Tackling the Triple Threat: An Integrated Modeling Approach to Assess Compound Flood Risk in Coastal Cities

The recurrence of flood events has increased the vulnerability of major coastal cities to the compound triple threats of flooding, i.e., pluvial flooding, riverine flooding, and coastal flooding driven by storm surge. Climate change further exacerbates this challenge by introducing the additional risk of sea level and a growing number and intensity of storm events. This study introduces a multi-hazard scalable time sensitive high-resolution flood modeling approach that predicts the impacts of compound flooding in the Boston Metropolitan area and Cambridge. This highly impervious urban area is subjected to pluvial flooding from extreme precipitation, riverine flooding from the Charles River, and storm surge driven coastal flooding from Boston Harbor. First, precipitation data were generated and downscaled to the study site using the Coupled Hurricane Intensity Prediction System (CHIPS) model. Second, storm surges for the coastal boundary of the study area (i.e., Boston Harbor) were simulated utilizing the Advanced Circulation Model (ADCIRC). Third, the outputs from CHIPS and ADCIRC in conjunction with a coarse-resolution digital elevation model (DEM) were used as an input to the LISFLOOD-FP model to simulate the water surface elevations in the riverine and estuarine reaches of the rivers, which served as an input to the high-resolution hydrodynamic model, that was built using ICM software. Next, the downscaled precipitation data along with the riverine and coastal boundary conditions obtained from the previous models were implemented in ICM with high-resolution grid to assess both the individual and compound impacts of the flood drivers mentioned above. Finally, flood risk assessments were conducted using a probabilistic analysis based on Monte Carlo simulation of tropical storms with the resulting Monte Carlo ensembles of wind and precipitation fields being cascaded into a final derived distribution of surface flood depths and implications for the urban landscape. This study proposes an integrated modeling framework designed to support researchers, consultants, and other stakeholders to make informed decisions in quantifying and mitigating compound flooding in urban coastal environments.