Glacier mass change and evolution of Petrov Lake in the Ak-Shyirak massif, central Tien Shan, from 1973 to 2023 using multisource satellite data

Warming in the Third Pole region accelerates glacier and snow melt, leading to a rise in glacial lake numbers and sizes. However, accurately measuring their water level changes poses challenges, hindering precise volume assessments and evaluation of glacier mass balance contributions. Here, we took the Ak-Shyirak glaciers and the largest Petrov proglacial lake in the Central Tien Shan as a case study to investigate these phenomena. Specifically, firstly, we conducted mass balance assessments for the Ak-Shyirak massif for six sub-periods from 1973 to 2023 using KH-9 DEMs, SRTM DEM, and ASTER DEMs. The results indicate that glaciers were in a state of rapid melting for 1980–2000 and 2005–2012, with rates of −0.46 m w.e./a and − 0.37 m w.e./a; moderate melting during 1973–1980 and 2012–2018, with rates of −0.26 m w.e./a and − 0.28 m w.e./a, while slower melting during 2000–2005 and 2018–2023, with rates of −0.08 m w.e./a and − 0.18 m w.e./a. Subsequently, we conducted assessments of the area change of Petrov Lake for 1973–2023 using KH-9 and Landsat images. The results reveal a significant increase in the glacial lake area by 2.81 km² (150.25 %), corresponding to a rate of 0.054 km²/a over the entire study period. Furthermore, we conducted monitoring of Petrov Lake's water level from 2019 to 2023 by utilizing ICESat-2 laser altimetry and Sentinel-3 radar altimetry data. Our findings indicate that the glacial lake level shows intra-annual fluctuations and inter-annual change, with amplitudes of 0.67 ± 0.09 m and increase rate of 0.30 ± 0.05 m/a, respectively, as determined by a periodic fluctuation model. Finally, after a comprehensive analysis of ERA5-Land meteorological data, topography, glacier mass balance, lake area, and water level, we can draw the following conclusions: (1) glacier mass balance is predominantly influenced by the air temperature and snowfall; (2) changes in glacial lake area are driven by factors such as the lake basin, glacier surface elevation, and drainage event; (3) intra-annual fluctuations and inter-annual change in glacial lake levels are both primarily influenced by precipitation and glacier mass balance; (4) glacier mass balance accounts for (36.19 ± 8.47)% of the water supply contributing to changes in glacial lake volume change, while precipitation represents (63.81 ± 5.08)%. Glacier mass balance measurements reveal changing patterns in the Ak-Shyirak massif, Central Tien Shan, due to climate change. Inaugural proglacial lake level measurements provide unique insights into both intra-annual and inter-annual changes, serving as a reference for Third Pole region-wide glacial lake monitoring. Additionally, quantifying glacier meltwater contributions to lake volumes will aid future glacial lake evaluation and potential outburst flood impacts.