Webb (2026) A Modified Atmospheric River Scale for Flood Hazards

Identification

• Journal: Open MIND
• Year: 2026
• Date: 2026-02-16
• Authors: M. J. Webb
• DOI: 10.4211/hs.cee30237618d48e8bb0d09ecff9a4a7c

Research Groups

Led by Webb, M. J. and collaborators, associated with institutions supported by the U.S. National Science Foundation.

Short Summary

This study modifies the existing Atmospheric River (AR) scale for flood hazards by incorporating antecedent soil moisture conditions, significantly improving its ability to predict peak streamflow and detect flood-generating ARs.

Objective

• To enhance the Atmospheric River (AR) scale for flood hazard assessment by integrating land surface processes, specifically antecedent moisture conditions, to improve its correspondence with peak streamflow and flood detection rates.

Study Configuration

• Spatial Scale: 142 catchments across California and central Chile, covering a geographic extent from approximately 42.1440° N to -40.3265° S latitude and -124.1170° W to -69.7690° E longitude.
• Temporal Scale: Not explicitly defined for the full dataset, but analysis covers over 70,000 Atmospheric River landfalls, utilizing event-level and daily time series data.

Methodology and Data

• Models used: Statistical analysis frameworks and R packages (e.g., glmtoolbox, relaimpo, tidyverse) were used for data processing and statistical modeling of relationships.
• Data sources: Observational data for atmospheric river characteristics (atmospheric vapor transport), antecedent soil moisture, and peak streamflow in 142 catchments across California and central Chile. Preprocessed event-level and daily time series inputs were utilized.

Main Results

• Runoff efficiency, primarily controlled by antecedent soil moisture, was identified as the dominant source of peak streamflow variability not explained by the original AR scale.
• The modified AR scale, incorporating antecedent moisture conditions, nearly doubles its correspondence with peak streamflow compared to the original scale.
• The modification increases the number of flood-generating ARs classified as hazardous by over 30%.
• The modified scale raises AR flood detection rates to 81% in California and 64% in central Chile.

Contributions

• Presents a novel, simple modification to the existing Atmospheric River scale for flood hazards by integrating antecedent moisture conditions.
• Quantitatively demonstrates the critical role of land surface conditions in enhancing the accuracy of AR hazard classification.
• Improves early-warning tools for communicating the likelihood of flood hazards associated with atmospheric rivers.
• Provides a robust framework for better predicting peak streamflow and increasing flood detection rates from AR events.

Funding

• U.S. National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP) Grant No. 1937966
• U.S. National Science Foundation (NSF) PATHWAYS International Research Experience for Students (IRES) Grant No. 1954140
• U.S. National Science Foundation (NSF) Awards 1148453, 1148090, 1664018, 1664061, 1338606, 1664119, and 1849458

Citation

@article{Webb2026Modified,
  author = {Webb, M. J.},
  title = {A Modified Atmospheric River Scale for Flood Hazards},
  journal = {Open MIND},
  year = {2026},
  doi = {10.4211/hs.cee30237618d48e8bb0d09ecff9a4a7c},
  url = {https://doi.org/10.4211/hs.cee30237618d48e8bb0d09ecff9a4a7c}
}