Coupling the National Water Model to the Coastal Ocean for Predicting Water Hazards

Recent climate studies provide strong evidence that storms will generally have greater precipitation and that tropical cyclones will become more intense under future climate conditions. Additionally, recent flooding events (Hurricanes Matthew (2016), Harvey and Irma (2017)) remind us that prediction of water related hazards remains challenging, particularly when hydrologic (fresh water) flooding and coastal storm surge co-occur as a compound event. Significant progress has been made in modeling and prediction of the upland/hydrologic and coastal/storm surge zones, but the intermediate area where the two flooding sources overlap has only recently begun to receive more attention. With compound flooding occurrences expected to become more frequent, new approaches to modeling and prediction are needed in the intermediate zone between inland/upland flooding and storm surge.

Difficulties associated with modeling compound events are largely the result of independent development of hydrologic models and coastal surge / wave models. While these models may have the necessary boundary conditions, (e.g., coastal models can typically ingest riverine inflows and hydrologic models with appropriate physics can use coastal water levels as a downstream river boundary condition), they have typically been applied in situations in which the boundary conditions are predetermined, either from observations or from stand-alone model runs. However, such an approach is insufficient for applications that require concurrent modeling of both inland and coastal water movement, such as in real time nowcast / forecasting and rapid post storm assessments.

As a new project within the NOAA Integrated Ocean Observing System (IOOS) Coastal Ocean Modeling Testbed (COMT), we are tackling this critical challenge by developing coupling strategies for connecting the NOAA National Water Model to the storm surge model ADCIRC, which comprises the compute engine for NOAA’s ESTOFS and HSOFS coastal surge predictions. In this presentation, we outline the major challenges associated with coupling large-scale hydrologic to coastal models, the current state of coupling strategies and implementations, and our general roadmap for the next few years in coupling hydrologic to coastal models.