Drought events have become more frequent worldwide under ongoing climate change. However, how precipitation deficits evolve into runoff deficits across contrasting dry and humid climate regions, and which factors control this transition, remains insufficiently understood. This study takes five climate zones in China (arid, semi-arid, semi-humid, humid–semi-humid, and humid) from 1970 to 2020 as examples to explore the propagation process of drought and its key driving factors. We used the Standardized Precipitation Index (SPI), Standardized Runoff Index (SRI), maximum correlation coefficient method, Kendall’s test, and multiple linear regression to identify the drought propagation time (DPT), its dynamic changes, and its main influencing factors. The results indicate that DPT exhibits significant seasonal and regional variations: on a national scale, its peak occurs in winter (7.35 months) and its trough in summer (2.54 months); specifically, propagation times in humid regions are relatively short and stable, whereas those in semi-arid, semi-humid, and humid–semi-humid regions are relatively long and highly variable. Temperature (20.69% in spring; 16.67% in summer) and potential evaporation dominate in spring, autumn, and winter, while summer precipitation (9.38%) also has a significant impact. The El Niño–Southern Oscillation (ENSO) has the most significant impact on humid regions, increasing the model R2 from 34.6–37.2% to 43.7–45.0%. These results improve the understanding of drought propagation mechanisms across climatic regions, highlight the significant influence of ENSO on seasonal and regional variations in DPT, and provide a basis for regional drought early warning and water-resource management.
Fan et al. (Fri,) studied this question.