Spatiotemporal patterns and propagation mechanism of meteorological droughts over Yangtze River Basin and Pearl River Basin based on complex network theory

Investigating spatiotemporal pattern and propagation mechanism of meteorological drought is of great significance to develop early warning system for drought-affected regions and other drought types. In this study, the spatiotemporal characteristics and evolution trend of meteorological drought represented by the standardized precipitation evapotranspiration index (SPEI) during 2016–2021 across the Yangtze River basin (YZRB) and Pearl River basin (PRB) were analyzed. The drought spatial synchronization extent and propagation mechanisms (i.e., propagation source, sink, direction, strength and distance) were also investigated through constructing the undirected and directed complex networks, respectively. The results indicate that during 1961–2021, meteorological droughts in the middle and lower reaches of the YZRB and PRB present an alleviating trend, while droughts over their upper reaches that are relatively far from coastal regions are aggravated. The drought synchronization extents at the spatial scale are classified into seven communities, where the drought events within the same community are more likely to occur synchronously and their characteristics are more similar. Moreover, the drought propagation source regions are mainly distributed over the eastern coastal regions of the YZRB, the upper coastal regions of the PRB and the headwaters of the YZRB, from where droughts start to propagate along the WSW (or WNW) direction, NE direction and ESE direction to interior regions, respectively. The sink regions are mostly distributed in the YZRB and PRB middle reaches and the southwestern parts of the YZRB upper reaches. Meteorological drought events in most regions have a propagation distance of hundreds of kilometers. This study provides new tools and insights on drought propagation and prediction and can help policy-makers formulate advanced preventive measures.