Urban flood response analysis for designed rainstorms with different characteristics based on a tracer-aided modeling simulation

The frequent occurrence of urban floods has severely affected urban public safety and restricted the sustainable development of the social economy. Studies have confirmed that extreme rainstorms are determining factors for the cause of urban floods. Additionally, the rainstorm pattern could be adopted to measure the temporal change in rainstorm intensity, and there may be differences in the process of urban flood, even if the rainstorm amount and return period are the same. The in-depth analysis of urban flood disaster levels in response to rainstorms with different characteristics is of substantial significance for managing unfavorable situations and implementing flood mitigation measures. Therefore, a tracer-aided urban flood model was developed to study the impact of rainstorm patterns on urban flooding. Based on the source tracking results, the direct and indirect connections were established between different areas of the urban system, their relative importance in the urban system was explored, and the response of urban flood processes to different rainstorm patterns from the perspective of flood source areas was analyzed. This study presents a modeling task for the Longkungou drainage district of Haikou City. Simulations were performed for 21 designed rainstorm events, in which the characteristic differences in rainstorm distribution are reflected in the return period, rainstorm patterns, and peak coefficients. The results indicate that in the case of the same rainstorm amount, the unimodal patterns, Modes II (middle peak) and III (late peak), are the most unfavorable situations for the flooded area. In addition, rainstorms with bimodal patterns also had different effects on the flood volume: Models VI and V had the largest and smallest flood volume, respectively. The source tracking results further showed that the formation of flood volume in the source area of the catchment is a comprehensive effect of regional characteristics and rainstorm patterns. The source area flood volume of catchments located upstream were not sensitive to the response of rainstorm patterns, and catchments in urban system with weaker drainage systems were more sensitive than that to the response of rainstorm patterns. This study provides theoretical insights for early warning of urban flooding, implementation of urban flood mitigation strategies, and flood risk management.