Urban rainfall-runoff pollution is one of the main reasons for the deterioration of the receiving water quality. In this study, the lower reaches of the Meishe River on Hainan Island, China were adopted as the research area, and palladium (Pd) was selected as the target pollutant. The purpose of this study was to construct an input response model and to examine the Pd response relationship of receiving water bodies under multiple scenario changes of rainfall-runoff pollution combined with scenario analysis methods. The results showed that the mean absolute percent error (MAPE) and relative mean square error (RMSE) of the input response model were within 15%, which demonstrated the reliability of the model when applied to the simulation of the response of Pd in receiving water bodies to rainfall runoff. The dissolved Pd concentration in the receiving water body decreased in the following order: the moderate rain scenario > rainstorm scenario > the heavy rain scenario. The suspended Pd concentration in the receiving water body first increased and then decreased, and its decay rate was closely related to rainfall intensity and duration. Under the heavy rain and rainstorm scenarios, within 20 m downstream from the outfall, the occurrence time of the maximum suspended Pd concentration in the receiving water body was inversely proportional to the distance. The number of previous clear days was inversely proportional to the dissolved Pd concentration in the receiving water body and proportional to the suspended Pd concentration in the receiving water body. Under the short period of previous clear day scenario, the maximum suspended Pd concentration in each section of the receiving water body appeared earlier than that under the moderate and long periods of previous clear day scenarios.
Keywords: Input response model; Palladium; Rainfall runoff; Receiving water body; Response relationship.