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Large and inequitable flood risks in Los Angeles, California

Nature Sustainability volume 6, pages 47–57 (2023)Cite this article

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Abstract

Flood risks in the United States have historically been underestimated, particularly with respect to human well-being and within low-wealth and marginalized communities. Here, we characterize a fuller range of risks in Los Angeles, California, using a quantitative framework that intersects flood hazards from rainfall, streamflow and storm tides with measures of exposure and vulnerability including ethnicity, race and socioeconomic disadvantage. We find that between 197,000 and 874,000 people (median 425,000) and between US$36 billion and US$108 billion in property (median US$56 billion) are exposed to flooding greater than 30 cm within the 100-year flood zone, risk levels far above federally defined floodplains and similar to the most damaging hurricanes in US history. These risks are disproportionately higher for non-Hispanic Black and disadvantaged populations, burdening communities that may have greater challenges recovering and reinforcing socioeconomic inequities. Our framework creates opportunities for transparently and equitably reducing flood risks in urban areas.

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Fig. 1: 100-year compound flood hazard in Los Angeles.
Fig. 2: Flood exposure by race and ethnicity.
Fig. 3: Flood exposure by socioeconomic indicators.
Fig. 4: Prioritization of risk reduction resources.
Fig. 5: Uncertainty in the 100-year return period flood hazard area.

Data availability

The parcel-level dataset developed for this study is available through the Dryad and digital repository accessible at https://doi.org/10.7280/D1RH7Z.

Code availability

Codes used for exposure and equity analysis are available through the Zenodo digital repository accessible at https://doi.org/10.7280/D1RH7Z. Custom codes in Fortran, Matlab, Python and R used for data preparation, flood simulation and postprocessing are available upon written request from the authors.

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Acknowledgements

We express our thanks to the County of Los Angeles and the County of Orange for assistance with access to data used for this study. We thank S. Grant for valuable discussion and A. Jong-Levinger for assistance preparing model data. We also acknowledge high-performance computing support from the NCAR-Wyoming Supercomputing Center provided by the National Science Foundation and the State of Wyoming and supported by NCAR’s Computational and Information Systems Laboratory. Figures with maps were created using ArcGIS software by Esri. This work was supported by grants from the National Science Foundation (Coastlines and People grant no. ICER-1940171, INFEWS grant no. EAR-1639318 and grant no. HDBE-2031535), the NOAA Effects of Sea Level Rise Program (grant no. NA16NOS4780206) and the Ridge to Reef NSF Research Traineeship (grant no. DGE-1735040).

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Authors and Affiliations

  1. Department of Civil and Environmental Engineering, University of California, Irvine, CA, USA

    Brett F. Sanders, Jochen E. Schubert, Daniel T. Kahl, Amir AghaKouchak & Steven J. Davis

  2. Department of Urban Planning and Public Policy, University of California, Irvine, CA, USA

    Brett F. Sanders, Richard A. Matthew & Nicola Ulibarri

  3. UCI Blum Center for Poverty Alleviation, University of California, Irvine, CA, USA

    Brett F. Sanders, Jochen E. Schubert, Amir AghaKouchak, Richard A. Matthew, Nicola Ulibarri & Steven J. Davis

  4. Department of Environmental Science and Policy, Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami, Miami, FL, USA

    Katharine J. Mach

  5. Leonard and Jayne Abess Center for Ecosystem Science and Policy, University of Miami, Coral Gables, FL, USA

    Katharine J. Mach

  6. School of Public Policy, University of California, Riverside, CA, USA

    David Brady

  7. Blum Initiative on Global and Regional Poverty, University of California, Riverside, CA, USA

    David Brady

  8. Department of Earth System Science, University of California, Irvine, CA, USA

    Amir AghaKouchak & Steven J. Davis

  9. Department of Political Science, University of California, San Diego, CA, USA

    Fonna Forman

  10. Center for Global Justice, University of California, San Diego, CA, USA

    Fonna Forman

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Contributions

The project concept was conceived by A.A., D.B., S.J.D., F.F., K.J.M., R.A.M., B.F.S., J.E.S. and N.U. who also contributed to funding acquisition. The methodology was developed and validated by D.B., S.J.D., D.K., B.F.S. and J.E.S. The investigation and formal analysis was by S.J.D., K.J.M., B.F.S. and J.E.S. The original draft was prepared by D.B., S.J.D., K.J.M, B.F.S. and J.E.S. All authors contributed to review and editing.

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Correspondence to Brett F. Sanders.

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Nature Sustainability thanks Paul Bates, Oronde Drakes and Mathis Messager for their contribution to the peer review of this work.

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Supplementary Methods, Tables 1–5 and Figs. 1–5.

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Sanders, B.F., Schubert, J.E., Kahl, D.T. et al. Large and inequitable flood risks in Los Angeles, California. Nat Sustain 6, 47–57 (2023). https://doi.org/10.1038/s41893-022-00977-7

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