Multidimensional aspects of drought event evolution drive the spatiotemporal heterogeneity of vegetation photosynthetic responses

• A three-dimensional clustering approach to identify drought events. • Coupling drought events with SIF enabled event-level assessment of vegetation photosynthetic sensitivity. • Vegetation photosynthesis exhibits heightened sensitivity under soil moisture deficits ≤ 30th percentile. Droughts exert profound impacts on the terrestrial carbon cycle, yet current understanding of vegetation carbon uptake remains largely constrained by the ways drought processes are characterized, particularly by the neglect of event-scale and process-level heterogeneity. In this study, we employed a three-dimensional clustering approach with daily soil moisture data (2000–2024) to identify 32 typical drought events across China, track their complete lifecycles, and link evolutionary characteristics to vegetation photosynthetic response thresholds. XGBoost model was further employed to disentangle the hierarchical influences of environmental drivers. Results show that summer constitutes the primary drought season nationwide, with events persisting significantly longer than those in other seasons. Droughts in the middle-lower Yangtze River Plain and Southwest China predominantly occurred in winter and spring, whereas those in the North China-Northeast Plain concentrated in early summer and frequently extended into late autumn. Regional dynamics varied markedly: North China-Northeast Plain droughts displayed longer migration pathways and faster propagation rates; Southwest China events were characterized by high intensity and prolonged stress, inflicting the greatest ecological impacts; Yangtze River Plain events were distinguished by extended duration. Vegetation photosynthetic responses differed by drought type: localized outbreak type droughts induced the highest sensitivity to soil moisture, yet displayed a declining interannual trend under low-threshold conditions (soil moisture percentile q ≤ 10). In contrast, under high-disturbance migratory type droughts, vegetation sensitivity weakened under highly correlated scenarios. Mechanistic analyses further revealed that topographic factors and vegetation functional traits amplified the effects of quasi-stationary type droughts on photosynthetic activity; net surface radiation and land-use type exerted greater influence during localized outbreak type droughts; whereas vegetation responses to high-disturbance migratory type droughts were predominantly governed by energy balance, with topographic modulation playing a relatively minor role.