Human-induced intensification of subsurface soil moisture drought

Anthropogenic climate change has intensified soil moisture droughts worldwide, but how this intensification manifests in the spatiotemporal evolution of soil droughts’ vertical structure remains insufficiently understood. We develop a Lagrangian four-dimensional (longitude, latitude, depth, and time) tracking framework to identify contiguous drought events in both space (horizontally and vertically) and time. We reveal a distinct drought type, i.e., deep droughts. These events exhibit bottom-heavy, iceberg-like morphologies, with moisture deficits that are more extensive in deeper layers than in surface soils. Deep droughts account for approximately one-quarter of all events, yet they are largely overlooked by surface-focused soil moisture monitoring. Reanalyses and climate models consistently indicate that the duration and intensity of deep droughts have increased markedly over the past four decades, and that these increases are attributable to anthropogenic climate change. Future projections further indicate that deep droughts will become more persistent and severe globally, with the stronger amplification in deeper soil layers under higher-emission scenarios. Hidden below the surface, deep droughts challenge satellite-based agricultural drought monitoring, potentially leading to an underestimation of drought impacts on ecosystems.