Glacial changes are crucial to regional water resources and ecosystems in the Sawir Mountains. However, glacial changes, including the mass balance and glacial meltwater of the Sawir Mountains, have sparsely been reported. Three model calibration strategies were constructed including a regression model based on albedo and in-situ mass balance of Muz Taw Glacier (A-Ms), regression model based on albedo and geodetic mass balance of valley, cirque, and hanging glaciers (A-Mr), and degree-day model (DDM) to obtain a reliable glacier mass balance in the Sawir Mountains and provide the latest understanding in the contribution of glacial meltwater runoff to regional water resources. The results indicated that the glacial albedo reduction was significant from 2000 to 2020 for the entire Sawir Mountains, with a rate of 0.015 (10a)- 1, and the spatial pattern was higher in the east compared to the west. Second, the three strategies all indicated that the glacier mass balance has been continuously negative during the past 20 periods, and the average annual glacier mass balance was -1.01 m w.e. Third, the average annual glacial meltwater runoff in the Sawir Mountains from 2000 to 2020 was 22 x 106 m3, and its

Accurate estimates of regional and global glacier mass require many field-based sample measurements that are widely distributed across an area of interest. The Sawir Mountains are an isolated mountain system in Central Asia and changes in glacier mass balance from this region have rarely been reported. In this study, we provide a comprehensive analysis of mass changes of the Muz Taw Glacier in the Sawir Mountains based on glaciological and geodetic measurements. The glaciological mass balance exhibited a strong variability during the period 2016-2020, with a range of values between - 1.29 and - 0.31 m water equivalent (w.e.) and a mean value of - 0.86 +/- 0.16 m w.e. Differences in the surface elevation of the Muz Taw Glacier were determined from analysis of a topographic map (1:100,000 scale) and terrestrial laser scanning (TLS) point-cloud data, with these data sources indicating an average surface elevation change of approximately - 33.36 +/- 9.39 m or - 0.54 +/- 0.15 m a(-1) during 1959-2021. This thickness is roughly equivalent to half of the mean thickness of the glacier terminus, which has contributed to the negative geodetic mass balance of - 28.36 +/- 8.23 m w.e. or - 0.46 +/- 0.13 m w.e. a(-1). Approximately twice as much mass has been lost from the Muz Taw Glacier during the past 5 years (2016-2020) than estimated by geodetic data, indicating that the mass loss of Muz Taw Glacier has continued unabated.

The glaciers in the Sawir Mountains are an important freshwater resource, and glaciers have been experiencing a continuing retreat over the past few decades. However, studies on detailed glacier mass changes are currently sparse. Here, we present the high-precision evolution of annual surface elevation and geodetic mass changes in the ablation area of the Muz Taw Glacier (Sawir Mountains, China) over the latest three consecutive mass-balance years (2017-2020) based on multi-temporal terrestrial geodetic surveys. Our results revealed clearly surface lowering and negative geodetic mass changes, and the spatial changing patterns were generally similar for the three periods with the most negative surface lowering (approximately -5.0 to -4.0 m a(-1)) around the glacier terminus. The gradient of altitudinal elevation changes was commonly steep at the low elevations and gentle in the upper-elevation parts, and reduced surface lowering was observed at the glacier terminus. Resulting emergence velocities ranged from 0.11 to 0.86 m a(-1) with pronounced spatial variability, which was mainly controlled by surface slope, ice thickness, and the movement of tributary glaciers. Meanwhile, emergence velocities slightly compensated the surface ablation at the ablation area with a proportion of 14.9%, and dynamic thickening had small contributions to glacier surface evolution. Limited annual precipitation and glacier accumulation may result in these weak contributions. Higher-resolution surveys at the seasonal and monthly scales are required to get insight into the mass balance processes and their mechanism.