Propagation characteristics of meteorological drought to hydrological drought in China

Abstract

In the study of drought propagation, understanding the relationship between meteorological and hydrological drought is crucial for assessing the formation and evolution of drought. The traditional Pearson correlation coefficient mainly reflects the statistical correlation between variables, but this correlation may not necessarily reveal potential causal mechanisms. In contrast, convergent cross mapping (CCM) can better elucidate the dynamic mechanisms of drought propagation by capturing causal relationships between variables. This study reveals key insights into the dynamics of drought propagation by combining causal inference and watershed-specific assessments. The main findings include: (1) Over the past 58 years, meteorological and hydrological droughts have occurred frequently in China. Hydrological droughts are more severe in the northern regions, with their duration approximately three times longer than that of meteorological droughts. Additionally, 27.34 % of the grids show a significant increase in meteorological drought, while 14.59 % show a similar trend in hydrological drought. (2) Meteorological drought is the primary driver of hydrological drought, and a significant unidirectional causal relationship exists between them. Specifically, 99.06 % of the grids across the country show a significant correlation, while 86.84 % display convergent causality. Moreover, CCM can identify nonlinear dynamics, thereby providing a more comprehensive explanation than linear correlation alone. In regions like the Pearl River Basin and Southeast River Basin, causality is stronger than correlation, suggesting that correlation could serve as a substitute for causality when exploring drought propagation time. (3) Compared to correlation analysis, causal analysis yields higher propagation rates and provides more reliable evaluations by reducing uncertainty. In addition, the northern basins are more susceptible to the impact of meteorological drought. These results provide valuable guidance for optimizing water resource management, enhancing drought early warning systems, and reinforcing water infrastructure in environmentally vulnerable basins.