Insights into permafrost aggradation and thawing: A case study of Zonag Lake on the Qinghai–Tibet Plateau using SAR interferometry

Lakes on the Qinghai–Tibet Plateau (QTP) are important indicators of climate change. The water level and area of Zonag Lake have increased sharply since 2000, and the west lake bottom area was exposed after an outburst of flood in September 2011. The drained basin was exposed to the cold environment, causing rapid permafrost forming. In this paper, time-series synthetic aperture radar interferometry (InSAR) was utilized to monitor the surface deformation of the drained basin using Sentinel-1A images within a 4-year period (2017–2020). This research focused on characterizing the spatial and temporal dynamics of ground deformation and exploring changes in the permafrost base around the drained basin based on the deformation information. The experimental results revealed spatially variable ground deformation, with long-term deformation rates ranging from −78.3 mm/year to 72.8 mm/year and seasonal amplitudes of 0–14 mm. Subsidence was prominent in the lakeshore, the thermokarst region and the slope drainage area, indicative of the thawing of ice-rich permafrost. Conversely, uplift was concentrated in the exposed unconsolidated sediment region, with a maximum displacement of 110 mm over the nearly 4-year observation period, suggesting ground ice aggradation. The uplift information was used to estimate the change in the permafrost base in the drained basin, yielding a maximum value of 4 m. The estimated permafrost base change closely aligned with simulated results, with an error of 0.28 m. This study demonstrates the capability of InSAR in monitoring permafrost stability and improving the understanding of the dynamic permafrost formation process.