Study region: The Urumqi River basin located in eastern Tien Shan in Central Aisa Study focus: Glacier runoff plays a pivotal role in water resources and stabilizing streamflow in mountainous regions. To assess the characteristics of glacier ice melt runoff in sub-basins within a single basin, three sub-basins with glacier ratios varying from 4% to 46% in the Urumqi River basin are investigated. Through the simulation by HBV light model on the basis of the observed meteorological and hydrological data. The characteristics and behaviour of glacier ice melt runoff in the three sub-basins are analysed. New hydrological insights for the region: It was found that both the contribution ratios of ice melt runoff and glacier runoff increase linearly with the increasing glacier ratio for the three catchments, rather than logarithmically or exponentially as observed in previous studies. This is due to the relatively high contributions of ice melt and glacier runoff to river flow in a catchment characterized by high elevation and extensive glacier coverage (Catchment 1), resulting from the coincidence of summer precipitation maxima with snow and ice melt in this region. The coefficient of variations (CV) of river flow tends to decrease with the decreasing glacier ratio in subbasins in the Urumqi River basin, indicating that river flow becomes more stable as it flows farther from the headwater in the Urumqi River basin. The lowest glacierized Catchment 3 exhibited the minimum CV value, demonstrating a stable outflow.

To address data scarcity on long-term glacial discharge and inadequacies in simulating and predicting hydrological processes in the Tien Shan, this study analysed the observed discharge at multiple timescales over 1980s-2017 and projected changes within a representative glacierized high-mountain region: eastern Tien Shan, Central Asia. Hydrological processes were simulated to predict changes under four future scenarios (SSP1, SSP2, SSP3, and SSP5) using a classical hydrological model coupled with a glacier dynamics module. Discharge rates at annual, monthly (June, July, August) and daily timescales were obtained from two hydrological gauges: Urumqi Glacier No.1 hydrological station (UGH) and Zongkong station (ZK). Overall, annual and summer discharge increased significantly ( p < 0.05) at both stations over the study period. Their intra-annual variations mainly resulted from differences in their recharge mechanisms. The simulations show that a tipping point in annual discharge at UGH may occur between 2018 and 2024 under the four SSPs scenarios. Glacial discharge is predicted to cease earlier at ZK than at UGH. This relates to glacier type and size, suggesting basins with heavily developed small glaciers will reach peak discharge sooner, resulting in an earlier freshwater supply challenge. These findings serve as a reference for research into glacial runoff in Central Asia and provide a decision-making basis for planning local water-resource projects.

The detailed physical processes involved in slowing glacier ablation by material cover remain poorly understood so far. In the present study, using the snow cover model SNOWPACK, the effect of geotextile cover on the energy and mass balance at the tongue of the Urumqi Glacier No. 1 (Chinese Tien Shan) was simulated between July 12, 2022 and August 31, 2022. The mass changes and the energy fluxes with and without material cover were compared. The results indicated that the geotextile covering reduced glacier ablation by approximately 68% compared to the ablation in the uncovered regions. The high solar reflectivity of the geotextile reduced the net short-wave radiation energy available for the melt by 45%. Thermal insulation of the geotextile reduced the sensible heat flux by 15%. In addition, the wet geotextile exerted a cooling effect through long-wave radiation and negative latent heat flux. This cooling effect reduced the energy available for ablation by 20%. Consequently, only 37% of the energy was used for melting compared to that used in the uncovered regions (67%). Sensitivity experiments revealed that the geotextile cover used at a thickness range of 0.045-0.090 m reduced the ice loss by approximately 68%-72%, and a further increase in the thickness of the geotextile cover led to little improvements. A higher temperature and greater wind speed increased glacier ablation, although their effects were small. When the precipitation was set to zero, it led to a significantly increased melt. Overall, the geotextile effectively protected the glacier tongue from rapid melting, and the observed results have provided inspiration for developing an effective and sustainable approach to protect the glaciers using geotextile cover.

Glacier mass balance and its sensitivity to climate change depend to a large degree on the albedo and albedo feedback. Although recent increasing studies reconstruct the annual surface mass balance (SMB) based on the relationships between satellite-derived minimum albedo and annual glaciological mass balance (so-called albedo method), a relationship remains conjectural for Tien Shan glaciers. Accumulation and ablation occur simultaneously in summer, causing different surface processes. We examine this relationship using glaciological mass-balance data and the equilibrium-line altitude (ELA) made on the eastern branch of Urumqi Glacier No. 1 (UG1-E), Tuyuksu, Golubin and Glacier No. 354, and ablation-season (May-September) albedo retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2000 to 2021. Compared with minimum ablation-season albedo, we find higher coefficients of determination between mean ablation-season albedo and glaciological mass balance at UG1-E and Tuyuksu. In contrast, for Golubin and Glacier No. 354, glaciological mass balance is higher correlated to minimum ablation-season albedo than mean ablation-season albedo. This difference is related to the glaciological mass-balance time period. The relationship between albedo and glaciological mass balance is obtained over a shorter time for Golubin (8 years) and Glacier No. 354 (9 years) than for UG1-E (20 years) and Tuyuksu (20 years). Nonetheless, based on the correlativity between MODIS-derived mean ablation-season albedo and minimum ablation-season albedo and glaciological mass balance of Golubin and Glacier No. 354 over the 2011-2019 period, the annual SMB for these glaciers can be reconstructed using the albedo method over the period 2000-2010. Comparison with previously reconstructed results indicated that the mass balance derived from albedo is robust for Glacier No. 354, while for Golubin, the results derived from the albedo method only captured the relative changes in mass balance. The current study suggested that ablation-season albedo can be regarded as a proxy for annual mass balance, and mean ablation-season albedo may be more reliable than minimum ablation-season albedo for some Tien Shan glaciers.

Surface albedo exerts substantial control over the energy available for glacier melting. For Urumqi Glacier No.1 in the Tien Shan Mountains, China, represented as a summer accumulation glacier, the variations in albedo driven by surface processes are complex and still poorly understood. In this study, we examined the interannual trends in ablation-period albedo from 2000 to 2021 using MOD10A1 products, evaluated the variation in bare-ice albedo retrieved from 13 end-of-summer Landsat images obtained between 2002 and 2019, and investigated the seasonal variation and diurnal cycle of surface albedo collected near the equilibrium line of the glacier by an AWS from September 2018 to August 2021. During the period of 2000-2021, the average ablation-period albedo presented a slight but not statistically significant downward trend, with a total decrease of 1.87%. Specifically, the decrease in glacier albedo was quicker in July than that in August, and there was a slight increase in May and June. The blackening phenomenon was shown on the east branch glacier, but not on the west branch glacier. For seasonal variability, a bimodal pattern was demonstrated, different from the unimodal seasonal variation in other midlatitude glaciers. The albedo peaks occurred in December and April or May. Under clear sky conditions, the diurnal cycle presented three patterns: a symmetric pattern, an asymmetric pattern, and a progressive decreasing pattern. Air temperature and solid precipitation are the main drivers of variations in glacier albedo, but in different periods of the ablation season, two climate variables affect albedo to varying degrees. The effect of surface albedo reduction enhanced glacier melting by about 20% over the past 20 years. The short-term increase in albedo caused by summer snowfall can considerably reduce glacier melting by as much as 80% in June.

Artificial glacier melt reduction is gaining increasing attention because of rapid glacier retreats and the projected acceleration of future mass losses. However, quantifying the effect of artificial melt reduction on glaciers in China has not been currently reported. Therefore, the case of Urumqi Glacier No.1 (eastern Tien Shan, China) is used to conduct a scientific evaluation of glacier cover efficiency for melt reduction between 24 June and 28 August 2021. By combining two high-resolution digital elevation models derived from terrestrial laser scanning and unmanned aerial vehicles, albedo, and meteorological data, glacier ablation mitigation under three different cover materials was assessed. The results revealed that up to 32% of mass loss was preserved in the protected areas compared with that of the unprotected areas. In contrast to the unprotected glacier surface, the nanofiber material reduced the glacier melt by up to 56%, which was significantly higher than that achieved by geotextiles (29%). This outcome could be attributed to the albedo of the materials and local climate factors. The nanofiber material showed higher albedo than the two geotextiles, dirty snow, clean ice, and dirty ice. Although clean snow had a higher albedo than the other materials, its impact on slowing glacier melt was minor due to the lower snowfall and relatively high air temperature after snowfall in the study area. This indicates that the efficiencies of nanofiber material and geotextiles can be beneficial in high-mountain areas. In general, the results of our study demonstrate that the high potential of glacier cover can help mitigate issues related to regions of higher glacier melt or lacking water resources, as well as tourist attractions.

Hanging glaciers hold the absolute dominant number in West China and their changes had important influences on local hydrology, sea-level rise and natural hazards (snow/ice avalanches). However, logistic and operational difficulties have resulted in the lack of in-situ-measured data, leaving us with poor knowledge of the changing behaviors of this type of glacier. Here, we presented the spatiotemporal pattern of seasonal and annual mass changes of a mid-latitude hanging glacier in the Tien Shan based on repeated terrestrial laser scanning (TLS) surveys during the period 2016-2018. The distributed glacier surface elevation changes exhibited highly spatiotemporal variability, and the winter elevation changes showed slight surface lowering at the upper elevations and weak thickening at the glacier terminus, which was contrary to altitudinal elevation changing patterns at the summer and annual scales. Mass balance processes of the hanging glacier mainly occurred during summer and the winter mass balance was nearly balanced (-0.10 +/- 0.15 m w.e.). The glacier exhibited more rapid mass loss than adjacent other morphological glacier and the estimated response time of the glacier to climate change was very short (6-9 years), indicating hanging glaciers will experience rapid wastage and disappearance in the future even with climate change mitigation.

The eastern Tien Shan hosts substantial mid-latitude glaciers, but in situ glacier mass balance records are extremely sparse. Haxilegen Glacier No. 51 (eastern Tien Shan, China) is one of the very few well-measured glaciers, and comprehensive glaciological measurements were implemented from 1999 to 2011 and re-established in 2017. Mass balance of Haxilegen Glacier No. 51 (1999-2015) has recently been reported, but the mass balance record has not extended to the period before 1999. Here, we used a 1:50,000-scale topographic map and long-range terrestrial laser scanning (TLS) data to calculate the area, volume, and mass changes for Haxilegen Glacier No. 51 from 1964 to 2018. Haxilegen Glacier No. 51 lost 0.34 km(2) (at a rate of 0.006 km(2) a(-1) or 0.42% a(-1)) of its area during the period 1964-2018. The glacier experienced clearly negative surface elevation changes and geodetic mass balance. Thinning occurred almost across the entire glacier surface, with a mean value of -0.43 +/- 0.12 m a(-1). The calculated average geodetic mass balance was -0.36 +/- 0.12 m w.e. a(-1). Without considering the error bounds of mass balance estimates, glacier mass loss over the past 50 years was in line with the observed and modeled mass balance (-0.37 +/- 0.22 m w.e. a(-1)) that was published for short time intervals since 1999 but was slightly less negative than glacier mass loss in the entire eastern Tien Shan. Our results indicate that Riegl VZ (R)-6000 TLS can be widely used for mass balance measurements of unmonitored individual glaciers.

Light-absorbing impurities on glaciers are important factors that influence glacial surface albedo and accelerate glacier melt. In this study, the quantity of light-absorbing impurities on Keqikaer Glacier in western Tien Shan, Central Asia, was measured. We found that the average concentrations of black carbon was 2,180 ng/g, with a range from 250 ng/g to more than 10,000 ng/g. The average concentrations of organic carbon and mineral dust were 1,738 ng/g and 194 mu g/g, respectively. Based on simulations performed with the Snow Ice Aerosol Radiative model simulations, black carbon and dust are responsible for approximately 64% and 9%, respectively, of the albedo reduction, and are associated with instantaneous radiative forcing of 323.18 W/m(2) (ranging from 142.16 to 619.25 W/m(2)) and 24.05 W/m(2) (ranging from 0.15 to 69.77 W/m(2)), respectively. For different scenarios, the albedo and radiative forcing effect of black carbon is considerably greater than that of dust. The estimated radiative forcing at Keqikaer Glacier is higher than most similar values estimated by previous studies on the Tibetan Plateau, perhaps as a result of black carbon enrichment by melt scavenging. Light-absorbing impurities deposited on Keqikaer Glacier appear to mainly originate from central Asia, Siberia, western China (including the Taklimakan Desert) and parts of South Asia in summer, and from the Middle East and Central Asia in winter. A footprint analysis indicates that a large fraction (>60%) of the black carbon contributions on Keqikaer Glacier comes from anthropogenic sources. These results provide a scientific basis for regional mitigation efforts to reduce black carbon.

The Tien Shan Mountains, the largest mountain range in the Xinjiang Autonomous Region of north-western China, significantly influence the climate of central Asia. Recent permafrost changes in the region of the headwaters of the Urumqi River, as well as its relationship to climatic factors, were studied based on ground temperatures measured in a 60 m deep borehole, air temperatures and precipitation over a period from 1992 to 2011. The results showed that the maximum active-layer thickness (ALT; 1.70 m) occurred in 2009 and 2011, with an increase of 0.45 m compared with 1992. The change in ALT was related to the variation in the climatic conditions, and the increase in the deep-seated permafrost temperature. The permafrost temperature increased from -1.7 degrees C in 1992 to -1.1 degrees C in 2011, and the permafrost base moved upwards by approximately 14 m from 1992 to 2011. The long-term step-wise change in the air temperature may be the main cause of the permafrost warming in the headwaters of the Urumqi River. Copyright (c) 2015 John Wiley & Sons, Ltd.