Monitoring glacier flow is vital to understand the response of mountain glaciers to environmental forcing in the context of global climate change. Seasonal and interannual variability of surface velocity in the temperate glaciers of the Parlung Zangbo Basin (PZB) has attracted significant attention. Detailed patterns in glacier surface velocity and its seasonal variability in the PZB are still uncertain, however. We utilized Landsat-8 (L8) OLI data to investigate in detail the variability of glacier velocity in the PZB by applying the normalized image cross-correlation method. On the basis of satellite images acquired from 2013 to 2020, we present a map of time-averaged glacier surface velocity and examined four typical glaciers (Yanong, Parlung No.4, Xueyougu, and Azha) in the PZB. Next, we explored the driving factors of surface velocity and of its variability. The results show that the glacier centerline velocity increased slightly in 2017–2020. The analysis of meteorological data at two weather stations on the outskirts of the glacier area provided some indications of increased precipitation during winter-spring. Such increase likely had an impact on ice mass accumulation in the up-stream portion of the glacier. The accumulated ice mass could have caused seasonal velocity changes in response to mass imbalance during 2017–2020. Besides, there was a clear winter-spring speedup of 40% in the upper glacier region, while a summer speedup occurred at the glacier tongue. The seasonal and interannual velocity variability was captured by the transverse velocity profiles in the four selected glaciers. The observed spatial pattern and seasonal variability in glacier surface velocity suggests that the winter-spring snow might be a driver of glacier flow in the central and upper portions of glaciers. Furthermore, the variations in glacier surface velocity are likely related to topographic setting and basal slip caused by the percolation of rainfall. The findings on glacier velocity suggest that the transfer of winter-spring accumulated ice triggered by mass conservation seems to be the main driver of changes in glacier velocity. The reasons that influence the seasonal surface velocity change need further investigation.

Mountain glaciers are excellent indicators of climate change and have an important role in the terrestrial water cycle and food security in many parts of the world. Glaciers are the major water source of rivers and lakes in the Nyainqentanglha Mountains (NM) region, where the glacier area has the second largest extent on the Tibetan Plateau. The potential of the high spatial resolution ZiYuan-3 (ZY-3) Three-Line-Array (TLA) stereo images to retrieve glacier mass balance has not been sufficiently explored. In this study, we optimized the procedure to extract a Digital Elevation Model (DEM) from ZY-3 TLA stereo images and estimated the geodetic mass balance of representative glaciers in the two typical areas of the NM using ZY-3 DEMs and the C-band Shuttle Radar Topography Mission (SRTM) DEM in three periods, i.e., 2000-2013, 2013-2017 and 2000-2017. The results provide detailed information towards better understanding of glacier change and specifically show that: (1) with our new stereo procedure, ZY-3 TLA data can significantly increase point cloud density and decrease invalid data on the glacier surface map to generate a high resolution (5 m) glacier mass balance map; (2) the glacier mass balance in both the Western Nyainqentanglha Mountains (WNM) and Eastern Nyainqentanglha Mountains (ENM) was negative in 2000-2017, and experienced faster mass loss in recent years (2013-2017) in the WNM. Overall, the glaciers in the western and eastern NM show different change patterns since they are influenced by different climate regimes; the glacier mass balances in WNM was-0.22 ± 0.23 m w.e. a^-1 and-0.43 ± 0.06 m w.e. a^-1 in 2000-2013 and 2013-2017, respectively, while in 2000-2017, it was-0.30 ± 0.19 m w.e. a^-1 in the WNM and-0.56 ± 0.20 m w.e. a^-1 in the ENM; (3) in the WNM, the glaciers experienced mass loss in 2000-2013 and 2013-2017 in the ablation zone, while in the accumulation zone mass increased in 2000-2013 and a large mass loss occurred in 2013-2017; as regards the ENM, the glacier mass balance was negative in 2000-2017 in both zones; (4) glacier mass balance can be affected by the fractional abundance of debris and glacier slope; (5) the glacier mass balances retrieved by ZY-3 and TanDEM-X data agreed well in the ablation zone, while a large difference occurred in the accumulation zone because of the snow/firn penetration of the X-band SAR signal.

Mountain glaciers are one of the major fresh water resources. Glacier mass balance on the Tibetan Plateau (TP) can directly reflect local climate change and plays a crucial role in the terrestrial water cycle and food security of local people. In this study, we improved the procedure to analyze Three-Line-Array (TLA) stereo images to estimate the glaciers mass balance in Kangri Karpo mountains using Zi Yuan-3 (ZY-3) TLA data and C-band Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) in two periods, i.e. 2000-2013 and 2013-2017. The results showed that the mean mass balance of glaciers between 2000 and 2017 was -0.91 ± 0.02 m w.e. a^-1. The glaciers presented accelerated mass loss in recent years (2013-2017, -2.84 ±0.05 m w.e. a^-1), compared with the first decade in 21st (2000-2013, -1.59 ± 0.03 m w.e. a^-1), while the melt rate in debris-covered glaciers was larger than in clean-ice glaciers.

Mountain glaciers are sensitive to climate change and are thus relevant indicators of regional climate variability. In order to understand the dynamics of glaciers, retrieving glacier surface velocity is valuable in understanding physical processes in glaciers. We apply an image cross-correlation algorithm in the frequency domain to derive glacier velocity on the Yanong glacier between 2013 and 2018. The results indicate that the flow patterns are related to the terrain complexity. Yanong Glacier maximum velocity was 168 m/year at the elevation around 4700 meters. The surface velocity exceeded 100 m/year above the elevation of 4200 m, while above 5000 m the surface velocity fluctuated around 60 m/year along the main stream.