Escalating hot-dry extremes in Southwest China Karst

Study region: Southwestern China of Hubei, Hunan, Guangxi, Guangdong, Yunnan, Guizhou, Sichuan, and Chongqing. Study focus: Compound hot-dry extreme events (CHDEs) are escalating disproportionately worldwide, posing significant challenges across various sectors. Yet, their driving mechanisms and characteristics at a regional scale remain largely uncertain. This study used a copula-based approach to construct the daily Standardized Compound Hot-Dry Index (SCHDI) to discern the intensifying trends of hot-dry extremes from 1963 to 2022, especially under different karst landscapes in Southwestern China. New hydrological insights for the region: SCHDI variations show an escalation of hot-dry conditions across most areas, with a notable increase in extreme hot, dry, and hot-dry events. There was a consistent increase in the frequency, duration, severity, and intensity of CHDEs, with larger magnitudes observed in non-karst areas. However, karst regions exhibited a higher escalation rate in intensity, especially over the most recent three decades. Land areas affected by less severe CHDEs (e.g., abnormal: -0.31%/year) show decreasing trends over 1993-2022, while the most extreme category (e.g., extreme: 0.34%/year) has increased. The areas affected by CHDEs showed a greater increase in trend slope compared to hot or dry events alone. Additionally, these trends are further influenced by large-scale circulation patterns. Our study highlights the role of karst landscapes in escalating hot-dry extremes in Southwestern China Karst.