Identifying the risk of urban nonpoint source pollution using an index model based on impervious-pervious spatial pattern

Abstract Efficiently evaluating the risk of urban non-point source pollution (urban-NPS) using only a few parameters is crucial to its management and control, especially in engineering. However, the huge spatial heterogeneity of urban-NPS induced by the high spatial heterogeneity in land use, surface infiltration and surface micro-topography, make it difficult. A new index model composed of transport and source factors was proposed to evaluate the urban-NPS risk. An urban catchment in southern China served to demonstrate the proposed method. The ability of runoff output was characterized by the transport factor in which the impervious-pervious surface spatial pattern, imperviousness ratio and rainfall were taken into account. The pollutants output capacity was represented by source factor where the imperviousness ratio and source-sink transformation resulting from rainfall were considered. Results show the proposed index can identify and evaluate the risk of urban-NPS at both urban parcel scale and catchment scale. The percent bias (PBIAS) of runoff volume helped to assess the performance of the index. PBIAS (1–86%) between the proposed method and the observed runoff was much lower than that (27–448%) between the traditional runoff coefficient method and the observed runoff. These suggest that the proposed index offers a new way of assessing urban-NPS risk.