Assessing Compound Flooding From Landfalling Tropical Cyclones on the North Carolina Coast

Tropical cyclone (TC) events are major drivers of compound flooding due to the interaction of wind-driven storm surge and TC rainfall. Traditionally, coastal flood risk models have only taken into account surge flooding, even though it is known that the role of rainfall-runoff is critical. There is limited understanding about the types of TC events that are capable of producing significant compounding and how site conditions at the coast affect the extent to which storm surge and rainfall-runoff interact. This study investigates a suite of historical TCs making landfall near the Cape Fear River Estuary, NC, through a loosely coupled physical modeling methodology in order to draw conclusions about the spatial and temporal patterns of storm surge and rainfall that are able to induce significant compound impacts. Results indicate that intense outer rain bands falling over inland portions of the study area can be a driver of river-surge compounding (increasing river levels by up to 0.36 m), while intense eyewall rainfall along the coast can result in localized compound impacts to coastal streams and tributaries if peak rainfall occurs near the time of peak storm tide. These localized compound impacts can result in defined interaction zones, where neither storm tide alone nor rainfall-runoff alone can fully explain the observed maximum water levels. These results provide insight about the relative timing and spatial patterns of rainfall and storm surge that are capable of inducing compound flooding during TC events. Key Points Compound flood impacts from historical TCs on North Carolina coast quantified through loosely coupled physical modeling method Spatial overlap and relative timing between rainfall, peak river flows, and peak storm tide are critical factors in observed compounding Both outer rain bands and inner core rainfall from TCs can be drivers of compound flooding