Investigating multitype drought propagation thresholds across the different climate regions of China

Drought is a common and severe natural hazard worldwide. Understanding its triggering mechanisms is pivotal for comprehending its propagation. However, the triggering mechanisms of multitype drought propagation in diverse climate regions remain unclear. This study presents the first exploration of the triggering mechanisms of multitype drought propagation in the different climate regions of China. ECMWF reanalysis 5th generation and normalized difference vegetation index (NDVI) data were utilized. Drought indices were applied to describe meteorological drought, hydrological drought, agricultural drought, and vegetation drought. The copula function and run theory were employed to estimate the propagation thresholds of multitype drought. The results revealed that (1) the Frank, Gumbel, and Student-t copula functions were optimal for combining different drought types. The generalized Pareto (GP) distribution, Weibull distribution (WBL), and logarithmic normal distribution (Log) were best for describing different types of drought characteristics. (2) The propagation thresholds for meteorological to hydrological and agricultural drought were lower than those for agricultural to hydrological drought. The propagation thresholds for agricultural to hydrological drought were notably greater in the temperate humid and subhumid region in Northeast China (SR-3) and the warm-temperate humid and subhumid region in North China (SR-4). (3) Vegetation drought was more difficult to trigger in forests and deserts than in grasslands and croplands. Vegetation drought was more difficult to trigger in the temperate and warm-temperate desert of northwestern China (SR-1) and the tropical humid region in South China (SR-7). These findings offer profound insights into drought propagation dynamics across various climates and into early warning, defense against, and forecasting of multitype drought.