Rapid thinning of lake ice for Himalayan glacial lakes since 2010

Abstract

Lake ice, a significant indicator of global warming, plays a crucial role in regulating regional hydroclimate and maintaining lake ecosystem balance, in particular for the fragile high-mountain environment in Asia. However, the spatiotemporal variability of ice thickness in glacial lakes remains elusive due to limited and inconsistent observations, as well as the lack of a comprehensive glacial lake ice model that effectively couples ice layer dynamics with multiple physical fields, such as atmosphere and lake water. Although efforts have been made in applying lake ice model based on climate model outputs, the estimation of lake ice thickness largely overlooks the actual frozen lake conditions and remains constrained to highly glaciated regions. Therefore, a systematical method for automatically extracting ice-covered area and estimating the ice thickness in glacial lakes is critically needed. Here we employed SDGSAT-1 MII images to meticulously delineate ice coverage regions, and harnessed CryoSat-2 waveforms to derive ice thickness in glacial lakes across Himalaya. Then we proposed a novel lake ice model that was cross-validated by altimetric measurements, with a Pearson correlation coefficient (CC) of 0.85 and RMSE of 0.25 m for the whole Himalaya, to give a reliable estimation of ice thickness for 64 Himalayan glacial lakes large than 1 km². The maximum mean ice thickness during 2010–2024 is 2.5 m, observed in Western Himalaya. Approximately 80 % of lakes are experiencing statistically significant reductions in ice thickness. The fastest decrease in lake ice thickness occurs in the Eastern Himalaya (up to 0.08 m/yr), and the thinning rates in the Western and Central Himalayas are comparatively lower, with the maximum values of 0.04 m/yr and 0.07 m/yr, respectively. Further investigations show that the associated lower ice is primarily driven by the notably rising temperature and accelerated glacier ablation. This research enhances the interpretations of SDGSAT-1 imagery signal from frozen glacial lakes, offering new possibilities for broader applications of SDGSAT-1 in cryospheric studies.