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Similar to most mountain glaciers in the world, Urumqi Glacier No. 1 (UG1), the best observed glacier in China with continued glaciological and climatological monitoring records of longer than 50 years has experienced an accelerated recession during the past several decades. The purpose of this study is to investigate the acceleration of recession. By taking UG1 as an example, we analyze the generic mechanisms of acceleration of shrinkage of continental mountain glaciers. The results indicate that the acceleration of mass loss of UG1 commenced first in 1985 and second in 1996 and that the latter was more vigorous. The air temperature rises during melting season, the ice temperature augment of the glacier and the albedo reduction on the glacier surface are considered responsible for the accelerated recession. In addition, the simulations of the accelerated shrinkage of UG1 are introduced in this article. [ABSTRACT FROM AUTHOR]

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]

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]

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]