Drought Propagates Asynchronously Across Hydrological Compartments: Stage Differences in Propagation Time and Implications for Drought Monitoring

Drought propagation across hydrological compartments is not a synchronous process, yet stage‐specific differences between the Stage 1 (meteorological‐to‐soil link) and the Stage 2 (soil‐to‐groundwater link) remain insufficiently understood. Using China as a hydroclimatically diverse test domain, this study established a two‐stage drought propagation framework linking SPI, SSI and GWSA‐DSI and combined propagation‐time analysis with AC1 (first‐order autocorrelation) and partial‐correlation diagnostics. Results showed that drought propagated rapidly from meteorological to soil conditions, with lag times of 1.2–4.1 months, whereas propagation from soil drought to groundwater drought was consistently slower, with lag times of 2.6–5.9 months. The slower Stage 2 was characterized by generally lower short‐term temporal persistence and weaker conditional associations with concurrent hydroclimatic forcing. Antecedent soil moisture showed a strong and spatially consistent association with current SSI, whereas its relationship with GWSA‐DSI was substantially weaker and regionally heterogeneous. These findings show that drought propagation is stage‐dependent across hydrological compartments, with deeper storage responding more slowly. This process‐based asymmetry implies that rapid changes in near‐surface indicators do not necessarily indicate equally rapid development or recovery of deeper hydrological drought.