Long-term InSAR and streamflow recession analysis reveal accelerated permafrost degradation in the mining area of Qilian Mountain

Abstract. Permafrost underlies about 40 % of the Qinghai-Tibet Plateau (QTP), where climate warming and human activities increasingly threaten fragile alpine ecosystems, necessitating long-term permafrost monitoring. Interferometric Synthetic Aperture Radar (InSAR) enables precise detection of thaw-induced surface deformation, while streamflow recession helps reveal subsurface hydrological changes with permafrost degradation. This study performed a first-time joint analysis of decades-long InSAR surface deformation and streamflow recession to assess the trajectory of permafrost degradation in the source region of the Datong River, an area located in the Qilian Mountains of the northeastern QTP and subject to intensive mining during the 2000s and early 2010s. A data-constrained Small Baseline Subset (SBAS) method was proposed to improve the Sentinel-1 C-band deformation retrievals through integrating a linear–periodic temporal constraint model and using concurrent ALOS-2 retrieved deformation rate as a reference. A consistent long-term (1997–2023) deformation dataset was then generated through combining multi-sensor C- and L-band SAR retrievals. The results reveal minimal surface deformation before the mining, followed by sustained ground subsidence (−15 to −5 mm a⁻¹) and enhanced seasonal deformation (~20–60 mm) during and after mining, indicating accelerated permafrost degradation. This acceleration coincides with a marked slowdown in the post-mining streamflow recession rate derived from daily discharge data of the upper Datong River, likely driven by thaw-induced increases in basin subsurface water storage and flowpath connectivity. This study provides a first comprehensive assessment of permafrost degradation from both surface and subsurface perspectives, offering valuable insights for integrating remote sensing and hydrological observations to assess permafrost vulnerability.