Chalmers Climate Dynamics Group

Atmospheric vapor pressure deficit (VPD) has intensified under global warming, yet its influence on soil moisture across depths remains unclear. Using multiple global monthly soil moisture datasets spanning the past decades, we combined pairwise and conditional Granger causality analyses to disentangle pathways linking VPD to surface (0–28 cm, SSM) and deep (28–100 cm, DSM) soil moisture. We identify widespread statistical directional dependence from VPD to both SSM and DSM, whereas the reverse relationships from soil moisture to VPD are comparatively weak. Across global land areas, we identified significant VPD–DSM relationships that remained after conditioning on SSM, here termed SSM-independent pathways, which were concentrated mainly in the mid- to high-latitude regions of the Northern Hemisphere and dominated in most forest and savanna ecosystems. Regions with SSM-independent pathways exhibit significantly higher vegetation greenness and evapotranspiration than neighboring SSM-mediated regions. Our findings reveal spatially heterogeneous patterns of land–atmosphere coupling and suggest an important role for vegetation-mediated water use in linking VPD to DSM variability.