Spatiotemporal characteristics of drought in the Southwest Karst Rocky desertification zone, 1992–2022

Drought threatens ecosystem resilience in the fragile karst rocky desertification zone of Southwest China. Based on meteorological observations from 1992 to 2022, this study assessed drought dynamics using the Reconnaissance Drought Index (RDI), Standardized Precipitation Evapotranspiration Index (SPEI), and Standardized Precipitation Index (SPI), cross-validated against the Temperature Vegetation Dryness Index (TVDI) and disaster records from the Emergency Events Database (EM-DAT). The results indicate that: (1) While all indices identified major events including the 2009 severe drought, SPEI and RDI demonstrated higher sensitivity to warming-driven compound water deficits than SPI, suggesting that standard thresholds serve as a conservative ecological risk baseline; (2) Temporally, a pivotal regime shift around 2002 transitioned the region to a persistent water deficit phase driven by weakened moisture transport and potential evapotranspiration amplification, followed by heightened climatic instability with rapid drought and flood alternations in recent years; (3) Spatially, drought clustering in Eastern Yunnan, Southwestern Guizhou, and Western Guangxi overlaps with rocky desertification hotspots where the dual surface and subsurface hydrological structure exacerbates vulnerability; and (4) Seasonally, droughts concentrated in spring and autumn, disrupting critical phenological stages including regreening. These findings highlight the geological and climatic coupling mechanism, underscoring the need for process-based water regulation and restoration strategies in geologically constrained environments.