Estimating the lake storage capacity on the Tibetan Plateau using satellite altimetry and imagery data: a comparative analysis of water volume change methods

Compared to lake area and water level, lake storage capacity more intuitively reflects regional climate changes. In this study, we first derived lakebed elevation profiles for individual ICESat-2 tracks based on the underwater stratification of laser photons, then integrating all valid elevation tracks within the water body to interpolate the bathymetry. On this basis, we calculated the capacity and its time series directly, with the aid of lake boundaries and water levels obtained from optical imagery and CryoSat-2 data. Next, we also applied an empirical formula to estimate the water volume changes of Bangdag Co by combining the area and water levels from 2010 to 2023. Finally, we compared the results of Bangdag Co's water volume changes obtained from the two different methods and conducted a detailed analysis of their performance and regional applicability. The bathymetric map of Bangdag Co reveals a distinct spatial pattern, with the northeastern part significantly deeper (with a maximum depth of 35.27 m) and the southwestern part shallower. The average depth of the lake is 13.99 m. We further estimated that the lake storage capacity in November 2023 was 2.95 km³. Water volume changes estimated using the empirical formula were highly consistent with those derived from the lake storage capacity time series (from 2010 to 2023, the lake storage capacity increased by 1.04 km³). Our comparison revealed that the empirical formula method reflects only changes in water volume. In contrast, while our method can accurately estimate lake storage capacity, it is constrained to shallow, clear, and elongated east-west lakes (e.g., Ayakkum Lake). In summary, the ICESat-2 laser altimetry data, which do not rely on measured water depths, offer an essential complement to underwater topography detection and provide a novel perspective on lake volume estimation research.