Spatiotemporal shift of compound droughts toward China’s agricultural hubs: Insights from a multi−dimensional index integrating groundwater and ecological stress

Study region: China. Study focus: Conventional drought indices often overlook the coupling between subsurface storage and ecological stress, leading to incomplete risk assessments. This study addressed this gap by developing the Composite Extreme Drought Index (CEDI), a multi-dimensional framework that integrated the Standardized Drought-Wetness Alternation Index (SDWAI), Groundwater Drought Index (GDI), and Ecological Drought Index (EDI). Leveraging high-resolution hydroclimatic datasets from 2005 to 2024, we applied CEDI to diagnose the non-linear spatiotemporal evolution of compound droughts, aiming to identify regime shifts, migration pathways, and the driving mechanisms of drought propagation across different climatic zones. New hydrological insights for the region: The analysis revealed a paradigm shift in China’s drought risk landscape: (a) Compound droughts intensified markedly nationwide, driven by a structural regime shift post-2015. (b)A critical spatial migration was identified, which was that drought hotspots shifted eastward and southward, moving from the traditional arid Northwest to the densely populated, semi-humid agricultural zones in eastern China. (c) This shift was governed by a novel atmosphere-ecosystem bypass mechanism in the new hotspots, where escalating atmospheric demand triggers rapid ecological stress that overrode the slower groundwater buffering capacity. These findings highlighted a transition from erratic, natural variability to spatially clustered, high-intensity drought risks threatening regional food security.