Nonlinear dynamics and threshold responses of Xing’an permafrost to climate and human disturbance in Northeast China: Insights from a multi-risk framework

The ecosystem-dominated Xing’an permafrost of Northeast China has degraded under rapid climate warming and intensifying human activities, threatening ecological security and infrastructure. Yet most assessments emphasize thermal states or geoenvironment−permafrost interactions, offering limited system-level appraisal. Here, we integrate multi-source datasets (19902020) to quantify landscape ecological risk (LER; disturbance and vulnerability components) and an entropy-weighted permafrost vulnerability index (PV), and combine them with equal weights into a comprehensive permafrost degradation risk metric (CPDR). CPDR effectively captures both temporal trajectory and spatial mosaic of degradation risk: Elevated CPDR consistently preceded major permafrost losses, demonstrating an early-warning capability, with high-risk zones concentrated in ecotones and human-disturbed corridors, while permafrost in mountainous forests remained comparatively stable. Thermal drivers, especially mean annual air temperature (MAAT) and mean annual minimum air temperature (MAMinAT), were the dominant accelerators, whereas vegetation cover (normalized difference vegetation index, NDVI) and snow cover (snow cover duration, SCD) generally mitigated risk. Threshold analysis revealed phase-dependent, nonlinear responses of the Xing’an permafrost to environmental forcing, with some critical thresholds (e.g., MAAT ≈ 0°C, NDVI ≈ 0.4 – 0.52, SCD ≈118 days), beyond which degradation risk rises sharply. PV provides the structural susceptibility, while LER modulates and amplifies local disturbances, and their coupling shapes CPDR. These findings highlight the need for integrated, threshold-aware risk management that links early warning to adaptive interventions and aligns permafrost protection with ecosystem-service co-benefits.