Constitutive relationship of basin-scale rainfall-flood response in an urbanized watershed

Spatial and temporal rainfall characteristics have an important impact on flood response in urban areas. To explore the characteristics of flood response in an urbanized watershed, a distributed hydrological model (GSSHA) was constructed in the Jiuxiang River basin, Nanjing, China. Using the stochastic storm transposition method, a large set of rainfall processes was generated and used to simulate flood responses under different underlying surface scenarios. By employing machine learning approach to identify key spatial-temporal storm characteristics, a basin-scale flood response constitutive relationship was identified. GSSHA accurately simulated the characteristics of the flood response in the Jiuxiang River basin, with the spatiotemporal properties of flood-producing storms being crucial in the flood response. Urbanization weakened the dependence of the flood response on storm characteristics. The basin-scale constitutive relationship, with its high prediction accuracy (average relative error of approximately 0.154), provides a mathematical expression for understanding flood response in a small urban watershed. These insights will offer scientific supports for efficient flood prediction and forecasting in urban areas.