Integrating Compound Flood Conditions Through 2D Hydraulic Modeling for Simulating Flood Risk Processes in Coastal Cities

Abstract:

Flooding events, which are the result of single or multiple flooding mechanisms happening at the same spatial and temporal scales, pose a significant threat to citizens and infrastructure. Compound inundation models have been gaining increasing attention, as the impacts of combined flooding mechanisms such as rainfall, tides, and storm surges exacerbated by climate change and sea level rise, have been unprecedented in coastal cities. Recent technological and scientific advancements support the continuous development of sophisticated and accurate numerical models to better understand flood hazard interactions (pluvial, fluvial, coastal, and groundwater flooding). Although the development of compound inundation models is a realized necessity, flood modelers face a series of challenges tied to the model’s level of complexity, data needs, performance, and code constraints to couple processes. In this contribution, we present the interactions of rainfall-runoff, coastal surge, and groundwater flooding mechanisms by using a combined hydrologic and hydraulic model (FLO-2D) as a base model to couple a 1D storm drain system (EPA SWMM) and groundwater model (MODFLOW-2005) in an iterative manner to simulate rainfall-runoff, coastal surge, and groundwater flood processes. The compound flooding methodology is applied in two major coastal cities, Miami (USA), and Palermo (Italy). In addition, stochastic and empirical statistical analysis support the identification of specific rainfall types that trigger dominant flooding mechanisms, stationarity, nonstationarity, and trends in the rainfall time series, ultimately leading to the assessment of current compound flooding conditions, and climate change scenarios. This study contributes to the field of hydroinformatics by improving flood level estimations when the interconnectivity (or nonlinearity) of events is determined between the physical processes to assess the increasing risk of compound flooding in coastal cities from a holistic perspective.