Permafrost thaw and thermokarst in the source region of the Yangtze river in the central Tibetan plateau revealed by radar and optical remote sensing

The landscape and landforms in permafrost regions are transforming due to climate change and permafrost thaw. This study uses optical and radar remote sensing, alongside spatial analysis, to examine thermokarst features and their driving factors in the source region of the Yangtze River (SRYR) on the central Tibetan Plateau. We analyse the distribution, interaction, and key environmental factors influencing thermokarst ponds and ground surface deformation, which are the two widespread and noticeable thermokarst features. Since the 1960s, the number of small water bodies has doubled from approximately ~2 × 10⁴ to ~4 × 10⁴ by the 2020s, with the median size of these water bodies decreasing from 2.3 × 10⁴ m² to 1.4 × 10⁴ m². The permafrost terrain has an average subsidence rate of 6.8 mm/a. About 50.9% of the SRYR exhibits evident thermokarst features. Surficial geological factors, especially geomorphology and slope, are primary factors in shaping the spatial distributions of thermokarst features. Both seasonal deformation and long-term subsidence rates are more pronounced in areas with thermokarst ponds. However, once pond coverage exceeds around 5%, the amplifying effect on long-term subsidence rates and seasonal deformation diminishes. The investigation further reveals that the relationship between seasonal deformation and long-term subsidence is not strictly linear and that the combined increase in seasonal deformation and long-term subsidence applies only to areas with seasonal deformation below approximately 20 mm. Beyond this threshold, the long-term subsidence rate is no longer exacerbated by increased seasonal deformation.