Evidence of ground ice melting detected by InSAR and in situ monitoring over permafrost terrain on the Qinghai-Xizang (Tibet) Plateau

The thawing of ice-rich permafrost has attracted considerable attention in recent years. In this study, we analyzed both the ground surface deformation time series spanning 6 years, derived through the SBAS-InSAR technique on the Qinghai-Xizang (Tibet) Plateau (QTP), and the long-term active layer soil temperature and moisture in situ observations and their relationships. The results showed that long-term subsidence velocity directly represents the melting of ground ice instead of the thickening rate of the active layer by a quantitative analysis of both terrain subsidence velocity and active layer thickening rate and the increase in liquid water at the bottom of the active layer. Ice-poor permafrost thawing does not result in distinct subsidence, although the active layer deepening rate can be very high. The spatial analysis reveals that long-term deformation velocities are large in the foothills and on gentle slopes (1-5 degrees) and are closely related to geomorphological conditions, which could regulate the soil properties and ground ice content. These findings improve the understanding of the thawing degradation of icy permafrost and promote method developments for the automated mapping of ground ice melting in permafrost environments.