New flood hazard products to support coastal climate adaptation planning in Humboldt County, California

Across the US, coastal communities face increasing threats from flooding, erosion, and rising groundwater tables due to accelerating sea-level rise and changing storm patterns. CoSMoS is a dynamic modeling approach that allows for detailed projections of coastal flooding due to both future sea level rise and storms. It is integrated with long-term coastal evolution (i.e., beach changes and cliff retreat) over large geographic areas (100s of kilometers).

CoSMoS models all the relevant physics of a coastal storm (e.g., tides, waves, and storm surge), which are then scaled down to local flood projections for use in community-level coastal planning and decision-making. Rather than relying on historical storm records, CoSMoS uses wind and pressure from global climate models to project coastal storm impacts under changing climatic conditions during the 21st century. Projections of multiple storm scenarios are provided under a suite of sea-level rise scenarios. These options allow users to manage and meet their own planning horizons and specify degrees of risk tolerance.

Products and web tools have been used for a variety of coastal climate vulnerability and adaptation activities. Case studies highlight some of the ways in which the tools and data have been used, including:

• Sea level rise vulnerability assessments and coastal adaptation planning
• Municipal plans (e.g., General Plans, Hazard Mitigation Plans, Local Coastal Programs)
• Emergency management
• Infrastructure or capital investment plans
• Natural resource management/restoration plans
• Public engagement and communication

Access

Products are available as geospatial data downloads via the USGS ScienceBase Catalog, and via two interactive web tools:

• All CoSMoS geospatial data downloads are available here
• NEW* Humboldt County downloadable flood products direct link
• Hazard Exposure Reporting and Analytics (HERA) web tool: www.usgs.gov/apps/hera (Humboldt flood data available by end of December)
• Our Coast Our Future web tool: www.ourcoastourfuture.org (Humboldt County flood data available early Feb 2025)

Coastal erosion (bluff retreat and shoreline change) and rising groundwater hazard products are also available for all of California.

Technical Advancements

CoSMoS in Northern California has been updated to use 2-dimensional (2D) XBeach models to map projected flood hazards along the complex coastline. While the 2D models are more computationally expensive, the outputs yield more continuous and directly mappable hazards along the many coves, cliffs and beaches of Northern California, without the processing time and potential artifacts from merging 1D model output. Information about the methods are detailed in O’Neill et al. 2024 (open access).

Flood modeling for remaining areas of Northern California are underway, with Del Norte County anticipated in early Spring 2025.

Training and Technical Assistance

Interested in more information? Contact Maya Hayden (mkhayden@usgs.gov) for information on upcoming training opportunities and to request technical assistance.