I4.3 Coastal modeling through novel ocean developments in E3SM

Coastal climate change evolution will affect approximately 40% of the population who live in communities directly impacted by coastal flow-induced processes. Decadal scale evolution fundamentally depends on the flow of water across range of scales spanning from the deep ocean (1 deg) to geomorphological scales of shoreline evolution (<100m) where ocean, river, and land meet. The opportunity to resolve coastal system evolution is now possible because of improved high-performance computing resources and advanced multiscale algorithms. In particular, the unique unstructured grid capabilities of the Model for Prediction Across Scales Ocean (MPAS-O) allows model resolution to be applied in regions of interest without resorting to statistical or “box” models within the DOE Energy Exascale Earth System Model (E3SM). MPAS-O provides the opportunity to simulate a range of coastal processes. Planned process developments leveraging rapid resolution change from the global ocean into the coast include simulation of wind waves, sediment transport, and wetting and drying for flooding. This will allow coastal process simulations such as: flooding due to long- term effects of sea level rise and short-term effect of hurricanes and their associated storm surges arising from wind waves; salinity intrusion into coastal water supplies; sediment transport and shoreline evolution; and transport of heat and nutrients from coastal shelf waters to the deep ocean, e.g., mediating production of algal biomass; assessment of mixing and onshelf coastal currents that affect heat fluxes to melt ice sheets and increase sea level rise; etc. Within the E3SM, coastal flows simulated with MPAS-O are subject to evolving drivers such as atmospherically produced hurricanes and land-generated flooding and sediment transport due to stormwater off the land. Improvement in representation of waves and tides in the ocean will allow for the quantification of the balance of wave-tide-river forcing in determining the stability and evolution of coastal systems under future forcings. Ongoing coastal ocean capability developments in E3SM are opening up new opportunities to resolve the climate at the coast.