Spatiotemporal evolution patterns and underlying formation mechanisms of monsoon rainfall across eastern China: A complex network perspective

Quantifying the evolution patterns and forming causes of monsoon rainfall is essential for prediction and mitigation of resultant hydrometeorological hazards. This study proposed a complex network-based framework to investigate these aspects over eastern China throughout the monsoon season. Based on the extracted heavy precipitation events (HPEs) at each grid within the monsoon season and twenty segmented phases, event synchronization and complex networks were utilized to construct HPE synchronized networks and HPE delayed networks, respectively. The former were utilized to identify monsoon rainfall subregions over eastern China, and further investigate the evolution rules of monsoon rainfall and associated hazard risks across the monsoon season. The latter were employed to investigate the spatial propagation patterns of monsoon rainfall within eastern China and individual subregions during their respective rainy seasons. Furthermore, the driving mechanisms behind the spatial propagation of monsoon rainfall within various subregions were explored by diagnosing the typical spatial propagation periods of monsoon rainfall and relevant regional atmospheric circulation anomalies. Results show that there are ten monsoon rainfall subregions over eastern China. Across these subregions, the monsoon rainfall undergoes seven sequential stages, including three stationary periods, two abrupt northward jumps and one southward retreat. As phases progress, zones with high hazard risks migrate within South China (SC), Yangtze River Basin (YRB), and Liaohe River Basin (LRB) with area first increasing and then decreasing from mid-April to early August. Diverse spatial propagation patterns of monsoon rainfall within various subregions arise from variations in the surrounding atmospheric circulation systems, resulting in anomalous wind patterns and moisture distribution. These anomalies, in turn, foster favorable conditions for monsoon rainfall to propagate along anomalous water vapor transport pathways. These findings advance our understanding of monsoon systems and associated hazard risks, shedding new light on their predictability.