Urumqi Glacier Research Articles

Influence of Sub-Cloud Secondary Evaporation Effects on the Stable Isotopes in Precipitation of Urumqi Glacier No. 1, Eastern Tianshan

Influence of Sub-Cloud Secondary Evaporation Effects on the Stable Isotopes in Precipitation of Urumqi Glacier No. 1, Eastern Tianshan

Heatwaves in summer 2022 forces substantial mass loss for Urumqi Glacier No. 1, China

Abstract Extreme heat events in the summer of 2022 were observed in Eurasia, North America and China. Glaciers are a unique indicator of climate change, and the European Alps experienced substantial glacier mass loss as a result of the conditions in 2022, which prompted a wide range of community concerns. However, relevant findings for glaciers in China have not been currently reported. Here, we document the response of Urumqi Glacier No. 1 in the eastern Tien Shan to the extreme heat observed in 2022 based on in situ measurements that span more than 60 years. In 2022, Urumqi Glacier No. 1 exhibited the second largest annual mass loss on record, and the summer mass balance was the most negative on record. The hottest summer on record and relatively lower solid precipitation ratio contributed to the exceptional mass losses at Urumqi Glacier No. 1 in 2022, demonstrating the significant influence of heatwaves on extreme glacier melt in China.

Hydrological response to climate change in a glacierized catchment in eastern Tien Shan, Central Asia

Study regionThe headwaters of Urumqi River basin located in eastern Tien Shan Study focusGlacier shrinkage in recent decades has caused the volume and timing of glacier-fed streamflow to change, which in turn has significantly impacted the water supply and ecological system in the vast arid land in Central Asia and drawn wide public attention. Based on a glacio-hydrologic degree-day model, the runoff mechanisms and processes of the glacier-fed catchment are revealed. New hydrological insights for the regionThe study found that about 51 % glacier coverage of the Urumqi Glacier No.1 catchment (UG1C) generates approximately 76 % glacier runoff, indicating that glacier melt comprises a significant water resource in the region. The different ways that the glacier melts in response to temperature versus precipitation on a daily scale by changing glacier mass balance can effectively stabilize streamflow, showing a strong capacity of the glacier to naturally adjust streamflow beneficially to water utilization by those downstream. Based on the sensitivity of modelled runoff to glacier change by comparing simulations using constant glacier cover that accommodated dynamic changes in glacier area, we found that the maximum volume of ice melt runoff during the past four decades appeared during the period 1996–2019, most likely around 2010.

Rapid mass losses of Urumqi River Basin glaciers, eastern Tianshan Mountains revealed from multi-temporal DEMs, 1964–2021

ABSTRACT Glacier volume changes have remarkable impacts on regional water resources; however, their estimation uncertainties remain large. In this study, the surface elevations of seven glaciers at the headwaters of the Urumqi River exhibited obvious thinning at the rate of 0.32 m a−1 from 1964 to 2021. Correlations between the ice volume change (dV) derived from surface elevation conversion and the area change (dS) were established for valley, cirque, and hanging glaciers. The ice volumes of valley, cirque, and hanging glaciers in the Urumqi River Basin decreased by 0.99 km3, 0.18 km3, and 0.59 km3, respectively, and the total ice volume decreased by 1.76 km3 during 1964–2021. Ice volume losses are accelerating. The correlation between dV and dS for valley glaciers produced a large estimation difference for the ice volume change of Urumqi Glacier No. 1 (UG1) compared with the glaciological mass balance (15%), while the estimation differences of ice volume changes for the three types of glaciers in the Urumqi River Basin were within acceptable limits (10%) based on the geodetic results. This new method has vast potential in estimating ice volume changes at the basin or regional scale, or even across western China.

Occurrence, distribution, potential sources, and risks of organophosphate esters in fresh snow on Urumqi Glacier No. 1, eastern Tien Shan, China

Organophosphate esters (OPEs), extensively used as flame retardants, are widely detected in various regions and environments. The potential toxicity of OPEs has caused great concern in recent years. Based on the global distillation model, the Tien Shan glaciers, such as Urumqi Glacier No. 1, could be as a potential “sink” for OPEs. However, little is known about the concentration, distribution, potential sources, and ecological risks of OPEs in Tien Shan glaciers. In this study, fresh snow samples were collected at various altitudes on the Urumqi Glacier No. 1, eastern Tien Shan, China. The total concentrations of ten OPEs (Σ10OPEs) ranged from 116 to 152 ng/L. The most abundant OPE was tris-(2-chloroisopropyl) phosphate (TCIPP), contributing to 74 % of the total OPEs. Σ10OPEs, tri-n-butyl phosphate (TnBP), and TCIPP concentrations showed positive correlations with altitude, indicating the effect of cold condensation on OPEs deposition. Based on air mass back-trajectory analysis and principal component analysis, we found that emissions from both traffic and household products in indoor environment were the important sources, and OPEs on the Urumqi Glacier No. 1 might mainly originate from Europe. Our assessment also showed triphenyl phosphate (TPhP) posed a low ecological risk in snow. This is the first systematic study of OPEs on the Tien Shan glaciers.

Geotextile protection of glacier: Observed and simulated impacts on energy and mass balance

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.

Modeling the impact of climate change on streamflow in glacier/snow-fed northern Tianshan basin

Study regionUrumqi River headwater region in eastern Tianshan, central Asia. Study focusClimate change is anticipated to accelerate glacier shrinkage and alter hydrological conditions, causing variations in the runoff patterns in the catchment and significantly threatening the regional water resources. However, few models exhibit adequate performance to simulate both surface alterations and glacier/snow runoff. Therefore, this study combined the glacier module with the Soil and Water Assessment Tool (SWAT) model to estimate the effect of climate change on the streamflow in the Urumqi River headwater region. The Urumqi River Headwater region is representative because of its long data series, viatal location, and local water availability, and it contains the longest-observed reference glacier (Urumqi Glacier No.1) in China, which spans the period from 1958 to the present. New hydrological insights for the regionThe SWAT model performed satisfactorily for both calibration (1983–2005) and validation (2006–2016) periods with a Nash-Sutcliffe efficiency (NSE) greater than 0.80. The water balance analysis suggested that the snow/glacier melt contributed approximately 25% to the water yield. At the end of the 21st century, the temperature would increase by 2.4–3.8 °C while the precipitation would decrease by 1–2% under two future scenarios (ssp245 and ssp585). Thus, a 34–36% reduction in streamflow was projected due to above climate change impacts. This information would contribute to the development of adaptation strategies for sustainable water resource management.

Use of ablation-season albedo as an indicator of annual mass balance of four glaciers in the Tien Shan

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). Non-etheless, 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.

Source characteristics of icequakes caused by surface crevasses on Urumqi Glacier No. 1, Tianshan, China

SUMMARYIcequakes associated with crevassing provide key information on stress fields and water flow pathways inside glaciers, conditions which are sensitive to temperature and precipitation. In this study, we analyse seismic data from 321 days recorded by five broad-band seismometers on Urumqi Glacier No. 1, Tianshan, China, to investigate the source characteristics of icequakes. We first apply a multidimensional autoregressive maximum-likelihood algorithm to detect 12 template events from 62 days of continuous waveform data. The centroid locations of the 12 template events are located using a grid-search approach. We then obtain a catalogue of 41 895 icequakes by compiling all seismic data through a template-matching method. The local magnitudes of all icequakes range between −3.3 and 0.5, with a completeness magnitude of −2.95 and Gutenberg–Richter b-value of 1.08. The particle motion and frequency contents of the 12 template events show that the dominant phases on the vertical component are Rayleigh waves at 5–40 Hz, suggesting that these icequakes were generated by near-surface crevasses. The average daily icequake number for each month and diurnal icequake variations show clear seasonal features. The icequakes may be related to growth of the surface crevasses due to additional melting water and precipitation in summer and to the thermal contraction of the ice body in winter.

QMEC-based Analysis of the Soil Microbial Functional Potentials across Different Tibetan Plateau Glacier Forelands

Soil microorganisms dominate the biogeochemical cycles of elements in glacier forelands, which continue to expand due to the climate warming. We analyzed the soil microbial functional characteristics among three types of glacier forelands on the Tibetan Plateau: Yulong Glacier (Y), a temperate glacier; Tianshan Urumqi Glacier No.1 (T), a sub-continental glacier; and Laohugou Glacier No.12 (L), a continental glacier. Here, soil microbial functional genes were quantified using quantitative microbial element cycling technology (QMEC). We found that, in the three glacier forelands, the abundances of soil microbial functional genes related to hemicellulose degradation and reductive acetyl-CoA pathway were highest compared with other carbon-related functional genes. The main nitrogen cycling genes were involved in ammonification. The functional genes of the phosphorus cycle and sulfur cycle were related to organic phosphate mineralization and sulfur oxidation. Furthermore, the soils of the temperate glacier foreland with better hydrothermal conditions had the most complex microbial functional gene structure and the highest functional potentials, followed by those of the soils of continental glacier foreland with the driest environment. These significant differences in soil microbial functional genes among the three types of glacier forelands verified the impacts of geographic difference on microbial functional characteristics, as well as providing a basis for the study of soil microbial functions and biogeochemical cycles in glacier forelands.

Summertime surface mass balance and energy balance of Urumqi Glacier No. 1, Chinese Tien Shan, modeled by linking COSIMA and in-situ measured meteorological records

To get a better overview of atmosphere-driven mass changes at Urumqi Glacier No.1, Chinese Tien Shan, the surface energy budget and mass balance is modeled by linking the COupled Snowpack and Ice surface energy and MAss balance model (COSIMA) with in-situ measured meteorological records for the ablation period in 2018. The COSIMA is calibrated by manual optimization and the modeled results agree well with the in-situ surface temperature, snow height and seasonal mass balance. Our results reveal that Urumqi Glacier No.1 experienced a significant mass loss, with an average value of − 0.77 m w.e. over the ablation period 2018. The surface energy budget components can be classified into two categories: radiation (shortwave and longwave) and turbulent fluxes. Surface melt and solid precipitation were dominated components of mass balance. The COSIMA can reproduce the glaciological mass balance compared with other models. Sensitivity analysis showed that the mass balance was more sensitive to the temperature than precipitation, and mass loss caused by temperature increase of 1 K needed to be compensated by at least 40% precipitation increase. Air temperature during the ablation period was more important than annual precipitation in controlling mass balance changes on Urumqi Glacier No. 1. These findings will enhance our understanding of the mechanisms underlying mass balance processes of ablation period and their contribution to the acceleration of glacier retreat in Tien Shan.

Comparison of deep learning models and a typical process-based model in glacio-hydrology simulation

Glacier hydrology has profound implications for socio-economic development and nature conservation in arid Central Asia. Process-based hydrological models, which are the traditional tools used to simulate glacier melting, have made considerable contributions to advance our understanding of glacio-hydrology. Simultaneously, deep learning (DL) models have achieved excellent performance in many complex tasks and provide high accuracy. However, it is uncertain whether glacio-hydrological studies can benefit from the application of DL models. In this study, to help us assess water resource change for glacier-influenced regions, we used DL models to simulate glacio-hydrological processes in the Urumqi Glacier No. 1 in northwest China. First, we proposed a newly DL model called Exogenous Regularization Network (ERNet), which focuses on the relationship between exogenous (temperature and precipitation) and endogenous (runoff) variables, balancing the roles of different variables in the simulation process. Second, we compared ERNet with a stacked long short-term memory (LSTM) model and a process-based glacio-hydrology model, FLEXG. Experiments showed that compared with the other two models, ERNet not only performed well in runoff and peak flow simulations but also displayed superior transferability. Third, given that the DL model is data-driven, we experimentally compared the importance of air temperature and precipitation to glacial runoff processes. The results show that air temperature plays a dominant role in glacier runoff generation. We believe that the proposed model provides a useful predictive tool and that the results shed light on the future implication in cold region hydrology.

Study on Change of the Glacier Mass Balance and Its Response to Extreme Climate of Urumqi Glacier No.1 in Tianshan Mountains in Recent 41 Years

Glaciers are susceptible indicators of climate change and crucial parts of the world’s water cycle. In the context of global warming, we took the Urumqi Glacier No.1 (UG1) as an example, which is situated at the source of the Urumqi River on the northern slope of the Tianshan Mountains, Xinjiang, combined with the climate data of Daxigou Meteorological Station from 1980 to 2020, and the change of glacier mass balance and its response to extreme climate are discussed. The results suggest that the glacier mass balance of UG1 showed a downward trend over the studied 41-year period, and the mass loss increased. The cumulative glacier mass balance value was −19,776 mm w.e., and the average annual value was −482 mm w.e.a−1. The Mann-Kendall trend test showed that the change point occurred around 1994, and the mass balance of UG1 became more negative after 1994. In the same period, the changing mass balance trend of UG1 was not the same in different seasons. The inter-annual variation of summer mass balance was drastic, showing a marked downward trend; the inter-annual change of winter mass balance was small, showing a slight uptrend. The changing of extreme climate indices where UG1 is located showed that only TX90p and TX10p changed observably from 1980 to 2020, and the extreme precipitation indices changed evidently and had been on the rise. The changing trend of extreme climate indices indicated that the temperature was rising, the warming was significant, and the precipitation was increasing. During 1980–2020, the glacier mass balance was substantially correlated with the extreme temperature indices (TX90p, TXx) but not with the extreme precipitation indices. Analyzing on a seasonal scale, the summer mass balance was memorably correlated with the extreme temperature indices (TX90p, TX10p, TXx), and the correlation coefficient between winter mass balance and the extreme precipitation index R95p and winter precipitation was in the range 0.36~0.40 (p < 0.05). According to the correlation between glacier mass balance and extreme climate indices, the summer mass balance was mainly affected by temperature, and the winter mass balance was affected primarily by precipitation.

Raindrop size distribution characteristics in summer of a nival glacial zone in eastern Tianshan, Central Asia

Precipitation is a key component of the hydrological cycle, which is critical to understanding its formation and evolution. In this study, based on the observation data of the PWS100 located at the meteorological observation site at the terminal of Urumqi Glacier No. 1, eastern Tianshan Mountains, the statistical characteristics of the summer raindrop size distribution (DSD) were analyzed, and the DSD characteristics of five different rainfall rates(R) and two rainfall types (convective and stratiform) were investigated for the daytime and nighttime. The average raindrop spectral width was the largest in class III (1 < R < 5 mm h−1). The result showed that the raindrop concentration increased with the rainfall rate. The maximum raindrop concentration was at class IV (5 < R < 10 mm h−1), when the raindrop diameter was higher than 1.74 mm. The small and medium size raindrops played a dominant role in precipitation composition in the head watershed of the Urumqi River, contributing 98% of the total raindrop. The convective precipitation at the headwaters was divided into continental clusters. The stratiform/convective Dm-log10Nw was characterized by a large mass-weighted mean diameter Dm = 1.523/2.608, and a generalized intercept log10Nw = 2.841/3.469. N(D) of convective precipitation was significantly different between the daytime and nighttime, while that of stratiform precipitation was almost the same. The constraint relationship between R-Dm and R-log10Nw of these two precipitation types was deduced, the exponent of the R-log10Nw relationship of the two precipitation types was negative, and the Dm value of stratiform precipitation tended to be stable at a higher rainfall rate (1–2 mm). Finally, we deduced the power-law relationship between radar reflectivity (Z) and rain rate (R) [Z = A*Rb] for stratiform and convective precipitation at the headwaters. Z = 698.8R2.0 was for stratiform, and Z = 47.1R2.0 was for convective. These results, for the first time, offer insights into the microphysical nature of precipitation in the head watershed of the Urumqi River during the summer and provide essential information that could be useful for precipitation retrievals based on weather radar observations.

Changes in the Runoff of Urumqi Glacier No. 1 Under Climate Change: From Historical Observation to Future Prediction

This study explores the ice volumes of Urumqi Glacier No. 1 from 2013 to 2112 to examine the changes in the runoff of the glacier. Based on the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the changes of the glacier were predicted under three hypothetical climate scenarios: SSP1-1.9, SSP2-4.5, and SSP5-8.5 scenarios. The results derived from the Elmer/Ice ice-flow model showed increasing runoff till 2040 in the SSP2-4.5 and SSP5-8.5 scenarios and gradually decreasing runoff in the SSP1-1.9 scenario. The glacier areas and ice volumes of the two branches will keep declining under all the climate scenarios, including fast reductions until 2080 and slow reductions by the end of the ablation period. Moreover, the east branch (EB) will disappear at the end of the 21st century under the SSP2-4.5 and SSP5-8.5 scenarios. With much mass loss of the EB under all the climate scenarios, the runoff will increase in the early 100-year period and decrease until it is being infinitely close to the precipitation, which is similar with that of the west branch (WB). Since 2070, the ice volumes of the WB will contribute more than 50% of the whole glacier volumes under all the climate scenarios. The WB ice volume percentage will reach 100% in 2080 for the disappearance of the EB under the SSP5-8.5 scenario. As the fast retreat of the EB before 2080, the variations of the total runoff will be consistent with that of the EB runoff, and the EB runoff will account for more than 60% of the total runoff before 2070 under all the climate scenarios. Even if the meltwater of Urumqi Glacier No. 1 is stable from the late 21st century (after 2090), it will decline to approximately 15% of that in 2013. It will greatly influence the runoff of Urumqi River, hence human life and biodiversity.

Effect of topography on the changes of Urumqi Glacier No. 1 in the Chinese Tianshan Mountains

Topography plays an important role in determining the glacier changes. However, topography has often been oversimplified in the studies of the glacier changes. No systematic studies have been conducted to evaluate the relationship between the glacier changes and topographic features. The present study provided a detailed insight into the changes in the two branches (east branch and west branch) of Urumqi Glacier No. 1 in the Chinese Tianshan Mountains since 1993 and systematically discussed the effect of topography on the glacier parameters. This study analyzed comprehensive recently observed data (from 1992/1993 to 2018/2019), including mass balance, ice thickness, surface elevation, ice velocity, terminus, and area, and then determined the differences in the changes of the two branches and explored the effect of topography on the glacier changes. We also applied a topographic solar radiation model to analyze the influence of topography on the incoming shortwave radiation (SWin) across the entire glacier, focusing on the difference in the SWin between the two branches. The glacier mass balance of the east branch was more negative than that of the west branch from 1992/1993 to 2018/2019, and this was mainly attributed to the lower average altitude of the east branch. Compared with the west branch, the decrease rate of the ice velocity was lower in the east branch owing to its relatively increased slope. The narrow shape of the west branch and its southeast aspect in the earlier period resulted in a larger glacier terminus retreat of the west branch. The spatial variability of the SWin across the glacier surface became much larger as altitude increased. The SWin received by the east branch was slightly larger than that received by the west branch, and the northern aspect could receive more SWin, leading to glacier melting. In the future, the difference of the glacier changes between the two branches will continue to exist due to their topographic differences. This work is fundamental to understanding how topographic features affect the glacier changes, and provides information for building different types of relationship between the glacier area and ice volume to promote further studies on the basin-scale glacier classification.

Quantifying the Artificial Reduction of Glacial Ice Melt in a Mountain Glacier (Urumqi Glacier No. 1, Tien Shan, China)

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.

Urban air quality in Xinjiang and snow chemistry of Urumqi Glacier No. 1 during COVID-19's restrictions.

The unprecedented COVID-19 outbreak impacted the world in many aspects. Air pollutants were largely reduced in cities worldwide in 2020. Using samples from two snow pits dug separately in 2019 and 2020 in Urumqi Glacier No. 1 (UG1) in the Xinjiang Uygur Autonomous Region (Xinjiang), China, we measured water-stable isotopes, soluble ions, and black and organic carbon (BC and OC). Both carbon types show no significant variations in the snow-pit profiles dated from 2018 through 2020. The deposition of anthropogenically induced soluble ions (K+, Cl−, SO42−, and NO3−) in the snow decreased to 20–40% of their respective concentrations between 2019 and 2020; however, they increased 2- to fourfold from 2018 to 2019. We studied the daily concentrations of SO2 (2019–2020), NO2 (2015–2020), CO (2019–2020), and PM2.5 (2019–2020) measured in the sixteen major cities and towns across Xinjiang. The variabilities in these air pollutants were supposed to illustrate the air quality in the urban area and represent the change in the source area. The NO2 decreased in response to mobility restrictions imposed by local governments, while SO2, CO, and PM2.5 did not consistently correspond. This difference indicates that the restriction measures primarily affected traffic. The increases in chemical species in the snow from 2018 to 2019 and the subsequent decreases from 2019 to 2020 were consistent with the variations in SO2 and NO2 measured in urban air and estimated by MERRA-2 model. Therefore, the pandemic could possibly have an impact on snow chemistry of the Tien-Shan glaciers via reduced traffic and industrial intensity; more evidence would be obtained from ice cores, tree rings, and other archives in the future.

Three-Dimensional Flow Velocity Estimation of Mountain Glacier Based on SAR Interferometry and Offset-Tracking Technology: A Case of the Urumqi Glacier No.1

Remote sensing estimations of glacier flow velocity could provide effective methods for the long-term monitoring of glacier flow velocity. This paper calculated the velocity in the line-of-sight (LOS) direction by combining DInSAR and offset-tracking technology with ascending and descending Sentinel-1 images of the Urumqi Glacier No.1 from 2016 to 2017. Meanwhile, the velocity in the azimuthal direction was obtained by combining MAI and offset-tracking technology. Then, the eastward, northward, and upward flow velocities were retrieved using the Helmert variance component estimation method. Finally, the standard error of the mean and mean errors of surface velocity in non-glaciated areas of the Urumqi Glacier No.1 were calculated to evaluate the accuracy of the results generated by the proposed method. The results showed: (1) The ascending LOS velocity and the descending LOS velocity were 1.812 m/a and −1.558 m/a from 2016 to 2017. The ascending azimuthal and descending azimuthal velocities were 0.978 m/a and −2.542 m/a, respectively. (2) The glacier flow velocities were 2.571 m/a and 1.801 m/a, respectively, for the eastward and northward directions. In the vertical direction, the velocity was −0.554 m/a. (3) The accuracy of the results generated by the proposed method were 0.028 m/a, 0.085 m/a, and 0.063 m/a in the east, north, and vertical directions. Therefore, it is suitable to use ascending and descending Sentinel-1 images and the study method proposed in this paper to estimate the surface flow velocity of mountain glaciers.

Anomaly of glacier mass balance in different vertical zones and responses to climate modes: Urumqi Glacier No. 1, China

Anomaly of glacier mass balance in different vertical zones and responses to climate modes: Urumqi Glacier No. 1, China