Investigating the first case of permafrost degraded subsidence in Lahaul & Spiti region of Tethyan Himalayas.

Rising temperatures and changing precipitation patterns are causing rapid changes in the Himalayan ecosystem. Changes in climatic conditions affect various aspects of high mountain environments, including glaciers, rock glaciers, and permafrost, and pose significant threats to indigenous mountain communities. This study investigates the first case of permafrost thaw-induced subsidence in the Lindur Village of Lahaul & Spiti district of Himachal Pradesh using MT-InSAR method. We used 15 Sentinel-1 single-look complex images acquired from April 2022 to September 2022 along the ascending orbit track and used the SBAS technique to monitor the subsidence in the village. The results revealed significant land subsidence rates ranging from 7.9 to -6.8 cm/year. The cumulative land subsidence of 16 cm was observed over the northeast direction of the village. The analysis of historical temperature and precipitation data from 1950 to 2024 shows a significant rise in temperature at a rate of 0.02 °C/year and a shift in precipitation pattern over the village. From the field observations, the study found that the local geology and existing rock glaciers exacerbate the rate of subsidence leading to the development of cracks in the region. This is the first study that provides a detailed insight into the interaction of climatic, geological, and hydrological factors that drive permafrost thaw causing land subsidence in the Indian Tethyan Himalayas. The quantified deformation rates provide crucial information for developing targeted mitigation strategies and early warning systems.