Long-Term Dynamics of Surface-Water Structural Connectivity in a Highly Regulated Plain River Network of the Yangtze River Delta: Associations with Climate Variability and Land-Use Change

Long-term structural connectivity in highly regulated plain river networks remains insufficiently understood, particularly under concurrent climatic variability and land-use change. This study examined surface-water structural connectivity in Jiashan County, Yangtze River Delta, from 1990 to 2024 using graph-theory indices. The Integral Index of Connectivity (IIC) and Probability of Connectivity (PC) increased significantly, with slopes of 1.19 × 10−4 and 1.75 × 10−4 yr−1, respectively, and Pettitt change points in 2014 and 1998. Annual precipitation and rainy days were positively correlated with IIC (p < 0.05). After first differencing, annual changes in precipitation were strongly and positively correlated with changes in both IIC and PC (p < 0.001). Built-up land proportion (BLP) was positively correlated with both IIC and PC (p < 0.001). These findings highlight distinct long-term and interannual controls on structural connectivity and show that land-use change alone cannot predict the direction of connectivity change. The study provides a long-term basis for monitoring structural change in urbanizing plain river networks.