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Coastal Hazard Assessments and Forecasts from Hurricane Florence

Hurricanes Florence and Michael caused extensive damage to coastal communities in North and South Carolina when they made landfall in September and October of 2018, respectively.

Erosion and widespread flooding due to the coupling of heavy rainfall and strong storm surge increased immediate and long-term hazards to shorelines, including densely populated areas, putting critical infrastructure at risk of future storm impacts and causing economic losses. The 2019 Disaster Supplemental Appropriation enabled the USGS Coastal and Marine Hazards and Resources Program to: (1) temporarily increase staff working on new rapid-response mapping techniques; (2) develop tools that more accurately forecast the intensity, location, and impacts of extreme events by accounting for compound impacts; and (3) map future coastal flooding and erosion hazards to guide infrastructure planning. This work will aid post-storm repair and recovery efforts in North and South Carolina by improving hurricane impact models for coastlines and updating assessments and models of coastal vulnerability to future storms.

To help stakeholders, such as the U.S. National Park Service and U.S. Army Corps of Engineers (USACE), rapidly assess storm impacts, plan field operations, and evaluate risks to natural resources, USGS developed new workflows (Over et al., 2021a) and techniques to evaluate and significantly improve the ability to use aerial imagery to measure coastal change along U.S. shorelines (e.g., Outer Banks and North Core Banks, North Carolina; Ritchie et al., 2021). Techniques for storing and processing imagery entirely in the cloud and on USGS High Performance Computing resources allow before and after comparisons of hurricane impacts to be available to stakeholders within hours after a storm to help facilitate response activities, as demonstrated immediately following Hurricanes Isaias and Laura. New imagery of North Core Banks has provided an unprecedented view of the effects of sound-side flooding and erosion, resulting in new concepts for the response to and recovery from major coastal events (Over et al., 2021b).

Screen shoot of HERA tool
Hazard Exposure Reporting and Analytics (HERA) tool.  

Federal agencies, emergency management offices, and local coastal planners rely on accurate storm forecasts to help make decisions that will safeguard lives and property along the coast. Many existing forecast models only account for singular weather phenomena. To more accurately forecast the impacts of hurricanes and storms, USGS developed tools that combine sophisticated models to provide more realistic scenarios. New techniques to predict the compound impacts (i.e., increased flooding) of ocean surge and riverine rainfall flows (Yin et al., 2021) are provided to NOAA NWS to enhance coastal flood forecasting of the NOAA National Water Model. USGS has also developed techniques to better model hurricane intensity and rainfall distribution (Porchetta, et al., 2020; Zambon, et al., 2021) and understand accompanying impacts of meteotsunamis, which can be generated during tropical cyclones and strong frontal systems and can cause severe damage and loss of life (Shi et al., 2020). To provide guidance for future infrastructure planning, USGS is mapping future coastal flooding and erosion hazards that can be expected due to sea-level rise and storms in North Carolina and South Carolina. These assessments include flood extent, depth, duration, and uncertainty for 28 unique sea-level rise and storm scenarios, future erosion hazard zones for 6 future sea-level rise scenarios, and depth to water table for 7 sea-level rise scenarios. Hazard zones will be translated into socioeconomic impacts and reported in the Hazard Exposure Reporting and Analytics (HERA)

 

Additional Resources: 

Total Water Level and Coastal Change Forecast Viewer

 

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