Spatiotemporal changes of frozen soil layers during 1960-2021 and future prediction in Northeast China

Frozen soil is highly sensitive to climate change. However, the characteristics and long-term changes of both seasonally frozen ground and permafrost are seldom known. The object of this study was to explore the temporal characteristics and causal factors of frozen soil in historic (1960−2021) and future (2021−2100) periods under different climate scenarios (SSP119, SSP245 and SSP585) in Northeast China using Mann-Kendall (MK) test, Sen's slope method, freeze-thaw indices, surface frost number model, extreme climate indicators and Geodetector method. In seasonally frozen ground regions, the maximum seasonal frozen depth reached approximately 2 m in spring (March−May). For permafrost regions, the southern boundary shifted northward at a rate of 4.44 km per year, resulting in decreased permafrost areas from 5.56×10 5 km 2 in the 1960s to 2.05×10 5 km 2 in the 2010s. Under future climate warming, permafrost degradation will be further accelerated, driven primarily by extreme temperature indices rather than precipitation. Additionally, cropland expansion and intensified human activity further accelerate the degradation of frozen soil. This study provides insights into the spatiotemporal dynamics of frozen soil in Northeast China, which may inform future efforts related to ecological protection and land management in cold regions.