As one of the best indicators of the periglacial environment, ice-wedge polygons (IWPs) are important for arctic landscapes, hydrology, engineering, and ecosystems. Thus, a better understanding of the spatiotemporal dynamics and evolution of IWPs is key to evaluating the hydrothermal state and carbon budgets of the arctic permafrost environment. In this paper, the dynamics of ground surface deformation (GSD) in IWP zones (2018-2019) and their influencing factors over the last 20 years in Saskylakh, northwestern Yakutia, Russia were investigated using the Interferometric Synthetic Aperture Radar (InSAR) and Google Earth Engine (GEE). The results show an annual ground surface deformation rate (AGSDR) in Saskylakh at -49.73 to 45.97 mm/a during the period from 1 June 2018 to 3 May 2019. All the selected GSD regions indicate that the relationship between GSD and land surface temperature (LST) is positive (upheaving) for regions with larger AGSDR, and negative (subsidence) for regions with lower AGSDR. The most drastic deformation was observed at the Aeroport regions with GSDs rates of -37.06 mm/a at tower and 35.45 mm/a at runway. The GSDs are negatively correlated with the LST of most low-centered polygons (LCPs) and high-centered polygons (HCPs). Specifically, the higher the vegetation cover, the higher the LST and the thicker the active layer. An evident permafrost degradation has been observed in Saskylakh as reflected in higher ground temperatures, lusher vegetation, greater active layer thickness, and fluctuant numbers and areal extents of thermokarst lakes and ponds.

Lakes and permafrost on Qinghai-Tibet Plateau (QTP) are both important indicators of climate change. Previous literatures have shown the usefulness of optical remote sensing in lake expansion monitoring and the effectiveness of synthetic aperture radar (SAR) interferometry (InSAR) in retrieving permafrost deformation on QTP. However, none of them incorporated both optical remote sensing and InSAR to investigate an event that may exhibit causal links between lake outburst and permafrost degradation. This study integrated both the Google Earth Engine (GEE) analysis on optical images and the small baseline subset (SBAS) processing on SAR datasets to evaluate the potential impact of a lake outburst event on permafrost degradation. The outburst of Zonag Lake (headwater lake) that occurred on 14 September 2011 was focused, and its consequential influence on the permafrost degradation surrounding Salt Lake (tailwater lake) was investigated. The GEE processing on Landsat and HJ-1 imageries allowed an efficient monitoring of the Salt Lake expansion over past 20 years. In addition, the SBAS-InSAR analysis on temporal Envisat and Sentinel-1 datasets further discovered the accelerated permafrost degradation surrounding Salt Lake after 2014. The results provide an evidence that on QTP the outburst of a headwater lake may significantly accelerate the permafrost degradation surrounding the tailwater lake. Such degradation may be attributed to the thermal alteration of the permafrost thawing-freezing cycle and the melting ground ice, along with the subsequent changes on hydrological connectivity and soil permeability. With the continuous trend of the permafrost degradation surrounding Salt Lake, potential risks may be further exposed to the regional environment and infrastructures such as the Qinghai-Tibet railway and highway, thus deserving a particular attention in the near future. The novelties of this study are: 1) technically, the preliminary attempt to integrate the GEE and InSAR techniques for a joint analysis of lake expansion and permafrost degradation, and 2) scientifically, the finding that lake outburst may accelerate permafrost degradation on QTP.