Nederhoff et al. (2026) Beyond the 100-year flood: probabilistic flood hazard assessment for King and Pierce Counties under future climate scenarios

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2026
• Date: 2026-07-13
• Authors: Kees Nederhoff, Kai A. Parker, Eric E. Grossman
• DOI: 10.5194/nhess-26-3231-2026

Research Groups

• Deltares USA
• Washington State Department of Ecology
• U.S. Geological Survey, Pacific Coastal and Marine Science Center

Short Summary

This study presents a high-resolution flood hazard mapping approach for King and Pierce Counties in Washington State using the SFINCS model to facilitate a Continuous Flood Response Modeling (CFRM) framework. The research predicts flood areas for return periods of 1 to 100 years and computes the Expected Annual Flooded Area (EAFA) as a probability-weighted indicator of flood exposure.

Objective

• Assess compound flood hazard in King and Pierce Counties, Washington, using the Continuous Flood Response Modeling (CFRM) framework.
• Evaluate the impact of sea level rise on flooding in the study area.

Study Configuration

• Spatial Scale: High-resolution model domains were constructed for King and Pierce Counties at a 50 m resolution, covering an average area of 3000 km^2.
• Temporal Scale: The reanalysis period spanned water years 1941 through 2022, while future climate projections were simulated for the period 1950 to 2050.

Methodology and Data

• Models used: SFINCS (Super-Fast INundation of CoastS) model, Delft3D FM, SWAN, wflow hydrological modeling framework.
• Data sources: Coastal National Elevation Database (CoNED), NOAA tide gauge stations, USGS streamgages, ERA5 reanalysis data, CMIP6 models.

Main Results

• The study found that the primary driver of increasing flood extent is sea level rise, with an increase of 80% to 360% with 1 m SLR.
• Climate change drivers, such as changes to storm patterns, reduce hazards minimally.
• A threshold was identified where there is a substantial increase in the area of land that is flooded when sea levels rise above 100-150 cm.
• The study also found that simple deterministic flood maps may underrepresent flood hazard by approximately 0.5 m if not all contributing factors are considered.

Contributions

• This study advances flood risk science by introducing a high-resolution, probabilistic framework that integrates coastal and fluvial dynamics through continuous modeling.
• The study provides actionable insights for more accurate, climate-informed flood risk assessment and spatial planning in vulnerable coastal regions.

Funding

• Not specified.

Citation

@article{Nederhoff2026Beyond,
  author = {Nederhoff, Kees and Parker, Kai A. and Grossman, Eric E.},
  title = {Beyond the 100-year flood: probabilistic flood hazard assessment for King and Pierce Counties under future climate scenarios},
  journal = {Natural hazards and earth system sciences},
  year = {2026},
  doi = {10.5194/nhess-26-3231-2026},
  url = {https://doi.org/10.5194/nhess-26-3231-2026}
}