Spatiotemporal changes and interconnections between meteorological and hydrological droughts in China over past 34 years

Understanding the evolution and lag effects of droughts is critical to effective drought warning and water resources management. However, due to limited hydrological data, few studies have examined hydrological droughts and their lag time from meteorological droughts at a daily scale. In this study, precipitation data were collected to calculate the standardized precipitation index (SPI), and runoff data simulated by the variable infiltration capacity (VIC) model were utilized to compute the standardized runoff index (SRI). The three-threshold run theory was used to identify drought characteristics in China. These drought characteristics were utilized to investigate spatiotemporal variations, seasonal trends, and temporal changes in areas affected by meteorological and hydrological droughts. Additionally, the interconnections and lag effects between meteorological and hydrological droughts were explored. The results indicated that (1) drought occurred during approximately 28% of the past 34 years in China; (2) drought conditions tended to worsen in autumn and weaken in winter; (3) drought-affected areas shifted from northwest to northeast and finally to southern China; and (4) the correlation between meteorological and hydrological droughts was lower in the northwest and higher in the southeast, with all correlation coefficients exceeding 0.7. The lag times between meteorological and hydrological droughts were longest (5 d) in the Yangtze River, Yellow River, and Hai River basins, and shortest (0 d) in the Tarim River Basin. This study provides a scientific basis for effective early warning of droughts.