Nature Geoscience, Published online: 10 September 2026; doi:10.1038/s41561-026-02082-2 Our global analysis of multi-source, multilayer soil moisture datasets shows that droughts become particularly damaging when moisture deficits occur simultaneously throughout the soil profile, eliminating vertical hydrological buffering. These vertically compound droughts have intensified across much of the globe and pose a growing threat to carbon uptake in forests and croplands.