Vegetation increasingly controlled by atmospheric dryness rather than soil moisture

Terrestrial vegetation regulates global carbon cycling and climate through responses to water availability. Yet, it remains unclear whether soil moisture (SM) or atmospheric dryness (vapour pressure deficit, VPD) dominates vegetation responses and, more critically, how their relative influence changes over time, limiting predictions of ecosystem–climate feedback under warming. Here we analyse satellite-derived vegetation variability over the past four decades using an explainable artificial intelligence framework that disentangles nonlinear hydroclimatic driver contributions. We show SM dominates vegetation variability in most regions. However, VPD influence has strengthened while SM influence has weakened over time. These changes highlight an asymmetric transition with more SM-dominated ecosystems shifting towards increasing VPD control than vice versa. Changes in the mean and variability of SM and VPD drive this transition by altering plant water-stress responses. Continued warming will probably intensify this pattern as rising VPD and more frequent extreme events strengthen atmospheric constraints on vegetation.