The interactions between atmospheric and soil dryness are complex. Nevertheless, their influence on vegetation vulnerability and its evolutionary patterns has not been fully elucidated. To bridge this gap, we developed a novel probabilistic framework based on set intersection and union theory to disentangle the individual and interactive effects of soil moisture (SM) and vapor pressure deficit (VPD) on the Normalized Difference Vegetation Index (NDVI). Using this method, we quantified the strength, relative contribution, and temporal dynamics of SM-VPD interactions. The results revealed that: (1) Across Mainland China, excluding the permafrost regions of the northwest, the interaction between VPD and SM primarily exerted an inhibitory effect on NDVI, and this interaction intensified with increasing dryness severity. (2) Moreover, the relative contribution of this interaction to vegetation changes increased under more severe dryness conditions. (3) Spatially, the strength and contribution of the interaction showed significant increasing trends predominantly in northeastern China, while decreasing trends dominated in central and southern regions. Conversely, the individual effects of SM and VPD predominantly exhibited significant decreasing trends in the northeast and increasing trends in central and southern China. (4) In regions characterized by intensified land-atmosphere coupling, both the interaction strength and its contribution generally increased, whereas the individual effects of SM and VPD decreased. Overall, the dynamic changes in the interaction were found to be primarily associated with land-atmosphere coupling.
Wei et al. (Mon,) studied this question.