Effect of typhoon rainstorm patterns on the spatio-temporal distribution of non-point source pollution in a coastal urbanized watershed

Extreme climate conditions, such as typhoon rainfall events, are common throughout coastal watersheds. However, despite the increasing interest in the impacts of rainstorm patterns on runoff pollution, research in this area is still inadequate. Therefore, an urban water quantity/quality model was constructed to evaluate the distribution characteristics of non-point source (NPS) pollution based on 12 typhoon rainstorm events that occurred within the 2008–2019 period. The rainstorm events were categorized as either an early pattern (EP), middle pattern (MP), or late pattern (LP), and the effects of these patterns on the NPS pollution of urban receiving water in Southeast China were investigated. For the 12 typhoon rainstorms under investigation, the results showed that 97.2% of the peak concentration time (PCT) of pollution indices occurred after the peak rainfall time (PRT), indicating a lag effect of the PCT, compared to the PRT. Additionally, it was observed that the EP rainstorm events are more likely to cause severe NPS pollution owing to their association with the longest lag time (135–180 min) and the earliest deterioration time (280–303 min). Moreover, the pollution load intensity (PLI) showed a strong response to urbanized land-use. In particular, the average PLI of the midstream watershed was found to be higher than that of other watersheds. These results provide useful information for the design of effective strategies for rainfall-runoff pollution mitigation in coastal urban watersheds in China.