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Three new studies from USGS and partners use an advanced coastal-storm modeling system to deliver fine-scale projections of wave behavior, flood exposure, and storm hazards in the Pacific Northwest's Salish Sea. 

Computational domain and bathymetry of the Salish Sea hydrodynamic model
Figure showing (a) Computational domain and bathymetry of the Salish Sea hydrodynamic model, and (b) Locations of National Oceanic and Atmospheric Administration (NOAA, red triangles) and U.S. Geological Survey (USGS, green triangles) water level measurement stations.

The Salish Sea, a large semi-protected estuary on the Washington and British Columbia coast, is an ecologically vital region that is home to more than 8 million residents—a population that is anticipated to double by 2060. Partially exposed to the northeast Pacific Ocean, its more than 7,400 kilometers (4,600 miles) of coastline are threatened by flooding, erosion, and ecosystem disruption as sea levels rise.

Addressing the need to forecast flooding and other coastal change impacts over large geographic areas, the new studies employed the Puget Sound Coastal Storm Modeling System (PS-CoSMoS). This innovative tool is designed to dynamically downscale future climate scenarios, including changes in wind and pressure fields, to compute regional water levels, waves, and compound flooding over large geographic areas with high spatial resolutions. 

Modeling of extreme water levels 

One of the new studies developed a regional two-dimensional model to simulate water levels accounting for tides, as well as non-tidal residual including sea level anomalies, inverse barometric pressure, high winds, and other processes. This research reinforces the importance of resolving remote and local drivers of extreme water levels and natural variability over decadal timescales to define extreme water level recurrence across the Salish Sea important to long-term coastal hazard planning.

Understanding and resolving extreme coastal water levels is critical to assessing the future coastal impacts anticipated with changing atmospheric and ocean dynamics. Spatial variability in extreme water levels can be captured by water level gauges, but these sites are few and far between; numerical models can quantify that variability and fill in the gaps. Models and improved empirical data also help evaluate the relative importance of the environmental forcing terms leading to extreme water levels, which are important to forecasting future conditions related to climate change. 

Modeling of wave generation and propagation 

Another study focuses on creating accurate, high-resolution wave statistics for regional hazard mapping and planning.

Characterized by its glacially carved landscape of narrow straits, islands, sills, and basins, the Salish Sea experiences storms with wind speeds comparable to hurricanes and significant wave action that contributes to flooding at high water levels. This wave activity also affects the erosion of shorelines, bluffs, and marshes, influencing vital habitats for shellfish, forage fish, and salmon. Furthermore, it impacts recreational and commercial boating activities crucial for accessing the numerous islands in Puget Sound.

Dynamic modeling of coastal compound flooding hazards 

Figure showing example output from PS-CoSMoS model for Birch Bay, Washington
Example output from PS-CoSMoS model for Birch Bay, Washington. Panel (A). Progressing storm extent for different storm frequencies for a sea-level-rise scenario of 50 cm. Panel (B). Progressing storm extent for different sea-level-rise scenarios for a storm frequency of 50 years. Panel (C). Water depth for a storm with a storm frequency of 50 years and 50 cm sea-level rise. Panel (D). Duration of the flooding for a storm with a storm frequency of 50 years and 50 cm sea-level rise.

The focus of this cutting-edge research is to advance robust and computationally efficient approaches specifically tailored for resolving the coastal compound flooding components in complex estuary environments. The study's application extends to the Puget Sound region of Washington State and the greater Salish Sea, where the implications of climate change on coastal hazards are of paramount importance.

The PS-CoSMoS modeling system provides coastal planners with accurate projections of storm hazards and flood exposure for recurring flood events, spanning from annual occurrences to those with a 1-percent annual chance of flooding. These projections can be used to prioritize and protect critical infrastructure and valued ecosystems.

Altogether, these new studies contribute not only to the scientific understanding of coastal dynamics in the Salish Sea, but also equip communities and decision-makers with tools to proactively address the challenges posed by climate change. As coastal regions worldwide grapple with the escalating impacts of environmental change, the integration of cutting-edge technologies like PS-CoSMoS becomes increasingly crucial for fostering sustainable and resilient coastal communities.

Read a related press release from Washington Sea Grant.

Visit the Washington Sea Grant CoSMoS website.

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