Ground surface temperature variations and their links to permafrost distribution in the Genhe River Basin, Da Xing'anling Mountain Range

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Ground surface temperature (GST) fundamentally controls permafrost distribution in transitional zones, yet the link between GST variability and permafrost occurrence remains poorly understood, particularly in Northeast China where systematic field evidence is scarce. We selected the Genhe River Basin, a southern boundary of high-latitude permafrost regions in the Da Xing’anling Mountain Range as the study area. We used GST observations from 69 sites across diverse vegetation and terrain settings and analyzed spatial variability to determine thermal thresholds for permafrost occurrence. Four GST variables—mean annual GST (MAGST), GST amplitude (AAGST), thawing degree days (TDD), and freezing degree days (FDD)—exhibited strong spatial heterogeneity. Geographic gradients explained only part of this variation, whereas vegetation types exerted a stronger influence. Across the basin, MAGST ranged from −3.6 to 4.3 °C (mean 1.0 °C) and frost number (FN) averaged 0.47. Importantly, permafrost occurrence was concentrated in larch forests, wetlands, and shrublands, corresponding to MAGST thresholds of 0.4–0.7 °C and FN values of 0.48–0.49. Analysis of MAGST lapse rate suggested that continuous permafrost might exist at higher elevations, with lower limits around 800 m on north-facing and 980 m on south-facing slopes. These results refine regional thermal thresholds and reveal the role of vegetation and slope aspect in sustaining permafrost under relatively warm conditions. They also provide new empirical evidence to support refined mapping and model calibration in transitional permafrost zones.