Spatiotemporal Characteristics and Probabilistic Thresholds of Meteorological Drought Propagation to Surface Soil Drought in Sichuan Province, China

Daily drought propagation across contrasting landforms remains insufficiently characterized. We examined meteorological drought propagation to surface soil drought in Sichuan Province, China, using daily ERA5 meteorological data at 0.25° resolution and CSMX surface soil moisture data (0–10 cm) at 1 km resolution for 2000–2024. The CSMX data were aggregated by area averaging to the ERA5 0.25° grid. Standardized precipitation evapotranspiration and soil moisture indices (SPEI and SSMI) were combined with run theory, one-to-one event matching, and copula models. The 10-day SPEI correlated most strongly with provincial SSMI (r = 0.643); gridwise correlations ranged from 0.243 to 0.712. Annual surface soil drought days correlated strongly with moderate or more severe meteorological drought days (r = 0.71). The Sichuan Basin had the highest meteorological drought propagation and surface soil drought matching rates (50.24% and 73.57%, respectively). Most matched surface soil droughts began during meteorological droughts, with regional median propagation times of 6–8 days. Copula dependence varied by region and event attribute. At conditional quantiles of 0.50 and 0.70, meteorological drought duration and severity thresholds for the same surface soil drought attribute class were highest in the Southwestern Sichuan Mountains, followed by the Northwestern Sichuan Plateau and Sichuan Basin; rankings varied at 0.90. These findings highlight short propagation times and regional differences relevant to surface soil drought monitoring.