Changes and driving factors of compound droughts in China based on the soil-atmosphere compound drought index

Study region: China Study focus: Soil-atmosphere compound droughts, driven by high vapor pressure deficit (VPD) and low soil moisture (SM), significantly threaten vegetation growth. However, there remains a critical gap in quantitatively assessing the spatiotemporal patterns and driving mechanisms of these compound drought events in China. This study constructs a Soil-Atmosphere Compound Drought Index (SACDI) using SM and VPD data spanning 1982–2020, aiming to characterize the spatiotemporal evolution and driving factors of soil-atmosphere compound droughts across China. New hydrological insights for the region: This study yields several new hydrological insights into compound droughts in China. The identification of drought-fluctuation-wet evolutionary phases (1982–1991: slope=−0.0235/a, p < 0.05; 1992–2006: slope=0.0015/a, p > 0.05; 2007–2020: slope=0.0529/a, p < 0.01) reveals that compound droughts follow long-term hydroclimatic cycles, with negative slopes reflecting drought intensification and positive slopes reflecting alleviation. Persistent hotspots in the Continental River Basin (CRB), Songhua and Liaohe River Basin (SLRB), and Huai River Basin (HRB) indicate basin-specific hydrological vulnerability, affecting river discharge, soil moisture, and water management. Most basins face frequent short compound droughts, whereas Northeast China and southern CRB endure prolonged hydrological stress, highlighting spatial heterogeneity. Attribution analysis shows temperature (22.92 %), atmospheric circulation (22.09 %), and precipitation (17.73 %) as key drivers, implying that warming and circulation anomalies could exacerbate hydrological risks. These findings provide a solid basis for basin-targeted strategies to mitigate compound drought impacts on regional water systems.