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Computer modeling by USGS and the University of South Wales-Sydney predicts significant beach erosion by 2100 due to sea-level rise and other factors.

California's stunning coastline, famous for its pristine beaches and breathtaking vistas, faces an uncertain future as new research estimates that between 24 to 75 percent of California's beaches could become completely eroded by the end of the century with no interventions. With a sea-level rise of one meter (~3 feet)—considered likely by 2100 by the State of California—a quarter of the state's coastline would see significant erosion where the beach would be completely drowned. A more extreme, low-probability rise of 3.0 meters could lead to the loss of up to three quarters of beaches. 

The study, A model integrating satellite-derived shoreline observations for predicting fine-scale shoreline response to waves and sea-level rise across large coastal regions, applies advanced technology to estimate shoreline change, highlighting the potential impact of sea-level rise and other local processes on California's coastal landscapes. Led by a team of scientists from the USGS Pacific Coastal and Marine Science Center and the University of South Wales, Sydney, the study aims to address the lack of comprehensive monitoring data for California's extensive coastline.  

The researchers utilized observations of historical shoreline positions derived from satellite imagery instead of relying solely on traditional shoreline survey data, such as on-site GPS measurements or Lidar (Light Detection and Ranging) from aircraft. By combining these observations with data on waves, sea-level rise scenarios ranging from 0.25 to 3.0 meters, and other local factors, the team developed a sophisticated model to simulate shoreline change along the entire 1,760-kilometer coastline. 

USGS Research Oceanographer Sean Vitousek, lead author of the study, emphasized the significance of this study in providing a more comprehensive understanding of coastal erosion and accretion trends. "By incorporating historical shoreline data obtained from satellite images, we were able to overcome the limitations of traditional survey methods and obtain a broader perspective on the past, present, and future of California's coastline," said Vitousek. While traditional methods might yield only around five shoreline measurements for a beach, satellite imagery dating back to 1984 can yield hundreds.

Satellite-derived shoreline imagery showing projected shoreline positions given different sea-level rise scenarios
Shoreline modeling predictions for ∼1,760 km of coastline in California produced by the current CoSMoS-COAST model, from the study A Model Integrating Satellite-Derived Shoreline Observations for Predicting Fine-Scale Shoreline Response to Waves and Sea-Level Rise Across Large Coastal Regions. The predictions represent the shoreline position in 2100 with 1.0 m of sea level rise. The yellow bands represent the projected shoreline position and (parametric) uncertainty, and the orange/red bands represent the potential storm-driven erosion uncertainty.

The findings of this research have significant implications for coastal communities, ecosystems, and industries that rely on California's beaches. The potential loss of such a significant percentage of beaches would not only impact tourism and recreation but also threaten coastal infrastructure and habitats. Further, beaches are the first line of defense against coastal flooding. 

"Understanding the potential impact of sea-level rise and other processes on California’s beaches allows policymakers, land-use planners, and communities to develop effective strategies for coastal management and climate adaptation,” said USGS Research Geologist Patrick Barnard, a co-author of the study. “This research underscores the need for proactive measures to mitigate the effects of rising sea levels to protect our valuable coastal resources.”

While the new study provides the first-ever results at this scale and resolution for Northern California, it serves as an update to previous shoreline change projections led by Vitousek for Central and Southern California. The previous results have been used extensively for coastal vulnerability assessments and adaptation planning, and are currently included in the Our Coast Our Future web tool.

The USGS team is developing an outreach and engagement strategy for the Fall 2023, in partnership with the California Coastal Commission, to provide guidance and technical support to existing end-users as they transition to using the new results. This will include the phased integration of the new shoreline change results into the Our Coast Our Future and Hazard Exposure and Reporting Analytics (HERA) web tools, a Frequently Asked Questions (FAQ) document that highlights the key differences and implications of the new satellite-based modeling approach, as well as a webinar for existing end-users (Central and Southern California) and potential new end-users (Northern California).

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