Coasts represent some of the most dynamic and complex natural systems on Earth and are of outsized importance, relative to their area, for national and global economies. Nearly half of the global population lives within 100km of a coast and up to 90% of the world’s international trade passes through coastal infrastructure. Coastal zones sit at the nexus of societal and environmental challenges: Urbanization of coastal regions is expected to continue while risks from extreme events, sea level rise, groundwater salinization, and coastal erosion are increasing due to climate change. These intersecting challenges motivate a need for Earth system models (ESMs) that can represent coastal systems in detail to better understand the risk to and resilience of coastal cities arising from climate change and increased urbanization.  

Recent advancements in computational capability have enabled new ways of representing coastal systems in ESMs, such as the Department of Energy’s Energy Exascale Earth System Model (E3SM). While improvements have been made to the parameterization and representation of coastal processes, the impacts of these changes can be hard to assess at a process level. Furthermore, urban systems remain at the sub-grid scale for all but the highest resolution configurations of ESMs and therefore are highly parameterized. These limitations prevent a detailed understanding of coastal processes, their interactions with coastal cities, and the individual hydrologic processes that drive responses to extreme events or determine the success or failure of proposed mitigation and adaption interventions.

This project will address these limitations by developing a comprehensive water tracking system throughout E3SM. This tracking system will also provide the capability to simulate water isotope ratios, which are commonly used tracers of hydrological processes. Existing water isotope ratio observations will be compiled to validate the E3SM water isotope and tracer capability. Next, the new water tracer capability will be used to investigate the representation of coasts and their response to urbanization and extreme events in E3SM. The new water tracer capability will provide new ways to compare model simulations with tracer observations and enhance confidence in coastal and urban process representation in E3SM. The proposed research activities will enhance the E3SM's capability to track water sources, sinks, and transport throughout the hydrological cycle and across model components, ultimately improving our understanding of urban-coastal system interactions. By connecting this new tracking system to the existing capabilities, the enhanced E3SM can be utilized to study coastal change, extreme event susceptibility, and urbanization impacts on precipitation and flooding, and potential solutions for increasing coastal city resilience. E3SM simulations will be conducted in both idealized coastal-urban settings, as well as a case study of Houston, TX using data from the TRACER ARM campaign. The new framework has enormous potential to advance our understanding of the hydrological cycle in both natural and urbanized coastal systems and enable E3SM to answer a broad set of coastal-urban questions.