Emerging hotspots of spatial compound soil droughts in China's humid regions

This study is based on gridded soil moisture datasets used to characterize drought variability and synchronization across China. Standardized Soil Moisture Index (SSI) values were first calculated from the original soil moisture data to quantify drought conditions at each grid cell. Drought events were subsequently identified according to SSI-based threshold criteria and temporal persistence constraints. Based on the extracted drought events, an Event Synchronization (ES) framework was employed to quantify synchronous drought occurrences between grid cells and to construct directed drought synchronization networks. The resulting adjacency matrices and synchronization strength matrices were further used to calculate multiple complex-network metrics, including synchronization degree, in-degree, out-degree, divergence, clustering characteristics, and mean synchronization distance (MSD). These indicators were subsequently used for spatial visualization, temporal evolution analysis, and teleconnection pattern identification. To investigate the underlying hydroclimatic mechanisms associated with synchronous drought evolution, the Water Accounting Model-2layers (WAM-2layers) moisture tracking framework was additionally applied to quantify atmospheric moisture transport, moisture source–sink relationships, and anomalous moisture divergence/convergence processes during different drought stages.