Contrasting feedback mechanisms drive basin-scale vegetation vulnerability to drought in cold-arid northern China

The cold-arid regions of northern China form a critical ecological security barrier, but face increasing drought risks in the context of global warming. Limited by static drought-vegetation response assumptions, prevailing approaches impede precise vulnerability assessment in these fragile ecosystems. Focusing on five representative basins in the regions, a basin-scale framework was established to assess vegetation vulnerability to drought based the Standardized Precipitation Evapotranspiration Index and a Composite Vegetation Index. The vegetation resistance, resilience, and vulnerability, and the critical thresholds for drought severity and duration, were systematically quantified. The severity and duration of vegetation-anomaly-inducing drought events gradually increased from 2.5 to 2.1 months in the eastern basin to 3.6 and 3.8 months in the west, respectively, while the peak intensity declined from 1.37 to 1.21.Within the range of growing-season events identified in this study, this indicates that vegetation anomalies in the eastern meadow and typical steppe basins tend to be associated with relatively shorter-duration but more intense drought events, whereas in the western desert and desert-steppe basins they are more often associated with relatively longer-duration drought events of moderate peak intensity. From the eastern Hailar River Basin to the central Heihe River Basin and further to the western Tarim River Basin, both vegetation resistance and resilience exhibited a decreasing-then-increasing trend, resulting in a corresponding rise and subsequent decline in vulnerability (from 0.36 to 0.66 and then to 0.37). Consistently, drought severity and duration thresholds were generally higher in the eastern basin (0.89 and 0.68 months, respectively) but lower in the western basin (0.61 and 0.57 months). This spatial differentiation stems from the dominance of contrasting threshold-dependent feedback mechanisms under meteorological drought. In the low-vulnerable eastern basin, a self-regulating negative feedback, hydrological improvements promoted vegetation recovery, which stabilized soil structure and further enhanced ecological resilience. Conversely, in high-vulnerability western basins, a self-reinforcing positive feedback prevails, where moisture depletion leads to vegetation degradation and soil deterioration, further reducing water availability and intensifying drought stress.