Integrating WRF Hydro into the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System: Application to Hurricane Florence (2018)

John C Warner1, Joseph B Zambon2, Ruoying He3, Zafer Defne4 and Christie Hegermiller1, (1)USGS Coastal and Marine Science Center Woods Hole, Woods Hole, MA, United States, (2)NC State University, Raleigh, NC, United States, (3)North Carolina State Univ., Raleigh, NC, United States, (4)US Geological Survey, Menlo Park, CA, United States
The impacts of storms on coastal systems, including erosion and flooding, result from many processes, such as extreme rainfall, winds, waves, and ocean surge. To improve our ability to predict these events, multiple and varied models need to be integrated to simulate atmospheric, hydrodynamic, wave, terrestrial, and hydrologic processes. The ability to couple this suite of models and resolve their individual and complex interactions is not well established. We developed the Coupled Ocean-Atmosphere-Waves-Sediment Transport (COAWST) Modeling System to simulate coastal storms and their impacts by coupling the hydrodynamic model ROMS, the atmospheric model WRF, the wave models SWAN, WAVEWATCH III, or InWave, and the Community Sediment Transport Modeling System. COAWST is open-source and community-developed, with an active user base, biennial trainings, and code distributed on GitHub. The system is extensively used to simulate many historical storm events and identify significant exchange processes.

We integrated the hydrologic model WRF-Hydro into the coupled system, allowing precipitation to be routed as overland flow to rivers and ultimately the ocean. This system was used to simulate Hurricane Florence (2018), a major storm that brought record-setting rainfall and flooding to the mid-Atlantic coast of the US. We demonstrate interactions of fresh water inflows with ocean surge, the total combined water levels as compared to observations, discuss complications, modeling strategies, and approaches to advance the modeling of coupled interactions. The model allows the analysis of the separate and combined effects of storm surge, rainfall, and riverine flooding during Florence, that can lead to improved flood preparedness. The ultimate goal of this effort is to provide sound guidance based on real-time flood and storm surge forecasting to stakeholders in coastal communities.