A review of compound flood hazard research in coastal areas

Coastal areas frequently suffer from flood disasters, which is not caused by a single hazard, but a combination and interaction of multi-hazards. This study sorted out the definitions and mechanisms of compound flood, and systematically summarized the progress of compound flood research from two aspects: statistical model and dynamic numerical model. Compound flood arises from two or three of oceanographic (storm surge, tides, and waves), riverine/fluvial, and pluvial (precipitation leading to direct surface runoff) sources. Studies based on the statistical modeling focus on assessment of joint correlation for multi-variates. It can better understand the spatial and temporal variation of compound flood at a large scale, as well as their relationship with climate factors. The difficulties and future research trends are to construct the nonstationary statistical model of two and more hazards under a changing environment. Studies based on dynamic numerical models require the coupling of hydrology, oceanology, and hydraulic models with meteorological components (tropical cyclones, wind field, pressure field) as important boundary conditions. The modeling process is complex, time-consuming, and requires high computation, but it can clearly describe the evolution process of compound floods, and can be helpful for future scenario analysis. In the future, more attention should be paid to the mechanism of compound flooding in coastal low-lying areas. It is necessary to strengthen the research of long time series model simulation products in combination with climate change factors in the risk assessment of climate change and extreme complex events. In the service of the meteorological and marine forecast, it is proposed to strengthen the research on monitoring and early warning technique, as well as improvement of the dynamic framework, parameterization optimization of physical process, data assimilation, improvement of pattern grid resolution, and optimization of the ensemble prediction scheme. Under the background of global climate change and continuous urbanization, it is urgent to assess the integrated risk of compound flood in coastal areas by considering anthropogenic and climatic factors.