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The direct glaciological method provides in situ observations of annual or seasonal surface mass balance, but can only be implemented through a succession of intensive in situ measurements of field networks of stakes and snow pits. This has contributed to glacier surface mass-balance measurements being sparse and often discontinuous in the Tien Shan. Nevertheless, long-term glacier mass-balance measurements are the basis for understanding climate–glacier interactions and projecting future water availability for glacierized catchments in the Tien Shan. Riegl VZ®-6000 long-range terrestrial laser scanner (TLS), typically using class 3B laser beams, is exceptionally well suited for repeated glacier mapping, and thus determination of annual and seasonal geodetic mass balance. This paper introduces the applied TLS for monitoring summer and annual surface elevation and geodetic mass changes of Urumqi Glacier No. 1 as well as delineating accurate glacier boundaries for 2 consecutive mass-balance years (2015–2017), and discusses the potential of such technology in glaciological applications. Three-dimensional changes of ice and firn–snow bodies and the corresponding densities were considered for the volume-to-mass conversion. The glacier showed pronounced thinning and mass loss for the four investigated periods; glacier-wide geodetic mass balance in the mass-balance year 2015–2016 was slightly more negative than in 2016–2017. Statistical comparison shows that agreement between the glaciological and geodetic mass balances can be considered satisfactory, indicating that the TLS system yields accurate results and has the potential to monitor remote and inaccessible glacier areas where no glaciological measurements are available as the vertical velocity component of the glacier is negligible. For wide applications of the TLS in glaciology, we should use stable scan positions and in-situ-measured densities of snow–firn to establish volume-to-mass conversion. [ABSTRACT FROM AUTHOR]

We describe the use of a terrestrial laser scanner (TLS) to monitor the net mass balance of Urumqi Glacier No. 1, eastern Tien Shan. We used an ultra-long-range Riegl VZ®-6000 TLS, which is specially designed for surveying snow- and ice-covered terrain, to create repeated high spatiotemporal resolution DEMs, focusing on the monthly-scale (25 April–28 May 2015) net mass balance. According to the TLS-derived DEMs, the area of Urumqi Glacier No. 1 was 1.558 km2 on 25 April 2015 and the average surface elevation change was 0.225 m. By comparing the results from the use of TLS with the conventional glaciological mass-balance method, the correlation coefficient (R2) between glaciological elevation changes of individual stakes and the TLS-derived geodetic elevation change of corresponding points was 0.85. Considering the uncertainty of both methods, this is a promising result. Using the in situ measured snow densities (snow pits) of the glacier surface, the geodetic net mass balance was 0.074 m w.e., which is slightly positive. The mean uncertainty in the TLS-derived monthly net mass balance was 0.018 m w.e., showing that the TLS surveying system presented accurate and relevant results and is therefore suitable to monitor mass-balance evolution of mountain glaciers. [ABSTRACT FROM PUBLISHER]

Originating in the Tian Shan mountains, Urumqi River plays a key role in terms of water supply to downstream areas. In its headwaters, Urumqi Glacier No. 1 (UG1) is the largest glacier contributing to water discharge. Assessing its response to the changing climatic conditions in the area is of major importance to quantify future water availability. We here apply COSIPY, a COupled Snowpack and Ice surface energy and mass balance model in PYthon, to UG1, implementing a new albedo parameterization which integrates site-specific bare-ice albedo values on a pixel-by-pixel basis observed by remote sensing. We assess model performance threefold: quantitatively based on long-term measurement data of (1) surface mass balance (SMB) and (2) water discharge as well as qualitatively (3) comparing simulated snow line altitudes to such imated on the basis of time-lapse photography. Comparison of the modeled SMB with annually-averaged data from ablation stakes reveals that COSIPY including the new albedo parameterization accounts for 57.6% of the variance observed in the measurements. The original albedo parameterization performs only slightly inferior (57.1%). Glacier-wide comparison between modeled and glaciological SMB shows high agreement. In terms of discharge prediction, COSIPY reproduces onset and duration of the discharge season well. Estimated discharge from the whole catchment shows shortcomings in exactly matching the measured times series, but interannual variability is captured. [ABSTRACT FROM AUTHOR]

In this study, energy and mass balance is quantified using an energy balance model to represent the glacier melt of Urumqi Glacier No. 1, Chinese Tian Shan. Based on data from an Automatic Weather Station (4025 m a.s.l) and the mass balance field survey data nearby on the East Branch of the glacier, the "COupled Snowpack and Ice surface energy and Mass balance model" (COSIMA) was used to derive energy and mass balance simulations during the ablation season of 2018. Results show that the modeled cumulative mass balance (−0.67 ± 0.03 m w.e.) agrees well with the in-situ measurements (−0.64 ± 0.16 m w.e.) (r2 = 0.96) with the relative difference within 5% during the study period. The correlation coefficient between modeled and observed surface temperatures is 0.88 for daily means. The main source of melt energy at the glacier surface is net shortwave radiation (84%) and sensible heat flux (16%). The energy expenditures are from net longwave radiation (55%), heat flux for snow/ice melting (32%), latent heat flux of sublimation and evaporation (7%), and subsurface heat flux (6%). The sensitivity testing of mass balance shows that mass balance is more sensitive to temperature increase and precipitation decrease than temperature decrease and precipitation increase. [ABSTRACT FROM AUTHOR]

Energy exchanges between atmosphere and glacier surface control the net energy available for snow and ice melt. Based on the meteorological records in Urumqi River Glacier No.1 (URGN1) in the Chinese Tien Shan during the period of 2012–2015, an energy-mass balance model was run to assess the sensitivity of glacier mass balance to air temperature (T), precipitation (P), incoming shortwave radiation (Sin), relative humidity (RH), and wind speed (u) in the URGN1, respectively. The results showed that the glacier melting was mainly controlled by the net shortwave radiation. The glacier mass balance was very sensitivity to albedo for snow and the time scale determining how long the snow albedo approaches the albedo for firn after a snowfall. The net annual mass balance of URGN1 was decreased by 0.44 m w.e. when increased by 1 K in air temperature, while it was increased 0.30 m w.e. when decreased by 1 K. The net total mass balance increased by 0.55 m w.e. when increased precipitation by 10%, while it was decreased by 0.61 m w.e. when decreased precipitation by 10%. We also found that the change in glacier mass balance was non-linear when increased or decreased input condition of climate change. The sensitivity of mass balance to increase in Sin, u, and RH were at −0.015 m w.e.%−1, −0.020 m w.e.%−1, and −0.018 m w.e.%−1, respectively, while they were at 0.012 m w.e.%−1, 0.027 m w.e.%−1, and 0.017 m w.e.%−1 when decreasing in those conditions, respectively. In addition, the simulations of coupled perturbation for temperature and precipitation indicated that the precipitation needed to increase by 23% could justly compensate to the additional mass loss due to increase by 1 K in air temperature. We also found that the sensitivities of glacier mass balance in response to climate change were different in different mountain ranges, which were mainly resulted from the discrepancies in the ratio of snowfall to precipitation during the ablation season, the amount of melt energy during the ablation season, and precipitation seasonality in the different local regions. [ABSTRACT FROM AUTHOR]

Glaciers are not only direct proxy for climate change, but also important water resources for heavy population in Central Asia. In China, many large rivers head from glaciers in mountains. Among those mountains, Qilian Mountain and its surroundings is characterized by small glaciers developed, dense population and extremely dry climate. Glaciers and snow melt water are heavily depended on in that area. Prohibited by limited studies on regional scale glacier behavior and its mechanisms, the significance of glaciers in Qilian Mountain is of debate. In this study, remote sensing, mass balance model and dynamic model are applied to (1) reconstruct area and mass loss of glaciers in the past 50 years and (2) predict them in 21st century, as well as (3) calculate current and future contribution of glaciers to local river stream. The results indicate glaciers in Qilian Mountain are more sensitive to climate change comparing to those glaciers in Tianshan and other mountains in Tibetan Plateau. One of the main reasons for that is the smaller mean glacier size. Certain part of glaciers in Qilian Mountain are predicted to vanish in very near future with climate change scenarios published in IPCC AR5 as climate forcing. We also supply proof for significant contribution of glaciers to local river runoff, even with the coverage of glaciers in the whole mountain range and surroundings less than 5%. [ABSTRACT FROM AUTHOR]

Abstract: Glaciological and geodetic measurements are two methods to determine glacier mass balances. The mass balance of Urumqi Glacier No. 1 has been measured since 1959 by the glaciological method using ablation stakes and snow pits, except during the period 1967–1979 when the observations were interrupted. Moreover, topographic surveys have been carried out at various time intervals since the beginning of the glacier observations. Therefore, glacier volume changes are calculated by comparing topographic maps of different periods during nearly 50 years. Between 1962 and 2009, Urumqi Glacier No. 1 lost an ice volume of 29.51×106 m3, which corresponds to a cumulative ice thickness loss of 8.9m and a mean annual loss of 0.2m. The results are compared with glaciological mass balances over the same time intervals. The differences are 2.3%, 2.8%, 4.6%, 4.7% and 5.9% for the period 1981–1986, 1986–1994, 1994–2001, 2001–2006 and 2006–2009, respectively. For the mass balance measured with the glaciological method, the systematic errors accumulate linearly with time, whereas the errors are random for the geodetic mass balance. The geodetic balance is within the estimated error of the glaciological balance. In conclusion, the geodetic and glaciological mass balances are of high quality, and therefore, there is no need to calibrate the mass balance series of Urumqi Glacier No. 1. [Copyright &y& Elsevier]

Abstract The mass balance of Urumqi Glacier No.1, eastern Tien Shan, has been monitored since 1959, using the direct glaciological method. This study presents a detailed comparison of the glaciological mass balance with a high-quality product of geodetic surveys in the overlapping period from 1981 to 2015. We analyzed the generic differences between glaciological and geodetic mass-balance measurements, including in-depth uncertainties assessments. The statistical comparison shows that the reduced discrepancy (δ = 0.53) between the geodetic mass balance (−0.53 ± 0.14 m w.e. a−1) and corrected annul glaciological mass balances (−0.46 ± 0.14 m w.e. a−1) falls within the 95% confidence interval and reveals that no statistical significant bias between the two datasets is detectable over the period. Thanks to the good agreement, calibration of the glaciological to the geodetic data series is currently not required. The more negative geodetic mass balance is probably relevant to the glacier surface characteristics. The uncertainty of our results measured with geodetic method was close to the majority of similar studies, but bigger than those derived from multi-temporal high-quality DEMs. Further studies should continue using a long-range terrestrial laser scanning (TLS) system to derive high-resolution and -precision digital elevation models (DEMs) of the glacier surface at the monthly time-scale, which will provide a powerful complement to the glaciological measurements. Highlights • No statistical significant bias between the geodetic and glaciological mass balance of Urumqi Glacier No.1 is detectable. • A calibration of the glaciological data series is currently not required. • Further studies should continue using a long-range terrestrial laser scannner to monitor the glacier mass balance. [ABSTRACT FROM AUTHOR]

Glacier flow velocity of Urumqi Glacier No. 1 has been continuously measured at the end of every summer since 1980. The observation results show that the average surface velocity was 5.5 m a − 1 , 4.6 m a − 1 , 3.8 m a − 1 , and 3.3 m a − 1 in 1980/1981, 1990/1991, 2000/2001, and 2010/2011, respectively. The annual average velocity was reduced by 1.3% a − 1 from 1980/1981 to 2011/2012. The climate change is the essential cause for long term velocity change because continuous mass loss or gain will result in ice thickness decrease or increase. A suddenly sharp change in the mass balance could lead to a short change in velocity. Long term change in the velocity can be analyzed by glacial dynamic model. Using the simplified equations, analysis of the surface velocity along the centerline shows that influence of the ice thickness change is most important and could be modeled well. The velocity is very sensitive to the surface slope change but the validity of its effect modeling is relatively low due to the large spatial variability of surface slope. Under the combination effect of decrease in both ice thickness and surface slope, the velocity of the West Branch has a relative large decrease. The calculated decrease in surface velocity along the centerline is 3.8 m a − 1 from 1981 to 2012, relatively close to the value of 3.6 m a − 1 from observation. Increase in surface slope of the East Branch has an offsetting effect on ice thickness decrease. To further analysis, besides more data, a better model is needed to describe physical and dynamic processes. [ABSTRACT FROM AUTHOR]

The importance of glaciers for providing runoff is reflected in the extensive glacier measurement record for China. In this paper, we summarized the mass-balance and front-variation data of glaciers in China that have long-term records. Mass balance has been measured for 22 glaciers; length (or front-position) records exist for 96 glaciers. We found that the mean rate of glacial mass balance decreased by −0.015 m w.e. (water equivalent) per year during the period 1959–2015, which was lower than that for glaciers globally (−0.013 m w.e. per year). It was indicated that the rate of glacial melting (mass loss) increased in China, which was higher than that in glaciers worldwide. However, glacial frontal positions varied among mountains in time and space. Glaciers in the Karakoram Mountains mean advanced 379 m during the 1968–2000 period, while glaciers in the Pamir Mountains remained relatively stable from the 1960s through the 2000s, i.e., retreated 28 m. Glaciers in Hengduan Mountains retreated farthest (1250 m maximum) from 1930 to 2005. [ABSTRACT FROM AUTHOR]

Urumqi Glacier No. 1 in the Chinese Tien Shan has the longest measured mass balance record in China. It is located in Xinjiang province and forms the headwaters of Urumqi River. It is under constant monitoring since 1959 and therefore offers great potential for glacier mass balance modeling. Generally, glaciers in the Tien Shan, both in China and Kyrgyzstan, are strongly retreating. Since glacier meltwater is a considerable contribution to downstream freshwater supplies in surrounding lowlands, it is important to investigate possible future changes of melt water supply at high spatial and temporal resolution related to physical processes such as the atmospheric forcing, sublimation, refreezing, densification, etc. Here, we use the newly updated COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) in its 2-dimensional spatially distributed version to simulate energy and mass fluxes of Urumqi Glacier No. 1 since the year 2000. Available observational data include weather station data from a station close to the glacier, runoff data, and mass balance data based on ablation stakes and snow pits. COSIPY is forced by reanalysis data (ERA5), including air pressure, air temperature, cloud cover, relative humidity, solar radiation, solid or total precipitation, and wind speed at hourly resolution. ERA data is downscaled to the location of the glacier by statistical methods. The spatial pattern on the glacier is calculated subsequently based on a high-resolution digital elevation model. We present detailed spatial and temporal patterns of energy and mass fluxes and relate these to the observations in the study period. Future work will include model coupling with an ice dynamical model and coupling of the mass balance model with a subsequent hydrological model. [ABSTRACT FROM AUTHOR]