Thresholds for triggering the propagation of meteorological drought to hydrological drought in water-limited regions of China

Propagation thresholds that trigger a transition between meteorological drought and hydrological drought are poorly understood, which hinders effective establishment of drought warning systems and prevention measures. Here, prop-agation thresholds were assessed by firstly identifying drought events during 1961-2016 in the Yellow River Basin, China, subsequently pooling, excluding, and matching them, and finally assessing their threshold conditions by using a combined Copula function and transition rate (Tr) analysis. These results show that response time changed ac-cording to variations in drought duration and watershed characteristics. Importantly, response times increased accord-ing to the timescales over which they were studied; for example, the Wenjiachuan watershed recorded response times of 8, 10, 10, and 13 months when examined at 1-, 3-, 6-, and 12-month timescales, respectively. Additionally, the se-verity and duration of meteorological and hydrological drought events both increased when events were combined rather than studied individually. These effects were also amplified for matched meteorological and hydrological droughts by factors of 1.67 (severity) and 1.45 (duration), respectively. Shorter response times were identified in the Linjiacun (LJC) and Zhangjiashan (ZJS) watersheds, and correlated with their relatively small Tr values of 43 % and 47 %, respectively. Higher propagation thresholds for drought characteristics (e.g., 1.81 and 1.95 for drought se-verity in the LJC and ZJS watersheds, respectively) imply that shorter response times tended to have greater effects on hydrological drought events and lowered their Tr, and vice versa. These results provide new insight into propagation thresholds used for water resource planning and management, and may help to mitigate the effects of future climate change.

Automated summary

The propagation thresholds that trigger a transition between meteorological drought and hydrological drought in the Yellow River Basin, China were assessed. The results showed that response time varied according to drought duration and watershed characteristics. When meteorological and hydrological drought events were combined, severity and duration increased, and the effects were amplified. Shorter response times were observed in certain watersheds and were correlated with lower Tr values. Higher propagation thresholds for drought characteristics had greater effects on hydrological drought events. These findings provide valuable insights for water resource planning and management to mitigate future climate change effects.