Specific Mass Balance Research Articles

Two-Decadal Glacier Changes in the Astak, a Tributary Catchment of the Upper Indus River in Northern Pakistan

Snow and ice melting in the Upper Indus Basin (UIB) is crucial for regional water availability for mountainous communities. We analyzed glacier changes in the Astak catchment, UIB, from 2000 to 2020 using remote sensing techniques based on optical satellite images from Landsat and ASTER digital elevation models. We used a surface feature-tracking technique to estimate glacier velocity. To assess the impact of climate variations, we examined temperature and precipitation anomalies using ERA5 Land climate data. Over the past two decades, the Astak catchment experienced a slight decrease in glacier area (−1.8 km2) and the overall specific mass balance was −0.02 ± 0.1 m w.e. a−1. The most negative mass balance of −0.09 ± 0.06 m w.e. a−1 occurred at elevations between 2810 to 3220 m a.s.l., with a lesser rate of −0.015 ± 0.12 m w.e. a−1 above 5500 m a.s.l. This variation in glacier mass balance can be attributed to temperature and precipitation gradients, as well as debris cover. Recent glacier mass loss can be linked to seasonal temperature anomalies at higher elevations during winter and autumn. Given the reliance of mountain populations on glacier melt, seasonal temperature trends can disturb water security and the well-being of dependent communities.

How to handle glacier area change in geodetic mass balance

Abstract Innovations in geodesy enable widespread analysis of glacier surface elevation change and geodetic mass balance. However, coincident glacier area data are less widely available, causing inconsistent handling of glacier area change. Here we quantify the bias introduced into meters water equivalent (m w.e.) specific geodetic mass balance results when using a fixed, maximum glacier area, and illustrate the bias for five North American glaciers. Sites span latitudes from the northern U.S. Rocky Mountains (48°N) to the Central Alaska Range (63°N) between 1948 and 2021. Results show that fixed (maximum) area treatment subdues the m w.e. mass change signal, underestimating mass balance by up to 19% in our test cases. This bias scales with relative glacier area change and the mass balance magnitude. Thus, the bias for specific geodetic mass balances will be most pronounced across rapidly deglaciating regions. Our analysis underscores the need for temporally resolved glacier area in geodetic mass balance studies.

Magnesium and groundwater flow relationship in karst aquifers: a tool for exploitation management of springs

Karst aquifers are characterized by different types of groundwater flow, related to different types of permeability due to the simultaneous presence of matrix, fractures and conduits. The presence of a well-developed karst conduit system leads to a rapid circulation of groundwater within the aquifer and a pulse-type response of the spring flow to the rainfall inputs, with a potential fast transport of contaminants from the hydrogeological basin surface to the discharge zones. Supported by hydro chemical analyses of spring water samples and single discharge measurements, it was possible to develop specific mass balance models, correlating ion content to spring flowrates. Specifically, Mg2+ content revealed a reliable application for spring baseflow separation in karst settings. Once the local model has been set, its conservative behaviour, in mostly limestone-dominant aquifers, allows using Mg2+ as a natural tracer of groundwater flow, distinguishing conduit flow (overflow) and diffuse flow (baseflow) occurrence in the spring outlet, without additional discharge measurements. In karst settings, the difficulty in continuously monitoring the spring discharge values makes this application interesting for exploitation management. This study shows the results obtained for two springs located in Central Italy, confirming that monitoring groundwater quality in karst environments is often the key for successfully characterizing springs and assessing the total yield when direct measurements are not available.

Influence of climate and non-climatic attributes on declining glacier mass budget and surging in Alaknanda Basin and its surroundings

Globally glaciers are rapidly shrinking, endangering the sustainability of melt water and altering the regional hydrology. Understanding long-term glacier response to climate change and the influence of non-climatic attributes like morpho-topographic factors on ice loss is of high relevance. Here we estimate the multi-temporal mass balance of 445 glaciers in the upper Alaknanda basin and neighboring transboundary glaciers using optical stereo imageries from 1973 to 2021. Our measurements indicate a mean annual area change rate of −1.14 ± 0.07 km2 a−1 and a geodetic glacier mass balance of −0.34 ± 0.08 m w.e. a−1 from 1973 to 2020, leading to an overall mass loss of 12.9 ± 1.7 Gt, that accounts for up to 0.036 ± 0.006 mm of sea level rise. Before 2000 (1973–2000), the mean regional glacier mass loss rate was −0.30 ± 0.07 m w.e. a−1, which increased to −0.43 ± 0.06 m w.e. a−1 during 2000–2020. ERA5 Land reanalysis data showed a summer and annual temperature rise of ∼0.6 °C and ∼ 0.5 °C respectively in recent time period (2015–2020) and consequent strong mass loss (−0.68 ± 0.09 m w.e. a−1). In addition to climatic influence, glacier morphometry, topographic features and uneven debris cover distribution further impacted the regional and glacier specific mass balance. Our multi-temporal observation from space also emphasized that though the glaciers in this region experienced an increasing mass loss but a strong heterogeneous glacier specific response, like surging and dynamic separation of glacier, are also evident that was not captured by the available long-term global elevation change grids. Among all the climatic and non-climatic attributes, we identified summer temperature having most significant influence over glacier mass budget in this region, with a mass balance sensitivity of −0.6 m w. e. a−1 °C−1. Hence, knowing the mean summer temperature will help to predict the mass balance for any intermediate year for this region. If such climatic trend continues, smaller glaciers are likely to disapear in coming decades. Similar studies in other parts of the world and on specific glaciers can reveal links with climate factors, reconstruct mass balance, and enhance comprehension of glacier response to climate change. Our geodetic mass balance estimates will improve the estimation of meltwater run-off component of the hydrological cycle in this part of the Himalaya, which could be used to calibrate/validate glacier mass balance models.

Mass balance of Nehnar glacier from 2000 to 2020, using temperature indexed-IAAR approach.

Glacier mass balance is inextricably linked to annual meteorological conditions and is a key indicator for assessing the ice reserves of a glacier. As a result, a number of studies have estimated glacier mass balance using different methods. Here, we have used the improved accumulation area-ratio (IAAR) method to study the mass balance of the Nehnar glacier from 2000 to 2020. This study also aims to study the spatiotemporal behavior and other dynamics of the glacier. Results have shown that the glacier has continuously lost its ice reserves throughout the studied period though at a lower rate since 2010. Its annual specific mass balance has changed from - 50.10 ± 3 cm w.e in 2000 to - 59.46 ± 3 cm w.e. in 2020. The equilibrium line altitude (ELA) of the glacier rose by 90 m and has shifted from 4260 masl in 2000 to 4350 masl in 2020. The glacier has shrunk from an area of 1.64 km2 in 2000 to 1.38 km2 in 2020 losing nearly 16% of its area. The study highlights the need for continued monitoring of glacier mass balance to better understand and predict the effects of climate change. These findings have important implications for the future of glacier retreat and water reserves of the Jhelum basin.

Future state of Norwegian glaciers: Estimating glacier mass balance and equilibrium line responses to projected 21st century climate change

Glaciers and ice caps in Norway are presently undergoing mass loss, areal reduction, and frontal retreat, mainly a result of increased summer ablation due to rising summer temperatures over Scandinavia, especially after 2000 CE. In this paper, the glacier mass-balance response of 10 Norwegian glaciers with continuous mass balance observations (>10 years) to climate projections from 1971–2000 to 2071–2100 have been estimated. Projected changes in mean summer temperature and mean winter precipitation from 1971–2000 to 2071–2100, applying the RCP8.5 emission scenario for five different regions in Norway; ‘Sogn og Fjordane’ and ‘Hordaland’, now Vestland County in western Norway, ‘Oppland’, now part of Innlandet County in eastern Norway, and Nordland County and Finnmark County, both in Northern Norway), range between +3.5°C and +5.0°C, and between +5% and +25%, respectively. These climate projections have been converted (by linear regression with overlapping observational mass-balance data) into specific surface glacier mass balance [winter balance ( Bw), summer balance ( Bs), and annual balance ( Ba) for 10 glaciers in Norway with mass-balance series [Ålfotbreen, Nigardsbreen (part of Jostedalsbreen), Austdalsbreen (part of Jostedalsbreen), Rembesdalskåka (part of Hardangerjøkulen), Blomstølskardsbreen (part of Søre Folgefonna), Storbrean, Hellstugubrean, Gråsubrean, Engabreen (part of Vestre Svartisen, Langfjordjøkelen (data: http://glacier.nve.no/glacier/viewer/ci/no/ ) yielding a total, cumulative surface glacier mass loss from 2000 to 2100 CE in the range of -85.2 ± 4 to -197.3 ± 10 m water equivalents. The estimated changes in equilibrium-line altitudes (ELAs), in the range of 230 ± 10 to 630 ± 30 m, indicate that the mean ELA may reach the upper part of 7 of the 10 glaciers included in this study [Ålfotbreen, Austdalsbreen, Rembesdalskåka, Blomstølskardsbreen, Gråsubrean, Engabreen and Langfjordjøkelen] by the end of the 21st century. The projected glacier mass loss and ELA rise, and thus changes in glacier length, area and volume, will most likely have profound consequences for future glacier hydrology (runoff), hydropower production, wildlife, ecosystems, glacier hazards, and tourism.

Glacier Area, Mass and Associated Glacial Lake Change in Kawari basin, Western Nepal

Due to ongoing global climate change, the glaciers in the Himalaya are shrinking and the glacial lakes are increasing in number and area. This study investigates the glacier area change, mass balance and associated glacial lake evolution in the headwaters of Kawari basin, western Nepal using optical remote sensing images. The results indicate that eleven glaciers in the study area have shrunk by 1.64 km2 between 1994 and 2021. In the same period, due to glacier recession glacial lake formed and expanded by 0.0103 km2 yr-1 reaching 0.34±0.042 km2 in 2021. Surface elevation change of glaciers revealed that the ablation zone of glacier thinned up to -8.18 m between 2000 and 2019. The specific mass balance of eleven glaciers was calculated to be -0.3 m w. e. yr-1 from 2000 to 2019. The study of glaciers is important as they are visible signals of climate change, and their changes often impact water resources and mountain hydrology.

Rapid demise and committed loss of Bowman Glacier, northern Ellesmere Island, Arctic Canada

AbstractUsing historical and recent aerial photography and structure from motion (SfM) multiview stereo (MVS) techniques, we reconstruct the 1959 and 2018 ice surface topography and determine the geodetic mass balance of Bowman Glacier, a small mountain glacier on northern Ellesmere Island. This is combined with optical satellite imagery to reconstruct the evolution in extent of the glacier over six decades, and ground-penetrating radar measurements of ice thickness to estimate the remaining ice volume. Between 1959 and 2020, Bowman Glacier lost 78% of its extent (reducing from 2.75 to 0.61 km2), while average annual area loss rates have nearly tripled in the past two decades. Over the 1959–2018 period, glacier-wide ice-thickness change averaged −22.7 ± 4.7 m, corresponding to a mean specific annual mass balance of −347.0 ± 71.4 mm w.e. a−1. Projecting rates of area and volume change into the future indicates that the glacier will likely entirely disappear between 2030 and 2060. This study demonstrates the potential of SfM-MVS processing to generate elevation products from 1950/60s historical aerial photographs, and to extend observations of ice elevation and glacier volume change for the Canadian Arctic, prior to the satellite record.

The West Kunlun Glacier Anomaly and Its Response to Climate Forcing during 2002–2020

Research into glacial mass change in West Kunlun (WK) has been sufficient, but most of the existing studies were based on geodetic methods, which are not suitable for specific health state analyses of each glacier. In this paper, we utilize Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery, applying the continuity equation to obtain altitudinal specific mass balance (SMB) for 615 glaciers (>2 km2) during 2002–2011, 2011–2020, and 2002–2020 to research glacial health and its response to climatic forcing. The results show dissimilar glacier SMB patterns between 2002–2011 (0.10 ± 0.14 m w.e. a−1), 2011–2020 (–0.12 ± 0.14 m w.e. a−1) and 2002–2020 (−0.01 ± 0.07 m w.e. a−1). Additionally, the glacier equilibrium line altitude (ELA) in WK was 5788 m, 5744 m, and 5786 m, respectively, and the corresponding accumulation area ratios (AARs) were 0.59, 0.62, and 0.58, during 2002–2011, 2011–2020, and 2002–2020, respectively. Regarding glacier response, compared with the ordinary-least-square (OLS) model, the artificial neural network (ANN) model revealed a respectively less and more sensitive glacier SMB response to extreme negative and positive summer skin temperatures. In addition, the ANN model indicated that the glacier ELA was less sensitive when the integrated water vapor transport (IVT) change exceeded 0.7 kg m−1s−1. Moreover, compared with IVT (−121.57 m/kg m−1s−1), glacier ELA shifts were chiefly dominated by summer skin temperature (+154.66 m/℃) in the last two decades. From 2002–2011 and 2011–2020, glacier SMB was more susceptible to summer skin temperature (−0.38 m w.e./℃ and −0.16 m w.e./℃, respectively), while during 2002–2020, it was more influenced by IVT (0.45 m w.e./kg m−1s−1). In contrast with eastern WK, glaciers in western WK were healthier, although mitigation measures are still needed to safeguard glacier health and prevent possible natural hazards in this region. Finally, we believe that the inconsistent change between glacier SMB and ELAs from 2002–2020 was connected with ice rheology and that the combined effects of skin temperature and IVT can explain the WK glacier anomaly.

Glacier mass balance estimation in Garhwal Himalaya using improved accumulation area ratio method.

Water requirements of the mountain communities living in the Himalaya are supported by snow and glacier melt. The availability of water from the source depends on numerous climatic and glacier parameters. One key parameter is mass balance, which helps to assess the glacier health and future water availability. We have used the improved accumulation area ratio (IAAR) method to estimate mass balance in Alaknanda and Bhagirathi basins, constituting 1055 glaciers covering ~1609 km2. The mean Equilibrium Line Altitude (ELA) of the Alaknanda and Bhagirathi basins are estimated as 6147 ± 130 and 5985 ± 130m.a.s.l, respectively. The mass balance is estimated using the accumulation area ratio (AAR)-mass balance relationship. The mean specific mass balance of the Alaknanda and Bhagirathi for 2001-2013 is estimated as -1.1 ± 0.03m.w.e.a-1 and -1.01 ± 0.07m.w.e.a-1, respectively. Total mass loss from the study area is calculated as ~21.4 ± 1.1Gt during this period. The loss of glaciers in the mountain area will increase the vulnerability of communities living in the region. It suggests a need for better adaptation strategies to improve the resilience of high mountain communities.

Assessing the Contribution of Glacier Melt to Discharge in the Tropics: The Case of Study of the Antisana Glacier 12 in Ecuador

Tropical glaciers are excellent indicators of climate variability due to their fast response to temperature and precipitation variations. At same time, they supply freshwater to downstream populations. In this study, a hydro-glaciological model was adapted to analyze the influence of meteorological forcing on melting and discharge variations at Glacier 12 of Antisana volcano (4,735–5,720 m above sea level (a.s.l.), 1.68 km2, 0°29′S; 78°9′W). Energy fluxes and melting were calculated using a distributed surface energy balance model using 20 altitude bands from glacier snout to the summit at 30-min resolution for 684 days between 2011 and 2013. The discharge was computed using linear reservoirs for snow, firn, ice, and moraine zones. Meteorological variables were recorded at 4,750 m.a.s.l. in the ablation area and distributed through the altitudinal range using geometrical corrections, and measured lapse rate. The annual specific mass balance (−0.61 m of water equivalent -m w.e. y−1-) and the ablation gradient (22.76 kg m−2 m−1) agree with the values estimated from direct measurements. Sequential validations allowed the simulated discharge to reproduce hourly and daily discharge variability at the outlet of the catchment. The latter confirmed discharge simulated (0.187 m3 s−1) overestimates the streamflow measured. Hence it did not reflect the net meltwater production due to possible losses through the complex geology of the site. The lack of seasonality in cloud cover and incident short-wave radiation force the reflected short-wave radiation via albedo to drive melting energy from January to June and October to December. Whereas the wind speed was the most influencing variable during the July-September season. Results provide new insights on the behaviour of glaciers in the inner tropics since cloudiness and precipitation occur throughout the year yielding a constant short-wave attenuation and continuous variation of snow layer thickness.

A stochastic approach to evaluating the economic impact of disruptions in feedstock pipelines on downstream production

Reliability of feedstock supply is an important consideration for enhancing the safety and continuous operation of chemical plants. A critical component of the chemical and refining sectors is the extensive pipeline network which transports natural gas and hydrocarbon liquids from producing areas to refineries and chemical plants. Incidents involving spills or releases and shutdowns of those pipeline can occur due to a number of causes including corrosion, equipment malfunction, and excavation damage. These incidents involve economic, environmental, and safety consequences such as the cost of asset damage, lost commodities, cleanup requirement, and operational disruption. In this work, an appropriately developed stochastic framework is presented to determine the disruption impact of pipeline incidents on downstream chemical production. Incident data are statistically analyzed to determine meaningful distributions for incident rates, spill/release quantities, and pipeline shutdown durations. A case study on the production of propylene via three different pathways (crude oil, propane, and natural gas) is presented to illustrate the methodology and underline the variability of the process production impact due to variations in risk occurrence characteristics. Using specific process chemistry and mass balances, more precise risk profiles for the product shortfall and cost of lost sales can be generated.

Net Drawdown of Greenhouse Gases (CO2, CH4 and N2O) by a Temperate Australian Seagrass Meadow

Seagrasses have some of the highest rates of carbon burial on the planet and have therefore been highlighted as ecosystems for nature-based climate change mitigation. However, information is still needed on the net radiative forcing benefit of seagrasses inclusive of their associated greenhouse gas (GHG) emissions. Here, we report simultaneous estimates of seagrass-associated carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) air–water emissions. Applying in situ sampling within a south-east Australian seagrass ecosystem, this study finds atmospheric GHG emissions from waters above seagrasses to range from − 480 ± 15.96 to − 16.2 ± 8.32 mg CO2-equivalents m2 d−1 (net uptake), with large temporal and spatial variability. Using a combination of gas specific mass balance equations, dissolved stable carbon isotope values (δ13C) and in situ time-series data, CO2-e flux is estimated at − 21.74 mg m2 d−1. We find that the net release of CH4 (0.44 µmol m2 h−1) and net uptake of N2O (− 0.06 µmol m2 h−1) effectively negated each other at 16.12 and − 16.13 mg CO2-e m2 d−1, respectively. The results of this study indicate that temperate Australian seagrasses may function as net sinks of atmospheric CO2-e. These results contribute towards filling key emission accounting gaps both in the Australian region, and through the simultaneous measurement of the three key greenhouse gas species.

Reconstruction of the Historical (1750–2020) Mass Balance of Bordu, Kara-Batkak and Sary-Tor Glaciers in the Inner Tien Shan, Kyrgyzstan

The mean specific mass balance of a glacier represents the direct link between a glacier and the local climate. Hence, it is intensively monitored throughout the world. In the Kyrgyz Tien Shan, glaciers are of crucial importance with regard to water supply for the surrounding areas. It is therefore essential to know how these glaciers behave due to climate change and how they will evolve in the future. In the Soviet era, multiple glaciological monitoring programs were initiated but these were abandoned in the nineties. Recently, they have been re-established on several glaciers. In this study, a reconstruction of the mean specific mass balance of Bordu, Kara-Batkak and Sary-Tor glaciers is obtained using a surface energy mass balance model. The model is driven by temperature and precipitation data acquired by combining multiple datasets from meteorological stations in the vicinity of the glaciers and tree rings in the Kyrgyz Tien Shan between 1750 and 2020. Multi-annual mass balance measurements integrated over elevation bands of 100 m between 2013 and 2020 are used for calibration. A comparison with WGMS data for the second half of the 20th century is performed for Kara-Batkak glacier. The cumulative mass balances are also compared with geodetic mass balances reconstructed for different time periods. Generally, we find a close agreement, indicating a high confidence in the created mass balance series. The last 20 years show a negative mean specific mass balance except for 2008–2009 when a slightly positive mass balance was found. This indicates that the glaciers are currently in imbalance with the present climatic conditions in the area. For the reconstruction back to 1750, this study specifically highlights that it is essential to adapt the glacier geometry since the end of the Little Ice Age in order to not over- or underestimate the mean specific mass balance. The datasets created can be used to get a better insight into how climate change affects glaciers in the Inner Tien Shan and to model the future evolution of these glaciers as well as other glaciers in the region.

Geodetic Mass Balance of the South Shetland Islands Ice Caps, Antarctica, from Differencing TanDEM-X DEMs

Although the glaciers in the Antarctic periphery currently modestly contribute to sea level rise, their contribution is projected to increase substantially until the end of the 21st century. The South Shetland Islands (SSI), located to the north of the Antarctic Peninsula, are lacking a geodetic mass balance calculation for the entire archipelago. We estimated its geodetic mass balance over a 3–4-year period within 2013–2017. 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 data limitations). Our results show a close to balance, slightly negative average specific mass balance for the whole area of −0.106 ± 0.007 m w.e. a−1, representing a mass change of −238 ± 12 Mt a−1. These results are consistent with a wider scale geodetic mass balance estimation and with glaciological mass balance measurements at SSI locations for the same study period. They are also consistent with the cooling trend observed in the region between 1998 and the mid-2010s.

Twentieth century global glacier mass change: an ensemble-based model reconstruction

Abstract. Negative glacier mass balances in most of Earth's glacierized regions contribute roughly one-quarter to currently observed rates of sea-level rise and have likely contributed an even larger fraction during the 20th century. The distant past and future of glaciers' mass balances, and hence their contribution to sea-level rise, can only be estimated using numerical models. Since, independent of complexity, models always rely on some form of parameterizations and a choice of boundary conditions, a need for optimization arises. In this work, a model for computing monthly mass balances of glaciers on the global scale was forced with nine different data sets of near-surface air temperature and precipitation anomalies, as well as with their mean and median, leading to a total of 11 different forcing data sets. The goal is to better constrain the glaciers' 20th century sea-level budget contribution and its uncertainty. Therefore, five global parameters of the model's mass balance equations were varied systematically, within physically plausible ranges, for each forcing data set. We then identified optimal parameter combinations by cross-validating the model results against in situ annual specific mass balance observations, using three criteria: model bias, temporal correlation, and the ratio between the observed and modeled temporal standard deviation of specific mass balances. These criteria were chosen in order not to trade lower error estimates by means of the root mean squared error (RMSE) for an unrealistic interannual variability. We find that the disagreement between the different optimized model setups (i.e., ensemble members) is often larger than the uncertainties obtained via the leave-one-glacier-out cross-validation, particularly in times and places where few or no validation data are available, such as the first half of the 20th century. We show that the reason for this is that in regions where mass balance observations are abundant, the meteorological data are also better constrained, such that the cross-validation procedure only partly captures the uncertainty of the glacier model. For this reason, ensemble spread is introduced as an additional estimate of reconstruction uncertainty, increasing the total uncertainty compared to the model uncertainty merely obtained by the cross-validation. Our ensemble mean estimate indicates a sea-level contribution by global glaciers (outside of the ice sheets; including the Greenland periphery but excluding the Antarctic periphery) for 1901–2018 of 69.2 ± 24.3 mm sea-level equivalent (SLE), or 0.59 ± 0.21 mm SLE yr−1. While our estimates lie within the uncertainty range of most of the previously published global estimates, they agree less with those derived from GRACE data, which only cover the years 2002–2018.

Surface mass balance analysis at Naradu Glacier, Western Himalaya, India

In the present study, we analyze a field-based seven-year data series of surface mass-balance measurements collected during 2011/12 to 2017/18 on Naradu Glacier, western Himalaya, India. The average annual specific mass balance for the said period is − 0.85 m w.e. with the maximum ablation of − 1.15 m w.e. The analysis shows that the topographic features, south and southeast aspects and slopes between 7 to 24 degrees are the reasons behind the maximum ablation from a particular zone. The causes of surface mass balance variability have been analyzed through multiple linear regression analyses (MLRA) by taking temperature and precipitation as predictors. The MLRA demonstrates that 71% of the observed surface mass balance variance can be explained by temperature and precipitation. It clearly illustrates the importance of summer temperature, which alone explains 64% variance of surface mass balance. The seasonal analysis shows that most of the surface mass balance variability is described by summer temperature and winter precipitation as two predictor variables. Among monthly combinations, surface mass balance variance is best characterized by June temperature and September precipitation.

Health and sustainability of glaciers in High Mountain Asia

Glaciers in High Mountain Asia generate meltwater that supports the water needs of 250 million people, but current knowledge of annual accumulation and ablation is limited to sparse field measurements biased in location and glacier size. Here, we present altitudinally-resolved specific mass balances (surface, internal, and basal combined) for 5527 glaciers in High Mountain Asia for 2000–2016, derived by correcting observed glacier thinning patterns for mass redistribution due to ice flow. We find that 41% of glaciers accumulated mass over less than 20% of their area, and only 60% ± 10% of regional annual ablation was compensated by accumulation. Even without 21st century warming, 21% ± 1% of ice volume will be lost by 2100 due to current climatic-geometric imbalance, representing a reduction in glacier ablation into rivers of 28% ± 1%. The ablation of glaciers in the Himalayas and Tien Shan was mostly unsustainable and ice volume in these regions will reduce by at least 30% by 2100. The most important and vulnerable glacier-fed river basins (Amu Darya, Indus, Syr Darya, Tarim Interior) were supplied with >50% sustainable glacier ablation but will see long-term reductions in ice mass and glacier meltwater supply regardless of the Karakoram Anomaly.

Parametrization of a lake water dynamics model MLake in the ISBA-CTRIP land surface system (SURFEX v8.1)

Abstract. Lakes are of fundamental importance in the Earth system as they support essential environmental and economic services, such as freshwater supply. Streamflow variability and temporal evolution are impacted by the presence of lakes in the river network; therefore, any change in the lake state can induce a modification of the regional hydrological regime. Despite the importance of the impact of lakes on hydrological fluxes and the water balance, a representation of the mass budget is generally not included in climate models and global-scale hydrological modeling platforms. The goal of this study is to introduce a new lake mass module, MLake (Mass-Lake model), into the river-routing model CTRIP to resolve the specific mass balance of open-water bodies. Based on the inherent CTRIP parameters, the development of the non-calibrated MLake model was introduced to examine the influence of such hydrological buffer areas on global-scale river-routing performance. In the current study, an offline evaluation was performed for four river networks using a set of state-of-the-art quality atmospheric forcings and a combination of in situ and satellite measurements for river discharge and lake level observations. The results reveal a general improvement in CTRIP-simulated discharge and its variability, while also generating realistic lake level variations. MLake produces more realistic streamflows both in terms of daily and seasonal correlation. Excluding the specific case of Lake Victoria having low performances, the mean skill score of Kling–Gupta efficiency (KGE) is 0.41 while the normalized information contribution (NIC) shows a mean improvement of 0.56 (ranging from 0.15 to 0.94). Streamflow results are spatially scale-dependent, with better scores associated with larger lakes and increased sensitivity to the width of the lake outlet. Regarding lake level variations, results indicate a good agreement between observations and simulations with a mean correlation of 0.56 (ranging from 0.07 to 0.92) which is linked to the capability of the model to retrieve seasonal variations. Discrepancies in the results are mainly explained by the anthropization of the selected lakes, which introduces high-frequency variations in both streamflows and lake levels that degraded the scores. Anthropization effects are prevalent in most of the lakes studied, but they are predominant for Lake Victoria and are the main cause for relatively low statistical scores for the Nile River However, results on the Angara and the Neva rivers also depend on the inherent gap of ISBA-CTRIP process representation, which relies on further development such as the partitioned energy budget between the snow and the canopy over a boreal zone. The study is a first step towards a global coupled land system that will help to qualitatively assess the evolution of future global water resources, leading to improvements in flood risk and drought forecasting.

Long-term (~40 years) mass balance appraisal and response of the Patsio glacier, in the Great Himalayan region towards climate change

Comprehensive assessment of the long-term mass balance (40 years) has been performed for Patsio glacier located in Bhaga river basin in the Great Himalayan region. The temperature-index approach has been employed for generating the time-series of annual specific mass balance of 25 years (1993–2018) using Snow and Avalanche Study Establishment (SASE) field observatory data in Patsio region. Results based on observational data showed nearly balanced condition until the year 1999 (+0.03 m.w.e/yr), followed by an accelerated rate of mass loss during the period 2000–2007 (−0.17 m.w.e./yr). This was evident due to the annual rise (+0.7°C) in the temperature and drop (−122 mm) in the amount of precipitation during 2000–2007. A slight drop in the mass balance (−0.14 m.w.e/yr) was observed during the past decade (2008–2018) which was well supported by in-situ climate observations and published geodetic results in the region. The altitudinal distribution of modelled mass balance was observed well in correlation with the glaciological measurements for the periods 2010–2011 and 2011–2012. Further, seasonal sensitivity characteristic (SSC) was developed for the glacier illustrating the dependence of specific mass balance on monthly anomalies in temperature and precipitation. The developed SSC was used with bias-corrected temperature and precipitation estimates from recently released ERA5 reanalysis to reconstruct annual specific mass balance during since 1979s.