Degrading flood regulation function of river systems in the urbanization process

Highlights: • Two characteristic indicators were developed to estimate the flood regulation function in the delta plains. • Degrading flood regulation function exhibited significant structural and hierarchical differences in the Taihu Plain. • Impacts of urbanization and changes in the river systems on the change in the flood regulation function were inconsistent. This study developed the potential regulation capacity (PRC) and actual regulation capacity (ARC) to characterize the flood regulation function of river systems in the delta plains. Spatial autocorrelation and the grey relational analysis were then employed to investigate the spatial-temporal change of the flood regulation function in the urbanization process, of which the results revealed its spatial coupling and quantitative relation with the urbanization process and river systems changes in the Taihu Plain. The results indicated that: (1) the PRC exhibited a 20.3%-decrease during the 1960s to the 2010s, though its change exhibited significant structural and hierarchical differences. The global distributions of the PRCs all presented insignificant clustered characteristics, and the local distribution of smaller PRC regions with a high flood risk was stable; (2) the ARC exhibited a 33.2%-reduction in the recent 50 years, and its decrement also exhibited an accelerating trend. The global ARC distribution changed from significant clusters to insignificant aggregations, and the local distribution range of the smaller ARC regions with a high flood risk gradually increased; (3) the spatial coupling degree between the change in the PRC and the urbanization process was greater than that between the change in the ARC and the urbanization process, and the effect of urbanization on the change in the PRC was also larger than the change in the ARC; (4) the spatial coupling degree between the changes in the ARC and the river systems was greater than that between the changes in the PRC and the river systems, though the impacts of the river systems changes on the change in the PRC were larger than that on the change in the ARC. Therefore, the developed indicators based on limited and available information can serve as references for planning effective flood control strategies in the delta plains.