Generating Boundary Conditions for Compound Flood Modeling in a Probabilistic Framework

Abstract. Compound flood risk assessments require probabilistic estimates of flood depths and extents that are derived from compound flood models. It is essential to simulate a wide range of flood driver conditions to capture the full range of variability in resultant flooding. Although recent advancements in computational resources and the development of faster compound flood models allow for more rapid simulations, generating a large enough set of storm events for boundary conditions remains a challenge. In this study, we introduce a statistical framework designed to generate many synthetic but physically plausible compound events, including storm-tide hydrographs and rainfall fields, which can serve as boundary conditions for dynamic compound flood models. We apply the proposed framework to Gloucester City in New Jersey, as a case study, and the results demonstrate its effectiveness in producing synthetic events covering the unobserved regions of the parameter space. We use flood model simulations to assess the importance of explicitly accounting for variability in mean sea level (MSL) and tides in generating the boundary conditions. Results highlight that MSL anomalies and tidal conditions alone can lead to differences in flood depths exceeding 1 m and 1.2 m, respectively, in parts of Gloucester City. While we focus on historically observed events, the framework can be used with model output data including hindcasts or future projections.