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.
Compound flooding, characterized by the co‐occurrence of multiple flood mechanisms, is a major threat to coastlines across the globe. Tropical cyclones (TCs) are responsible for many compound floods due to their storm surge and intense rainfall. Previous efforts to quantify compound flood hazard have typically adopted statistical approaches that may be unable to fully capture spatio‐temporal dynamics between rainfall‐runoff and storm surge, which ultimately impact total water levels. In contrast, we pose a physics‐driven approach that utilizes a large set of realistic TC events and a simplified physics‐based rainfall model and simulates each event within a hydrodynamic model framework. We apply our approach to investigate TC flooding in the Cape Fear River, NC. We find TC approach angle, forward speed, and intensity are relevant for compound flood potential, but rainfall rate and time lag between the centroid of rainfall and peak storm tide are the strongest predictors of compounding magnitude. Neglecting rainfall underestimates 100‐year flood depths across 28% of the floodplain, and taking the maximum of each hazard modeled separately still underestimates 16% of the floodplain. We find the main stem of the river is surge‐dominated, upstream portions of small streams and pluvial areas are rainfall dominated, but midstream portions of streams are compounding zones, and areas close to the coastline are surge dominated for lower return periods but compounding zones for high return periods (100 years). Our method links joint rainfall‐surge occurrence to actual flood impacts and demonstrates how compound flooding is distributed across coastal catchments.
more » « less- Award ID(s):
- 1854993
- NSF-PAR ID:
- 10454705
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Earth's Future
- Volume:
- 8
- Issue:
- 12
- ISSN:
- 2328-4277
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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