hazards of debris flows and glacial lake outburst floods. Over the West Kunlun Shan, surge events have been detected for some glaciers, however, the characteristics (e.g., the active phase) of the identified surge-type glaciers are not fully understood due to the paucity of long-term observations of glacier changes. In this study, we investigated the geometric evolution of the Chongce Glacier (a surge-type glacier) over the past five decades. Glacier elevation changes were observed by comparing topographic data from different times. Surface velocity and terminus position were derived using a cross-correlation algorithm and band ratio method, respectively. A decreasing rate of glacier surface thinning was found for the Chongce Glacier during the studied period. Glacier elevation changes of −0.46 ± 0.12, −0.12 ± 0.05, and 0.27 ± 0.11 m yr−1 were estimated for the periods of 1970–2000, 2000–2012, and 2012–2018, respectively. Moreover, this glacier experienced obvious surface lowering over the terminus zone and clear surface thickening over the upper zone during 1970–2000, and the opposite during 2000–2018. Surface velocity of the Chongce Glacier was less than 300 m yr−1 in 1990–1993, and then quickly increased to more than 1000 m yr−1 between 1994 and 1998, and dropped to less than 50 m yr−1 in 1999–2020. Over the past five decades, the Chongce Glacier generally experienced a slight retreat, except for a terminus advance from 1995 to 1999. According to the spatial pattern of glacier elevation changes in 1970–2000 and the long-term changes of glacier velocity and terminus position, the recent surge event at the Chongce Glacier likely initiated in winter 1993 and terminated in winter 1998. Furthermore, the start date, end date, and duration of the active phase indicate that the detected surge event was likely triggered by a thermal mechanism.

SAR-derived flow velocity and its link to glacier surface elevation change and mass balance

Modern remote sensing techniques, such as Synthetic Aperture Radar (SAR), can measure the direction and intensity of glacier flow. Yet the question remains as to what these measurements reveal about glaciers' adjustment to the warming climate. Here, we present a technique that addresses this question by linking the SAR-derived velocity measurements with the glacier elevation change and the specific mass balance (i.e. mass balance per unit area). The technique computes the speckle offset tracking results from the north, east and vertical flow displacement time series, with the vertical component further split into a Surface Parallel Flow (SPF) advection component due to the motion along a glacier surface slope and a non-Surface Parallel Flow (nSPF). The latter links the glacier surface elevation change with the specific mass balance and strain rates. We apply this technique to ascending and descending Sentinel-1 data to derive the four-dimensional flow displacement time series for glaciers in southeast Alaska during 2016–2019. Time series extracted for a few characteristic regions demonstrate remarkable temporal variability in flow velocities. The seasonal signal observed in the nSPF component is modeled using the Positive Degree Day model. This method can be used for computing either mass balance or glacier surface elevation change if one of these two parameters is known from external observations.

Continuous Estimates of Glacier Mass Balance in High Mountain Asia Based on ICESat‐1,2 and GRACE/GRACE Follow‐On Data

AbstractGlacier melt in High Mountain Asia (HMA) is an indicator of climate change and has a major impact on the regional hydrology and freshwater supply. We determined the recent status of HMA glaciers based on the first analysis of Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2) data. We used the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On (FO) data to complement ICESat‐1,2 data and validate them independently. We find a good agreement between ICESat‐1,2 and GRACE/GRACE‐FO data, which demonstrates the high reliability of results. Based on our results, the continuous glacier mass change from 2003 to 2019 is −28 ± 6 Gt yr−1, which is more negative than stereo imagery‐based studies. The regional variability of the glaciers ranges from −1.07 ± 0.10 m yr−1 in southeastern Nyaingentanglha to +0.16 ± 0.10 m yr−1 in West Kunlun. ICESat‐2 data enable new insight into the continuous measurement of HMA glacier elevation change.

Novel Techniques for Void Filling in Glacier Elevation Change Data Sets

The increasing availability of digital elevation models (DEMs) facilitates the monitoring of glacier mass balances on local and regional scales. Geodetic glacier mass balances are obtained by differentiating DEMs. However, these computations are usually affected by voids in the derived elevation change data sets. Different approaches, using spatial statistics or interpolation techniques, were developed to account for these voids in glacier mass balance estimations. In this study, we apply novel void filling techniques, which are typically used for the reconstruction and retouche of images and photos, for the first time on elevation change maps. We selected 6210 km2 of glacier area in southeast Alaska, USA, covered by two void-free DEMs as the study site to test different inpainting methods. Different artificially voided setups were generated using manually defined voids and a correlation mask based on stereoscopic processing of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) acquisition. Three “novel” (Telea, Navier–Stokes and shearlet) as well as three “classical” (bilinear interpolation, local and global hypsometric methods) void filling approaches for glacier elevation data sets were implemented and evaluated. The hypsometric approaches showed, in general, the worst performance, leading to high average and local offsets. Telea and Navier–Stokes void filling showed an overall stable and reasonable quality. The best results are obtained for shearlet and bilinear void filling, if certain criteria are met. Considering also computational costs and feasibility, we recommend using the bilinear void filling method in glacier volume change analyses. Moreover, we propose and validate a formula to estimate the uncertainties caused by void filling in glacier volume change computations. The formula is transferable to other study sites, where no ground truth data on the void areas exist, and leads to higher accuracy of the error estimates on void-filled areas. In the spirit of reproducible research, we publish a software repository with the implementation of the novel void filling algorithms and the code reproducing the statistical analysis of the data, along with the data sets themselves.

Automated Processing of Declassified KH-9 Hexagon Satellite Images for Global Elevation Change Analysis Since the 1970s

Observing changes in Earth surface topography is crucial for many Earth science disciplines. Documenting these changes over several decades at regional to global scale remains a challenge due to the limited availability of suitable satellite data before the year 2000. Declassified analog satellite images from the American reconnaissance program Hexagon (KH-9), which surveyed nearly all land surfaces from 1972 to 1986 at metric resolution, provide a unique opportunity to fill the gap in observations. However, large-scale processing of analog imagery remains challenging. We developed an automated workflow to generate Digital Elevation Models (DEMs) and orthophotos from scanned KH-9 mapping camera stereo images. The workflow includes a preprocessing step to correct for film and scanning distortions and crop the scanned images, and a stereo reconstruction step using the open-source NASA Ames Stereo Pipeline. The processing of several hundreds of image pairs enabled us to estimate reliable camera parameters for each KH-9 mission, thereby correcting elevation biases of several tens of meters. The resulting DEMs were validated against various reference elevation data, including snow-covered glaciers with limited image texture. Pixel-scale elevation uncertainty was estimated as 5 m at the 68% confidence level, and less than 15 m at the 95% level. We evaluated the uncertainty of spatially averaged elevation change and volume change, both from an empirical and analytical approach, and we raise particular attention to large-scale correlated biases that may impact volume change estimates from such DEMs. Finally, we present a case study of long-term glacier elevation change in the European Alps. Our results show the suitability of these historical images to quantitatively study global surface change over the past 40-50 years.

60 Years of Glacier Elevation and Mass Changes in the Maipo River Basin, Central Andes of Chile

Glaciers in the central Andes of Chile are fundamental freshwater sources for ecosystems and communities. Overall, glaciers in this region have shown continuous recession and down-wasting, but long-term glacier mass balance studies providing precise estimates of these changes are scarce. Here, we present the first long-term (1955–2013/2015), region-specific glacier elevation and mass change estimates for the Maipo River Basin, from which the densely populated metropolitan region of Chile obtains most of its freshwater supply. We calculated glacier elevation and mass changes using historical topographic maps, Shuttle Radar Topography Mission (SRTM), TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X), and airborne Light Detection and Ranging (LiDAR) digital elevation models. The results indicated a mean regional glacier mass balance of −0.12 ± 0.06 m w.e.a−1, with a total mass loss of 2.43 ± 0.26 Gt for the Maipo River Basin between 1955–2013. The most negative glacier mass balance was the Olivares sub-basin, with a mean value of −0.29 ± 0.07 m w.e.a−1. We observed spatially heterogeneous glacier elevation and mass changes between 1955 and 2000, and more negative values between 2000 and 2013, with an acceleration in ice thinning rates starting in 2010, which coincides with the severe drought. Our results provide key information to improve glaciological and hydrological projections in a region where water resources are under pressure.

Detailed quantification of glacier elevation and mass changes in South Georgia

Most glaciers in South America and on the Antarctic Peninsula are retreating and thinning. They are considered strong contributors to global sea level rise. However, there is a lack of glacier mass balance studies in other areas of the Southern Hemisphere, such as the surrounding Antarctic Islands. Here, we present a detailed quantification of the 21st century glacier elevation and mass changes for the entire South Georgia Island using bi-static synthetic aperture radar interferometry between 2000 and 2013. The results suggest a significant mass loss since the beginning of the present century. We calculate an average glacier mass balance of −1.04 ± 0.09 m w.e.a−1 and a mass loss rate of 2.28 ± 0.19 Gt a−1 (2000–2013), contributing 0.006 ± 0.001 mm a−1 to sea-level rise. Additionally, we calculate a subaqueous mass loss of 0.77 ± 0.04 Gt a−1 (2003–2016), with an area change at the marine and lake-terminating glacier fronts of −6.58 ± 0.33 km2 a−1, corresponding to ∼4% of the total glacier area. Overall, we observe negative mass balance rates in South Georgia, with the highest thinning and retreat rates at the large outlet glaciers located at the north-east coast. Although the spaceborne remote sensing dataset analysed in this research is a key contribution to better understanding of the glacier changes in South Georgia, more detailed field measurements, glacier dynamics studies or further long-term analysis with high-resolution regional climate models are required to precisely identify the forcing factors.

Elevation Changes of West-Central Greenland Glaciers From 1985 to 2012 From Remote Sensing

Greenlandic glaciers distinct from the ice sheet make up 12% of the global glacierized area and store about 10% of the global glacier ice volume (Farinotti et al., 2019). However, knowledge about recent climate change-induced volume changes of these 19,000 individual glaciers is limited. The small number of available glaciological and geodetic mass-balance observations have a limited spatial coverage, and the representativeness of these measurements for the region is largely unknown, factors which make a regional assessment of mass balance challenging. Here we use two recently released digital elevation models (DEMs) to assess glacier-wide elevation changes of 1,526 glaciers covering 3,785 km2 in west-central Greenland: The historical AeroDEM representing the surface in 1985 and a TanDEM-X composite representing 2010–2014. The results show that on average glacier surfaces lowered by about 14.0 ± 4.6 m from 1985 until 2012 or 0.5 ± 0.2 m yr−1, which is equivalent to a sample mass loss of ~45.1 ± 14.9 Gt in total or 1.7 ± 0.6 Gt yr−1. Challenges arise from the nature of the DEMs, such as large areas of data voids, fuzzy acquisition dates, and potential radar penetration. We compared several different interpolation methods to assess the best method to fill data voids and constrain unknown survey dates and the associated uncertainties with each method. The potential radar penetration is considered negligible for this assessment in view of the overall glacier changes, the length of the observation period, and the overall uncertainties. A comparison with earlier studies indicates that for glacier change assessments based on ICESat, data selection and averaging methodology strongly influences the results from these spatially limited measurements. This study promotes improved assessments of the contribution of glaciers to sea-level rise and encourages to extend geodetic glacier mass balances to all glaciers on Greenland.

Lake water and glacier mass gains in the northwestern Tibetan Plateau observed from multi-sensor remote sensing data: Implication of an enhanced hydrological cycle

Lakes and glaciers are widely distributed in the northwestern Tibetan Plateau. A synchronized examination of lake and glacier mass variations there has not previously been conducted, which has limited the understanding of the lake water balance and the hydrologic cycle in the region. In this study, we comprehensively examine lake area and volume, and glacier mass changes using multi-sensor satellite data. We find that lake expansion in the northwestern Tibetan Plateau was more robust from 1976 to 2018 when compared to other regions of the plateau, especially for the glacier-fed and endorheic lakes. Lake volume changes show that most of the lakes had an increase in water volume, particularly in 2000–2018 with a total water storage gain of ~28.6 Gt. By using high-resolution KH-9 and TanDEM-X data, we observe that the glacier surface elevation of the western Kunlun Mountains had a slight thinning rate of −0.07 ± 0.16 m/yr in 1973–2000, but a positive rate of 0.002 ± 0.003 m/yr in 2000–2018. The heterogeneous pattern of glacier elevation changes between the north (N) and south (S) slopes are revealed, i.e. -0.02 ± 0.01 m/yr (N) against −0.12 ± 0.03 m/yr (S) in 1973–2000 and − 0.05 ± 0.02 m/yr (N) against 0.06 ± 0.02 m/yr (S) in 2000–2018. Overall, the glaciers trend to a stable state (~0.05 m/yr) in both the south slope of the western Kunlun Mountains and Aru Co regions between 2000 and 2018. Similar patterns are also found for basin-wide examinations of lake storage changes (mass gains) and glacier mass budgets (positive or close to stable). The seasonal snow cover area changes, derived from cloud-free MODIS snow cover products, present a variable and insignificant trend between 2003 and 2017. Snow depth derived from passive microwave remote-sensing data, exhibits a decreasing trend between 1979 and 2015, but the water equivalent could contribute only an insignificant amount to the observed lake changes. The lake water gains, and almost positive glacier mass balance imply that the hydrological cycle in the northwestern Tibetan Plateau has become enhanced.

The Ice, Cloud, and Land Elevation Satellite – 2 mission: A global geolocated photon product derived from the Advanced Topographic Laser Altimeter System

The Ice, Cloud, and land Elevation Satellite – 2 (ICESat-2) observatory was launched on 15 September 2018 to measure ice sheet and glacier elevation change, sea ice freeboard, and enable the determination of the heights of Earth's forests. ICESat-2's laser altimeter, the Advanced Topographic Laser Altimeter System (ATLAS) uses green (532 nm) laser light and single-photon sensitive detection to measure time of flight and subsequently surface height along each of its six beams. In this paper, we describe the major components of ATLAS, including the transmitter, the receiver and the components of the timing system. We present the major components of the ICESat-2 observatory, including the Global Positioning System, star trackers and inertial measurement unit. The ICESat-2 Level 1B data product (ATL02) provides the precise photon round-trip time of flight, among other data. The ICESat-2 Level 2A data product (ATL03) combines the photon times of flight with the observatory position and attitude to determine the geodetic location (i.e. the latitude, longitude and height) of the ground bounce point of photons detected by ATLAS. The ATL03 data product is used by higher-level (Level 3A) surface-specific data products to determine glacier and ice sheet height, sea ice freeboard, vegetation canopy height, ocean surface topography, and inland water body height.

Glacier elevation change in the Western Qilian mountains as observed by TerraSAR-X/TanDEM-X images

The glaciers in the Qilian mountains are a major water resource for the arid Hexi corridor and Qaidam basin. With the climate becoming warmer and wetter, it is essential to study the glacier elevation changes in this region. We used TerraSAR-X/TanDEM-X images, SRTM DEM data and differential synthetic aperture radar interferometry (DInSAR) technology to analyse the glacier elevation change. Results show that the glacier elevation is changing at the rate of –0.35 m yr−1 in the western Qilian mountains between 2000 and 2014. The glacier elevation thinning at –0.40 m yr−1 in the southern part of this region is more severe than that in the northern part (–0.29 m yr−1). The long-term equilibrium line altitude, calculated from glacier elevation change in each elevation bin, was at 5150 m, which is equal to that inferred from glacial area distribution in each elevation bin. Glacier shrinkage is related to air temperature increasing.

Accelerated glacier mass loss (2011–2016) over the Puruogangri ice field in the inner Tibetan Plateau revealed by bistatic InSAR measurements

The temporal variation of glacier mass balance during recent years remains poorly known for the mountain glaciers in the inner Tibetan Plateau (ITP), due to the lack of field measurements. In this study, we retrieved the annual glacier mass balance of the Puruogangri ice field, which is the largest modern ice mass in the ITP, by differencing multi-temporal digital elevation models (DEMs) generated with five pairs of TanDEM-X bistatic interferometric synthetic aperture radar (InSAR) images acquired between April 2011 and January 2016. We compared the TanDEM-X DEMs in January and April 2012 to estimate the X-band radar penetration depth difference (0.61 ± 0.06 m), which enabled systematic bias correction in the estimation of annual glacier mass balance. The observed mass balance reveals a glacier mass gain of 0.44 ± 0.10 m w.e. yr−1 in 2011–12, which was followed by accelerated glacier mass loss in 2012–16. Glacier mass balances of −0.13 ± 0.03, −0.34 ± 0.06, and − 0.52 ± 0.10 m w.e. yr−1 were estimated for the periods of 2012–13, 2013–14, and 2014–16, respectively. This accelerating trend of glacier mass loss is likely caused by the continuous decrease in annual precipitation, according to the climate data recorded by adjacent meteorological stations. This study demonstrates that repeated bistatic InSAR measurement is a promising method for monitoring glacier elevation change and mass balance at regular intervals.

ICE SHEET ELEVATION MAPPING AND CHANGE DETECTION WITH THE ICE, CLOUD AND LAND ELEVATION SATELLITE-2

Abstract. On September 15, 2018, ICESat-2 (Ice, Cloud, and land Elevation satellite) was successfully launched to measure ice sheet and glacier elevation change, sea ice freeboard, and vegetation. This paper describes the computation of surface elevation change rates obtained with SERAC (Surface Elevation Reconstruction And Change detection) from ICESat-2 observations. After summarizing some relevant aspects of ICESat-2 and its sole instrument ATLAS (Advanced Topographic Laser Altimetry System) the paper focuses on how we calculate time series of elevation change rates from ICESat-2’s data product ATL03. Since real ICESat-2 data suitable for generating time series of several time epochs are not yet available, we used simulated data for this study. We will start generating time series from real ICESat-2 data after the conclusion of the ongoing calibration and validation phase and we expect to present real-world examples at the WG III/9 meeting in June, 2019 in Enschede, The Netherlands.

INVESTIGATION OF MOUNTAIN GLACIER STORAGE AND ITS CHANGES DURING 2000–2016 IN THE WESTERN TIBETAN PLATEAU USING COMBINED GROUND AND SATELLITE OBSERVATIONS

Abstract. The Upper Indus River Basin (UIB) has developed the largest midlatitude mountain glaciers worldwide. Ice thickness and volume distribution are important prerequisites for glaciological and hydrological investigations. In this paper, we presented detailed estimates of ice thickness in UIB region. Using ground penetrating radar, we measured glacier ice thickness on six typical glaciers; we obtained the parameters of the GlabTOP2 from these measurements and analyzed its uncertainty. Using the verified GlabTOP2 model, we simulated glacier ice thickness and volume in UIB subcatchments. The simulated results indicated that the UIB glacier thickness distribution was not uniform, ranging from 0 to 488 m, with an average thickness of 78 m. Total volume was defined as 1269.70 km3 in 2000, which corresponded to 1142.73 km3 water volume. According to the calculated discharge data from the Besham hydrological station, the total glacier volume of UIB generally can supply water resources for the downstream area for at least 15 years. And the glacier surface elevations generally decreased from 2000 to 2016 in UIB subbasins, although there was significant spatial heterogeneity in the seven subcatchments. The annual glacier surface elevation change rate of the Hindu Kush area was the smallest, followed by that of the Karakoram. The greatest glacier elevation change rate was observed in the Western Himalaya, indicating rapid glacial melting.

Glacial lake evolution and glacier–lake interactions in the Poiqu River basin, central Himalaya, 1964–2017

ABSTRACTDespite previous studies, glacier–lake interactions and future lake development in the Poiqu River basin, central Himalaya, are still not well understood. We mapped glacial lakes, glaciers, their frontal positions and ice flow from optical remote sensing data, and calculated glacier surface elevation change from digital terrain models. During 1964–2017, the total glacial-lake area increased by ~110%. Glaciers retreated with an average rate of ~1.4 km2a−1between 1975 and 2015. Based on rapid area expansion (>150%), and information from previous studies, eight lakes were considered to be potentially dangerous glacial lakes. Corresponding lake-terminating glaciers showed an overall retreat of 6.0 ± 1.4 to 26.6 ± 1.1 m a−1and accompanying lake expansion. The regional mean glacier elevation change was −0.39 ± 0.13 m a−1while the glaciers associated with the eight potentially dangerous lakes lowered by −0.71 ± 0.05 m a−1from 1974 to 2017. The mean ice flow speed of these glaciers was ~10 m a−1from 2013 to 2017; about double the mean for the entire study area. Analysis of these data along with climate observations suggests that ice melting and calving processes play the dominant role in driving lake enlargement. Modelling of future lake development shows where new lakes might emerge and existing lakes could expand with projected glacial recession.

Geodetic glacier mass balance (1975–1999) in the central Pamir using the SRTM DEM and KH-9 imagery

ABSTRACTMultiple studies on regional glacier mass balance in the Pamir Mountains have been conducted using the geodetic method, but they were rarely extended to the period before 2000. In this study, we used KH-9 imagery acquired in 1975 to generate the historical DEM for the central Pamir, and then obtained the glacier elevation change by comparing this with the SRTM C-band DEM. The penetration depth of the C-band radar was corrected for different glacier surfaces, i.e. 2.96, 1.68 and 0 m for firn/snow cover, bare ice and debris-covered areas, respectively. The final results suggest that the central Pamir glaciers, overall, experienced a near-zero mass balance of −0.03 ± 0.24 m w.e. a−1 for 1975–99. Due to glacier surge activity, the elevation change patterns of individual glaciers were highly variable, and their mass balances varied from −0.12 ± 0.26 to 0.63 ± 0.20 m w.e. a−1. The mean mass budgets of the surge-type glaciers and non-surge-type glaciers were 0.03 ± 0.14 and −0.05 ± 0.28 m w.e. a−1, respectively. Concurring with previous studies, we conclude that the central Pamir glaciers may have been in a state of approximately balanced mass budget or slight mass deficit from the mid-1970s to the mid-2010s.

Performance Assessment of TanDEM-X DEM for Mountain Glacier Elevation Change Detection

TanDEM-X digital elevation model (DEM) is a global DEM released by the German Aerospace Center (DLR) at outstanding resolution of 12 m. However, the procedure for its creation involves the combination of several DEMs from acquisitions spread between 2011 and 2014, which casts doubt on its value for precise glaciological change detection studies. In this work we present TanDEM-X DEM as a high-quality product ready for use in glaciological studies. We compare it to Aerial Laser Scanning (ALS)-based dataset from April 2013 (1 m), used as the ground-truth reference, and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) V003 DEM and SRTM v3 DEM (both 30 m), serving as representations of past glacier states. We use a method of sub-pixel coregistration of DEMs by Nuth and Kääb (2011) to determine the geometric accuracy of the products. In addition, we propose a slope-aspect heatmap-based workflow to remove the errors resulting from radar shadowing over steep terrain. Elevation difference maps obtained by subtraction of DEMs are analyzed to obtain accuracy assessments and glacier mass balance reconstructions. The vertical accuracy (± standard deviation) of TanDEM-X DEM over non-glacierized area is very good at 0.02 ± 3.48 m. Nevertheless, steep areas introduce large errors and their filtering is required for reliable results. The 30 m version of TanDEM-X DEM performs worse than the finer product, but its accuracy, −0.08 ± 7.57 m, is better than that of SRTM and ASTER. The ASTER DEM contains errors, possibly resulting from imperfect DEM creation from stereopairs over uniform ice surface. Universidad Glacier has been losing mass at a rate of −0.44 ± 0.08 m of water equivalent per year between 2000 and 2013. This value is in general agreement with previously reported mass balance estimated with the glaciological method for 2012–2014.

Constraining glacier elevation and mass changes in South America

Excluding the large ice sheets of Greenland and Antarctica, glaciers in South America are large contributors to sea-level rise1. Their rates of mass loss, however, are poorly known. Here, using repeat bi-static synthetic aperture radar interferometry over the years 2000 to 2011/2015, we compute continent-wide, glacier-specific elevation and mass changes for 85% of the glacierized area of South America. Mass loss rate is calculated to be 19.43 ± 0.60 Gt a−1 from elevation changes above ground, sea or lake level, with an additional 3.06 ± 1.24 Gt a−1 from subaqueous ice mass loss not contributing to sea-level rise. The largest contributions come from the Patagonian icefields, where 83% mass loss occurs, largely from dynamic adjustments of large glaciers. These changes contribute 0.054 ± 0.002 mm a−1 to sea-level rise. In comparison with previous studies2, tropical and out-tropical glaciers — as well as those in Tierra del Fuego — show considerably less ice loss. These results provide basic information to calibrate and validate glacier-climate models and also for decision-makers in water resource management3. Synthetic aperture radar interferometry reveals that 19 Gt of ice is lost per year from glaciers in South America — mostly from Patagonia — contributing 0.04 mm annually to global sea-level rise.