Spatiotemporal Evolution of Flood-Waterlogging Events in Major Urban Agglomerations of China

A thorough understanding of the spatiotemporal characteristics of flood-waterlogging (FW) events in high-risk urban agglomerations is vital for climate change adaptation planning. In this study, based on daily precipitation data from meteorological stations in 11 urban agglomerations in China and a relative weight analysis method, the spatiotemporal evolution of FW events with different severities and their contributions to the frequency changes of overall events in these urban agglomerations during 1962–2020 were investigated. The results show that the southeastern urban agglomerations (e.g., Middle Reaches of the Yangtze River Urban Agglomeration, Yangtze River Delta, Pearl River Delta, and Beibu Gulf Urban Agglomeration) exhibit higher frequencies (exceeding 2.5 events yr⁻¹) and longer durations (more than 5.5 days) of FW events, whereas the northern and western urban agglomerations generally record frequencies below 1 event yr⁻¹ and durations shorter than 4 days. Furthermore, although most urban agglomerations exhibit decreasing trends in the frequencies of FW events with different severities during 1962–2020, the frequencies of special (extremely severe) FW events in the Yangtze River Delta (0.01 decade⁻¹) and heavy FW events in the Pearl River Delta (0.03 decade⁻¹) have shown an increasing trend. In the Pearl River Delta, heavy (34%) and moderate (33%) FW events dominate the increasing trend in the frequency of overall FW events, whereas light or moderate FW changes dominate in most other regions. Since 2000, both FW frequencies and durations have increased in many urban agglomerations. This study underscores the necessity of incorporating spatial differences and cumulative effects of precipitation into FW risk assessments, providing a scientific basis for regional flood mitigation strategies and sustainable urban planning.