Glacier Mass Balance Changes Research Articles

Accelerated glacier mass loss in the mid-latitude Eurasia from 2019 to 2022 revealed by ICESat-2

The dynamics of glaciers serve as one of the most important indicators of climate change. Whilst current research has primarily concentrated on long-term interannual glacier mass balance and its response to climate change, glaciers may respond more rapidly to climate change, highlighting the urgent need for intra-annual mass balance estimations. Investigating seasonal or short-term variations in glacier mass balance not only enhances our understanding of the interactions between glaciers and the climate system but also provides crucial data for water resource management and ecological protection. The ICESat-2 and NASADEM datasets were used to estimate the inter- and intra-annual glacier mass balance changes in the mid-latitude Eurasia from 2019 to 2022. Additionally, the response of glacier mass balance to regional air temperature and precipitation values was analysed using ERA5-Land data and multiple regression analysis, respectively. From 2019 to 2022, glacier mass loss in mid-latitude Eurasia reached −45.02 ± 34.21 Gt per year, contributing to a global sea-level rise of 0.12 ± 0.09 mm per year. The glacier melt rate in the study area from 2019 to 2022 was 2.33 times higher than that from 2000 to 2019. With the exception of the Western Kunlun region, which experienced a weak accumulation rate of 0.04 ± 0.35 m w.e. per year, all other areas experienced ablation states. Seasonal mass balance responds differently to temperature and precipitation variations across seasons: higher temperatures in different seasons lead to more negative mass balances, while increased winter and spring precipitation can slow down glacier melt. Air temperature dominates the glacier mass balance changes in the study area. The intense heat in 2022 raised average glacier temperatures by 1.04 °C compared to 2019–2021, resulting in a more negative mass balance and an increased ice loss of −0.34 ± 1.01 m w.e. per year (−35.07 ± 103.22 Gt per year). This analysis indicates that glacier mass balance is highly sensitive to climate change, even on a seasonal scale. Moreover, the high precision and spatiotemporal resolution ICESat-2 data can facilitate the investigation of large-scale glacier mass balance on short time scales.

Remote Sensing and Modeling of the Cryosphere in High Mountain Asia: A Multidisciplinary Review

Over the past decades, the cryosphere has changed significantly in High Mountain Asia (HMA), leading to multiple natural hazards such as rock–ice avalanches, glacier collapse, debris flows, landslides, and glacial lake outburst floods (GLOFs). Monitoring cryosphere change and evaluating its hydrological effects are essential for studying climate change, the hydrological cycle, water resource management, and natural disaster mitigation and prevention. However, knowledge gaps, data uncertainties, and other substantial challenges limit comprehensive research in climate–cryosphere–hydrology–hazard systems. To address this, we provide an up-to-date, comprehensive, multidisciplinary review of remote sensing techniques in cryosphere studies, demonstrating primary methodologies for delineating glaciers and measuring geodetic glacier mass balance change, glacier thickness, glacier motion or ice velocity, snow extent and water equivalent, frozen ground or frozen soil, lake ice, and glacier-related hazards. The principal results and data achievements are summarized, including URL links for available products and related data platforms. We then describe the main challenges for cryosphere monitoring using satellite-based datasets. Among these challenges, the most significant limitations in accurate data inversion from remotely sensed data are attributed to the high uncertainties and inconsistent estimations due to rough terrain, the various techniques employed, data variability across the same regions (e.g., glacier mass balance change, snow depth retrieval, and the active layer thickness of frozen ground), and poor-quality optical images due to cloudy weather. The paucity of ground observations and validations with few long-term, continuous datasets also limits the utilization of satellite-based cryosphere studies and large-scale hydrological models. Lastly, we address potential breakthroughs in future studies, i.e., (1) outlining debris-covered glacier margins explicitly involving glacier areas in rough mountain shadows, (2) developing highly accurate snow depth retrieval methods by establishing a microwave emission model of snowpack in mountainous regions, (3) advancing techniques for subsurface complex freeze–thaw process observations from space, (4) filling knowledge gaps on scattering mechanisms varying with surface features (e.g., lake ice thickness and varying snow features on lake ice), and (5) improving and cross-verifying the data retrieval accuracy by combining different remote sensing techniques and physical models using machine learning methods and assimilation of multiple high-temporal-resolution datasets from multiple platforms. This comprehensive, multidisciplinary review highlights cryospheric studies incorporating spaceborne observations and hydrological models from diversified techniques/methodologies (e.g., multi-spectral optical data with thermal bands, SAR, InSAR, passive microwave, and altimetry), providing a valuable reference for what scientists have achieved in cryosphere change research and its hydrological effects on the Third Pole.

Attributing the streamflow variation by incorporating glacier mass balance and frozen ground into the Budyko framework in alpine rivers

The remarkable climate change has profound impact on the alpine hydrology, it remains unclear to date on the role of the changes in glacier mass balance and frozen ground degradation to the regional streamflow variation. Here, we incorporated the glacier mass balance and frozen ground degradation into the Budyko framework and used the elasticity method to attribute the variation of annual streamflow for 22 rivers in Qilian Mountains (QLM) from 1982 to 2015. The results indicate the simulated annual streamflow that considering glacier mass balance and frozen ground can explain more than 90 % of observed streamflow at a significance of p < 0.01, especially for the rivers with high glacier coverage. The elasticity method revealed the simulated streamflow variation can explain more than 91 % of variation in respect to the detected streamflow variation. It indicates the robustness of the elasticity method and highlights the ability of capturing the variation in streamflow with the Budyko framework that incorporated glacier mass balance and frozen ground. The streamflow variations in the 22 rivers of QLM were clustered into 3 classes. The distribution of the contributions of precipitation to streamflow variation in the 3 classes was consistent to the streamflow variation. The precipitation played a dominant role in the rivers with increased streamflow, and ET0 played a dominant role in the rivers with decreased streamflow in QLM. The impact of vegetation on streamflow variation illustrated the strong regional divergence with the contribution varied between −34.55 % and 36.79 %. The contribution of glacier mass balance and frozen ground degradation to streamflow variation were moderate with negative contributions of frozen ground degradation to the streamflow variation varying between −31.09 % and −0.43 %, while the contribution of glacier mass balance to variation in streamflow varied between −2.42 % and 11.63 % in QLM. The results could be help to understand the alpine hydrological processes under the background of climate warming and utilized for sustainable water resource management in inland region.

Different patterns of changes in glacier mass balance and glacier runoff over the Tarim Basin, Central Asia

AbstractThe climate change impacted glacio‐hydrological regime and thus the availability of water resources in arid region of Central Asia. The effects of climate change in the magnitude or seasonality of regional glacier runoff were still poorly understood in Central Asia. In this study, the glacier runoff, components of glacier runoff, equilibrium line altitude (ELA) and Glacier Mass Balance (GMB) during 1959–2017 are evaluated by elevation‐dependent Degree‐Day glacier melt model in eight sub‐basins of Tarim Basin over Central Asia. The impacts of climate change on glacier and hydrology are assessed. The results suggested that climatic regime shifted to more warm‐wet pattern on glacier zone after 1990 in study area. The ablation and accumulation of glaciers showed different patterns in eight sub‐basins. All sub‐basins showed a glacier mass deficit and GMB displayed a marked decreasing trend, but also exhibiting discrepancy. The mean ELA and rising rate of ELA were higher in the southern region. The glacier runoff increased significantly after 1990 in Tarim Basin, with obviously temporal and spatial variations in sub‐basins. The mean annual volume of glacier runoff was 175.8 × 108 m3. The ice melt was a larger component of glacial runoff in Tarim Basin. The influence of rainfall runoff on glacier runoff was more obviously than snow melt runoff as more precipitation fell as rain in northern region. The larger proportions of snow melt runoff imply more precipitation fell as snowfall in southern region. The elevation‐dependent contributions in glacier runoff showed differences in individual basins. Temperature and precipitation played different role for the glacier runoff increases among the sub‐basins. Differences in sensitivity of GMB and glacier runoff were distinct and vary considerably. A thorough assessment of the spatially and temporally varying melt water originated by glaciers is crucial for the success of water scarcity adaptation under climate change.

Simulating glacier mass balance and its contribution to runoff in Northern Sweden

Glaciers are one of the main sources of freshwater in cold regions. The glacier melting process can significantly impact the glacier mass balance (GMB) and contribute a large amount of runoff in cold regions. This study applied the recently developed semi-distributed glacio-hydrological conceptual model (FLEXG) to understand the glacier melting process and the effect of topography on GMB in the Torne River basin, northern Sweden. The study simulated glacier and snow accumulation and ablation, as well as runoff from the glacier and non-glacier areas of the basin using the FLEXG model for the time period 1989–2018. The FLEXG model considers the influence of topography on runoff generation, and in this study the basin was classified into 143 zones depending on elevation and aspect. In order to gain a comprehensive view of the performance of the FLEXG model, the classical lumped hydrological model HBV was used and compared with the FLEXG model in simulating total streamflow and peak runoff at the outlet of the basin. Our results revealed that the FLEXG model performed well in reproducing the streamflow (also better than the HBV model) with metric Kling-Gupta Efficiency (KGE) of 0.80 and 0.71 for the calibration and validation periods, respectively. We also found that the FLEXG model performs better in peak runoff simulation than the HBV model. The FLEXG simulated snow cover area proportion agreed well with the MODIS satellite snow cover product (R2 = 0.60 and RMSE = 28%). The GMB in different elevation zones was simulated, and a downward trend was found for GMB changes during the study period because of climate change.

Spatial variability in Alpine reservoir regulation: deriving reservoir operations from streamflow using generalized additive models

Abstract. Reservoir regulation affects various streamflow characteristics, from low to high flows, with important implications for downstream water users. However, information on past reservoir operations is rarely publicly available, and it is hardly known how reservoir operation signals, i.e. information on when water is stored in and released from reservoirs, vary over a certain region. Here, we propose a statistical model to reconstruct reservoir operation signals in catchments without information on reservoir operation. The model uses streamflow time series observed downstream of a reservoir that encompass a period before and a period after a known year of reservoir construction. In a first step, a generalized additive model (GAM) regresses the streamflow time series from the unregulated pre-reservoir period on four covariates including temperature, precipitation, day of the year, and glacier mass balance changes. In a second step, this GAM, which represents natural conditions, is applied to predict natural streamflow, i.e. streamflow that would be expected in the absence of the reservoir, for the regulated period. The difference between the observed regulated streamflow signal and the predicted natural baseline should correspond to the reservoir operation signal. We apply this approach to reconstruct the seasonality of reservoir regulation, i.e. information on when water is stored in and released from a reservoir, from a dataset of 74 catchments in the central Alps with a known reservoir construction date (i.e. date when the reservoir went into operation). We group these reconstructed regulation seasonalities using functional clustering to identify groups of catchments with similar reservoir operation strategies. We show how reservoir management varies by catchment elevation and that seasonal redistribution from summer to winter is strongest in high-elevation catchments. These elevational differences suggests a clear relationship between reservoir operation and climate and catchment characteristics, which has practical implications. First, these elevational differences in reservoir regulation can and should be considered in hydrological model calibration. Furthermore, the reconstructed reservoir operation signals can be used to study the joint impact of climate change and reservoir operation on different streamflow signatures, including extreme events.

Recent 50-Year Glacier Mass Balance Changes over the Yellow River Source Region, Determined by Remote Sensing

The A’nyêmaqên Mountains have the largest concentration of glaciers in the Yellow River basin, which play a crucial role in regulating the runoff regime of the Yellow River. Thus, the quantification of glacier mass balance and its effects on river runoff is greatly required. However, current studies mainly focus on mass changes since 2000. Here, we report for the first time region-wide glacier elevation and mass changes, which were derived from digital elevation models (DEMs) produced from historical topographic maps (TOPO), SRTM retrievals, and ASTER L1A stereo imagery spanning the past 50 years. The results indicated a negative mass balance (−0.24 ± 0.05 m w.e. a−1) of all glaciers for the 1966–2018 timespan. The mass loss rapidly accelerated from −0.16 ± 0.09 m w.e. a−1 in 1966–2000 to −0.36 ± 0.06 m w.e. a−1 during the period from 2000–2018. The rise in mass loss rate from 2000 onwards was mainly associated with the rapidly increased summer warming.

ASSESSMENT OF GLACIER MASS BALANCE IN THE HIMALAYAN-KARAKORAM REGION

Mountain glaciers are susceptible to climate change. Most high-elevation glaciers, including the Himalayan glaciers, have been receding at an unprecedented rate in recent decades. Moreover, most mountain glaciers are found in the Himalayan areas, but field sampling and research efforts are limited due to logistical and financial constraints. From 1997 to 1999, just 6.8 km² of the 33,000 km² were examined in the Himalayan region. Previous studies indicated that Himalayan glaciers have been melting at an alarming rate over the past few decades. The objective of this paper is to review glacier changes, with an emphasis on mass balance changes in the Himalayan-Karakoram ranges, using 15 ISI journal articles published between 2008 and 2017. The acquired data on glacier mass balance was used to create a glacier mass balance change map for quantification using ArcGIS software and Landsat map as base map. The majority of the glaciers in the study area melted at various rates, with the most extensive glacier loss occurring in the west Himalayan highlands and the lowest occurring in the Karakoram region. Therefore, additional scientific research have to be conducted, and significant actions have to be taken at many different levels to prevent the continued loss of glaciers in this area.

Glacier Mass Balance Changes Over the Turgen Daban Range, Western Qilian Shan, From 1966/75 to 2020

Extensive efforts for quantifying regional glacier mass balance in the Qilian Mountains have been made using the geodetic method, but these estimations were rarely extended back to the period before 2000. This study presents glacier mass budgets in the Turgen Daban Range, over the western Qilian Mountain, from 1966/75 to 2020 by means of the digital elevation models generated by the topographic maps and ASTER images. The results show that the glacier mass decreased by −18.79 ± 12.48 m w.e. during the past 50 years. The average mass loss rate is estimated to be −0.19 ± 0.08 m w.e.a−1 for the 1966/75-2006 period and −0.45 ± 0.17 m w.e.a−1 during 2006–2020, respectively, suggesting a remarkable acceleration of glacier mass loss. This may be attributable to the significant increase in air temperature and the insignificant precipitation increase which cannot offset glacier melting caused by increased temperature. Due to the melting and shrinking of glaciers, the area of glacial lakes increases by 2.83 km2 from 1987 to 2020.

Glaciers of the Olympic Mountains, Washington—The Past and Future 100 Years

AbstractIn 2015, the Olympic Mountains contained 255 glaciers and perennial snowfields totaling 25.34 ± 0.27 km2, half of the area in 1900, and about 0.75 ± 0.19 km3 of ice. Since 1980, glaciers shrank at a rate of −0.59 km2 yr−1 during which time 35 glaciers and 16 perennial snowfields disappeared. Area changes of Blue Glacier, the largest glacier in the study region, was a good proxy for glacier change of the entire region. Modeled glacier mass balance, based on monthly air temperature and precipitation, correlates with glacier area change. The mass balance is highly sensitive to changes in air temperature rather than precipitation, typical of maritime glaciers. In addition to increasing summer melt, warmer winter temperatures changed the phase of precipitation from snow to rain, reducing snow accumulation. Changes in glacier mass balance are highly correlated with the Pacific North American index, a proxy for atmospheric circulation patterns and controls air temperatures along the Pacific Coast of North America. Regime shifts of sea surface temperatures in the North Pacific, reflected in the Pacific Decadal Oscillation (PDO), trigger shifts in the trend of glacier mass balance. Negative (“cool”) phases of the PDO are associated with glacier stability or slight mass gain whereas positive (“warm”) phases are associated with mass loss and glacier retreat. Over the past century the overall retreat is due to warming air temperatures, +0.7°C in winter and +0.3°C in summer. The glaciers in the Olympic Mountains are expected to largely disappear by 2070.

Variations in Glacier Runoff Contributed by the Increased Negative Mass Balance over the Last Forty Years in the Tien Shan Mountains

In the context of global warming, the melting of glaciers in the Tien Shan Mountains as the important “solid reservoir” in the arid area of Central Asia is accelerating in recent decades, leading to profound changes in regional water resources. Based on the simulated glaciological data from the Python Glacier Evolution Model (PyGEM) and the measured glaciological data from the World Glacier Monitoring Service (WGMS), this paper analyzed the applicability of simulated data, the changes in glacier mass balance, and the responses of the glacier to climate change and its impacts on glacier runoff in the Tien Shan Mountains. The results show that (1) the PyGEM simulation dataset is in good agreement with the measurements, which can effectively reproduce the change in the glacier mass balance in the Tien Shan Mountains glaciers and is suitable for studying the regional scale glacier change. (2) From 1980 to 2016, the decadal average mass balance change rate of glaciers in the Tien Shan Mountains was −0.012 m w.e. yr−1. The regional mass balance showed an overall negative increasing trend (the area with increasingly negative accounted for 80.13% of the entire area), with a positive increase that only occurred in the West Tien Shan Mountains and western North Tien Shan Mountains (19.87%). (3) The correlation between the temperature and mass balance is much higher than that between the precipitation and mass balance. Temperature dominates the change and development of regional glaciers. The increase in negative glacier mass balance that was observed in the study area is mainly affected by the rising temperature, the decreasing solid precipitation in the accumulation period, and the rapid melting in the ablation period. (4) The glacier runoff in the six representative rivers showed an increasing trend. The contribution rate of glacier runoff to river runoff changed significantly after 2000 but differed among rivers. Overall, the larger the glacier area in the source region is, the greater the contribution rate of glacier runoff is, and the more the contribution rate continuously increases or fluctuates; otherwise, the contribution rate keeps declining, which means the runoff peak may have passed and future runoff may decrease.

Glacier mass balance changes in Malan Mountain based on InSAR and LiDAR altimetry

Glacier mass balance changes in Malan Mountain based on InSAR and LiDAR altimetry

Estimating the Changes in Glaciers and Glacial Lakes in the Xixabangma Massif, Central Himalayas, between 1974 and 2018 from Multisource Remote Sensing Data

The continuous melting of valley glaciers can impact the water levels of glacial lakes and create glacial lake outburst floods (GLOFs). The Xixabangma massif is one of the most populated areas in the Himalayas and has suffered from multiple GLOFs. To estimate the glacier melting rate in the past four decades and analyze the outburst risk of glacial lakes in the Xixabangma massif, we determined changes in glacier mass balance, glacier area and glacial lake area based on KH-9 images, TanDEM-X images, Landsat images, SRTM DEM and ICESat-2 elevations. Our results show that, from 1974 to 2018, the total glacier area shrank from 954.01 km2 to 752.46 km2, whereas the total glacial lake area grew from 20.90 km2 to 38.71 km2. From 1974 to 2000, 2000 to 2013 and 2013 to 2018, the region-wide glacier mass balance values were −0.16 m w.e./a, −0.31 m w.e./a and −0.29 m w.e./a, respectively. Three glacial lakes, named Gangxico, Galongco and Jialongco, respectively, expanded by 127.14%, 373.45% and 436.36% from 1974 to 2018, and the mass loss rates of their parent glaciers from 2000 to 2013 increased by 81.72%, 122.22% and 160.00% relative to those during 1974 to 2000. The dams of these three lakes are unstable, and their drainage valleys directly connect to a major town and its infrastructure. Due to current high-water levels, possible external events such as ice collapse, landslide, heavy rainfall and earthquakes can easily trigger GLOFs. Hence, we deemed that the Gangxico, Galongco and Jialongco glacial lakes are dangerous and require special attention.

High-Resolution Monitoring of Glacier Mass Balance and Dynamics with Unmanned Aerial Vehicles on the Ningchan No. 1 Glacier in the Qilian Mountains, China

Glaciers located in the Qilian Mountains are rapidly retreating and thinning due to climate change. The current understanding of small glacier mass balance changes under a changing climate is limited by the scarcity of in situ measurements in both time and space as well as the resolution of remote sensing products. Unmanned aerial vehicles (UAVs) provide an unparalleled opportunity to track the spatiotemporal variations in glacier extent at a high resolution and the changing glacier morphological features related to glacial dynamics. Five measurements were performed on the Ningchan No. 1 (NC01) glacier in the Qilian Mountains between 18 August 2017 and 13 August 2020. The glacier changes displayed in the digital orthophoto maps (DOMs) and digital surface models (DSMs) show a 7.4 ± 0.1 m a−1 retreat of the terminus of NC01, a mass balance of −1.22 ± 0.1 m w.e. a−1 from 2017 to 2020, and a maximum surface velocity of 3.2 ± 0.47 m from 18 August 2017 to 26 August 2018, which clearly show consistency with stake measurements. The surface elevation change was influenced by the combined effects of air temperature, altitude, slope, and surface velocity. This research demonstrates that UAV photogrammetry can greatly improve the temporal and spatial resolution of glaciological research.

Local- and Regional-Scale Forcing of Glacier Mass Balance Changes in the Swiss Alps

Glacier mass variations are climate indicators. Therefore, it is essential to examine both winter and summer mass balance variability over a long period of time to address climate-related ice mass fluctuations. In this study, we analyze glacier mass balance components and hypsometric characteristics with respect to their interactions with local meteorological variables and remote large-scale atmospheric and oceanic patterns. The results show that all selected glaciers have lost their equilibrium condition in recent decades, with persistent negative annual mass balance trends and decreasing accumulation area ratios (AARs), accompanied by increasing air temperatures of ≥ +0.45 °C decade−1. The controlling factor of annual mass balance is mainly attributed to summer mass losses, which are correlated with (warming) June to September air temperatures. In addition, the interannual variability of summer and winter mass balances is primarily associated to the Atlantic Multidecadal Oscillation (AMO), Greenland Blocking Index (GBI), and East Atlantic (EA) teleconnections. Although climate parameters are playing a significant role in determining the glacier mass balance in the region, the observed correlations and mass balance trends are in agreement with the hypsometric distribution and morphology of the glaciers. The analysis of decadal frontal retreat using Landsat images from 1984 to 2014 also supports the findings of this research, highlighting the impact of lake formation at terminus areas on rapid glacier retreat and mass loss in the Swiss Alps.

Accelerated glacier mass loss in the largest river and lake source regions of the Tibetan Plateau and its links with local water balance over 1976–2017

AbstractVariations in glacier meltwater in the source regions of the Tibetan Plateau's (TP) largest lake (Selin Co) and China's longest river (Yangtze River) regulate the local and downstream water balance under the warming climate. However, the magnitude of their variations over the past four decades is still unknown. Here, we examine long-term changes in glacier mass balance over 1976–2017 using KH-9 and CoSSC-TanDEM-X data. We find that the mean rate of glacier mass loss (GML) has accelerated from −0.21 ± 0.11 m a–1over 1976–2000, to −0.28 ± 0.14 m a–1over 2000–11, and subsequently to −0.48 ± 0.10 m a–1over 2011–17. Changes in temperature and precipitation are the major causes of GML. Over 1976–2017, the contribution of decadal GML to Tuotuohe sub-basin runoff ranges from 4.3 to 8.0%, while its contribution to increased lake volume change in Selin Co and Chibzhang Co-Dorsoidong Co ranges from 3.5 to 16.3% and 19.2 to 21.4%, respectively. The GML of source regions made relatively small contributions to river runoff and lake supply, but plays a vital role when precipitation decreases. The quantitative evaluation of the water balance for the sources of great rivers and lakes over the TP is therefore important for water resource management and hydrological cycle studies.

Simulating glacier mass balance in the cross-border Poiqu/Bhotekoshi Basin, China and Nepal

Abstract To assess the change of glacier mass balance (GMB) in the Poiqu/Bhotekoshi basin in the context of global warming, this study applied a conceptual Hydrologiska Bryans Vattenbalansavdelning (HBV) hydrological model to quantify the GMB in the area. The HBV model was trained and validated based on in-situ hydro meteorological data from 10 weather stations in the basin. The dataset, which consists of the daily observations for both rainfall and air temperature, was partitioned into two decades, 1988–1998 and 1999–2008 for calibration and validation, respectively. The calibrated model was adopted to restore the daily runoff depth and then estimate the annual changes of GMB in Poiqu/Bhotekoshi basin over the period of 1988–2008. Results show that the Nash–Sutcliffe efficiency coefficient (Reff) of the daily runoff depth simulation after the runoff calibration process was above 0.802. Therefore, the simulated values of the HBV model are reliable and can be used to estimate the GMB of Himalayan cross-border glacial mountain basins with huge elevation difference, and provide scientific data support for water resources management. Furthermore, the result demonstrated a slow year-by-year rise of snow water equivalent because of global warming, and it highly correlates with the soil moisture, the spring temperature and the summer precipitation.

Assessing glacier retreat and its impact on water resources in a headwater of Yangtze River based on CMIP6 projections

Glacier retreat caused by global warming alters the hydrological regime and poses far-reaching challenges to water resources and nature conservation of the headwater of Yangtze River, and its vast downstream regions with dense population. However, there is still lack of a robust modeling framework of the “climate-glacier-streamflow” in this water tower region, to project the future changes of glacier mass balance, glacier geometry, and the consequent impacts on runoff. Moreover, it is imperative to use the state-of-the-art sixth phase Coupled Model Intercomparison Project (CMIP6) to assess glacio-hydrology variations in future. In this study, we coupled a glacio-hydrological model (FLEXG) with a glacier retreat method (Δh-parameterization) to simulate glacio-hydrological processes in the Dongkemadi Glacier (over 5155 m.a.s.l), which has the longest continuous glacio-hydrology observation on the headwater of Yangtze River. The FLEXG-Δh model was forced with in-situ observed meteorological data, radar ice thickness, remote sensing topography and land cover data, and validated by measured runoff. The results showed that the model was capable to simulate hydrological processes in this glacierized basin, with Kling-Gupta efficiency (IKGE) of daily runoff simulation 0.88 in calibration and 0.70 in validation. Then, forcing by the bias-corrected meteorological forcing from the eight latest CMIP6 Earth system models under two climate scenarios (RCP2.6 and RCP8.5), we assessed the impact of future climate change on glacier response and its hydrological effects. The results showed that, to the end of simulation in 2100, the volume of the Dongkemadi Glacier would continuously retreat. For the RCP2.6 and RCP8.5 scenarios, the glacier volume will decrease by 8.7 × 108 m3 (74%) and 10.8 × 108 m3 (92%) respectively in 2100. The glacier runoff will increase and reach to peak water around 2060 to 2085, after this tipping point water resources will likely decrease.

A doubling of glacier mass loss in the Karlik Range, easternmost Tien Shan, between the periods 1972–2000 and 2000–2015

AbstractDespite a number of studies reporting glacier extent changes and their response to climate change over the eastern Tien Shan, glacier mass-balance changes over multiple decades are still not well reconstructed. Here, glacier mass budgets on the Karlik Range, easternmost Tien Shan during the time spans of 1972–2000 and 2000–2015 are quantified using digital elevation models reconstructed from topographic maps, SRTM X-band radar data and ASTER images. The results exhibit significant glacier mass loss in the Karlik Range for the two time spans, with a mean mass loss of −0.19 ± 0.08 m w.e. a−1 for the 1972–2000 period and −0.45 ± 0.17 m w.e. a−1 for the 2000–2015 period. The doubling of mass loss over the latter period suggests an acceleration of glacier mass loss in the early 21st century. The accelerated mass loss is associated with regional warming whereas the decline in annual precipitation is not significant.

The response of runoff components and glacier mass balance to climate change for a glaciated high-mountainous catchment in the Tianshan Mountains

Glaciers are important freshwater storage systems in the Tianshan Mountains. Under the context of climate change, quantifying changes in glacier mass balance, the melt-season (June–September) runoff and its key runoff component (glacier runoff) is of importance for understanding the discharge composition and ensuring adequate management of water resources. In this study, the modified HBV-D (Hydrologiska Byrans Vattenbalansavdelning-D) hydrological model was used to simulate hydrological processes for a data-sparse glacierized watershed, the headwater catchment of Manas River basin (MRB) in the Tianshan Mountains. Meanwhile, the roles of three modified elements of HBV-D in simulating glacier dynamics are identified. Sequently, the glacier mass balance and runoff during 1984–2006 are reconstructed and their responses to climate change are investigated. The analysis showed (1) the snow/glacier melt method makes more contribution to improving the performance of HBV-D model in simulating historical change of glacier volume, followed by the glacier dynamic method. (2) The reconstructed mass balance follows a decreased trend in the MRB. The maximum accumulation of glacier mass balance occurs in June. Snowmelt over the surface of glacier and glacier melt reach peak in June and August, respectively. Furthermore, sensitivity experiments showed increased mass balance induced by a 10% increase in precipitation cannot compensate for the decreased mass balance due to a 1 °C temperature rise. (3) Significant contribution (about 41.5%) of runoff in glacierized area to the melt-season total runoff of the catchment is identified. Both the glacier runoff and its contribution to melt-season total runoff show increased trends during the simulation period. Compared with the melt-season mean temperature and annual precipitation over glaciers, the melt-season positive accumulated temperature over glaciers played the most important role in influencing changes in glacier runoff in MRB. The findings in this study are beneficial for implementing adaptive countermeasures for water resources management in the data-scarce glaciated high-mountainous region.