Spatiotemporal evolution of urban water bodies and their response to city development: A comparative analysis of northern and Southern China (1990–2023)

Study region This study focuses on 20 major cities in northern and southern China. The southern cities include Shanghai, Shenzhen, Guangzhou, Wuxi, Chengdu, Suzhou, Hangzhou, Wuhan, Nanjing, and Ningbo, while the northern cities are Beijing, Tianjin, Qingdao, Zhengzhou, Jinan, Xi'an, Yantai, Tangshan, Shenyang, and Dalian. The region spans diverse climatic conditions and hydrological settings, providing a representative context for analyzing long-term urban water body dynamics under rapid urbanization. Study focus This study investigates the spatiotemporal evolution of urban water bodies (UWBs) and their relationship with urban development. Multisource Landsat imagery, together with GDP and population data, were integrated using a U-Net deep learning model to extract water areas and conduct comparative analysis between northern and southern cities. This approach improves extraction accuracy over conventional water indices and enables consistent long-term monitoring across large spatial scales. New hydrological insights for the region This study reveals distinct long-term urban water-body trajectories between the northern and southern cities, together with substantial inter-city heterogeneity within both regions. After accounting for city-level heterogeneity and temporal dependence, region, GDP, and population were not statistically significant predictors of urban water-body area, indicating that these variables alone do not adequately explain the observed variation. The results therefore suggest that the observed north–south contrast reflects complex and city-specific water-body evolution rather than a simple socioeconomic gradient.