An accuracy-improved flood risk and ecological risk assessment in an interconnected river-lake system based on a copula-coupled hydrodynamic risk assessment model

Understanding flood event-related risk in an interconnected river-lake system (IRLS) is a prerequisite for developing water resource management strategies and enhancing disaster resilience. Previous flood event-related risk assessments either hardly consider the context in which water diversion encounters flood events or hardly consider the physical process, stochastic analysis and multivariate interactions of flood event characteristics simultaneously, thereby resulting in a less reliable assessment of flood event-related risk. To resolve this limitation, a copula-coupled hydrodynamic risk assessment model (CHRAM) is proposed to characterize the physical, multivariate, and stochastic nature of risk, improving the accuracy of risk assessment. In this study, CHRAM is capable of accurately quantifying flood event-related risks (i.e., flood risk and ecological risk) of the Nansi Lake Basin in the flood season under the operation of the eastern route of the South-to-North Water Diversion Project in China. Our findings revealed that the total flood volume (R-sum) and duration (T-d) of flood events were significantly sensitive characteristic indexes for flood risk and ecological risk. In addition, the security domains of flood risk (R-sum < 35 mm and T-d < 23 d) and ecological risk (R-sum < 50 mm and T-d < 27 d) were determined based on the analysis of the relationship between sensitive characteristic indexes and risk indicators. The results also showed that the impact of T-d on flood risk, ecological risk and flood-ecological combined risk was 3-14 times greater than the impact of R-sum. The occurrence probability of flood-ecological combined risk was smaller than that of flood risk but greater than that of ecological risk, with the corresponding maximum risk probabilities of 11.2%, 36.5%, and 4.7%, respectively. This study extends the current knowledge about risk assessment in IRLS and is beneficial to instruct the management of projects for similar systems.