Spatiotemporal features and driving factors identification of urban flood-season pollution phenomenon

• Published in: Journal of hydrology (Amsterdam) Vol. 661; p. 133581
• Main Authors: Li, Jiali, Mao, Jintao, Zhao, Hongtao, Peng, Siyuan, Hang, Xiaoshuai, Feng, Jieyan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.11.2025
• Subjects: Flood-season pollution; Pollution characteristics; Rainfall events; Three-dimensional fluorescence; Urban water environment; Three-dimensional fluorescence; Urban water environment; Pollution characteristics; Flood-season pollution; Rainfall events
• ISSN: 0022-1694
• DOI: 10.1016/j.jhydrol.2025.133581

[Display omitted] •Urban river water quality deterioration is increasingly linked to rainfall events.•Historical data and extended time-series field observations were integrated.•Urban FSP process showed a bimodal pattern, with the 2nd peak being dominant.•The intensity, duration, and dynamic sources differ markedly between the peaks.•Derived the relationship between illegal connection probability and river RPI. With the extensive implementation of control measures for industrial point sources, domestic sewage pollution, and the broad adoption of Low Impact Development facilities, urban river water quality deterioration has increasingly been linked to rainfall events worldwide. Notably, this challenging phenomenon, known as flood-season pollution (FSP), is inadequately addressed in the new phase of precise water environment governance. Hence, this study investigates the process of river water quality decline and recovery during rainfall impact events (including the initial rainfall event and the subsequent 2 days) in Binhu District, Wuxi City, a typical plain river network area, using three-dimensional fluorescence tracing of dissolved organic matter (DOM). The results indicate that precipitation pollution intensity (RPI) of urban rivers surged significantly during flood seasons, with the monthly average maximum values of RPINH3-N and RPITP peaking at 12.6 and 6.0, respectively. Furthermore, the pollution process exhibited a bimodal characteristic, with Peak 1 (0.98 < RPI < 1.10) reaching 1.61 – 2.36 times the pre-rainfall level, occurring approximately 30 min after the rainfall began. Peak 2 (1.75 < RPI < 2.11), reaching 4.02–7.56 times the pre-rainfall level, followed the cessation of the initial rain and persisted for over 12 h. Notably, Peak 1 reflects the first flush of surface runoff and domestic pollution, while Peak 2 is formed due to the delayed impact of runoff. In cases of subsequent rainfall, the immediate effect of domestic sewage pollution would intensify Peak 2, prolonging its high RPI over an extended period and constituting the primary process of FSP. Additionally, PARAFAC analysis revealed that variations in pollution peaks were primarily driven by changes in surface runoff (39.7 ± 13.1 %) and domestic sewage (35.8 ± 10.4 %), while internal pollution (23.8 ± 4.5 %) remained stable throughout the process. These findings offer key insights into urban FSP characteristics and divers as a scientific basis for FSP governance.