Changes in near-surface permafrost temperature and active layer thickness in Northeast China in 1961–2020 based on GIPL model

Characteristics of active layer processes depend on the conditions of the ground surface, coupled water-heat balance, soil hydrology, and soil properties under frozen and thawed states at shallow depths. Mean annual temperature at the bottom of the active layer (MATBAL) and active layer thickness (ALT) are important metrics in studying the features of active layer processes and the thermal stability of permafrost. Affected by the changing climate, permafrost regions in Northeast China have undergone remarkable changes in the past 30 years, many of which are still ongoing. In Northeast China, however, model studies on examining hydrothermal dynamics and on changes in frozen ground have faced serious challenges, including a complex ecological environment and rugged terrains. In this study, the Geophysical Institute Permafrost Lab (GIPL) model was used to map temporal and spatial variations in MATBAL and ALT in Northeast China, where discontinuous, island, and sporadic permafrost coexists with seasonal frost. Using the parameters of ground surface temperature (GST) and soil properties as input, we applied the GIPL model to analyze the distributive characteristics of near-surface permafrost in Northeast China. The results indicate a sharply shrinking permafrost area from 5.49 × 105 to 2.29 × 105 km2 but rapidly rising rates of 0.17–0.83 °C/decade in MATBAL in Northeast China during the period from 1961 to 2020. Under a persistently warming climate, accelerating permafrost degradation will inevitably affect the hydrological environment, boreal ecosystem, soil biology, and engineering infrastructure. This work fills a gap in the distribution of MATBAL and ALT in Northeast China.