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Large and inequitable flood risks in Los Angeles, California


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.

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Data availability

The parcel-level dataset developed for this study is available through the Dryad and digital repository accessible at

Code availability

Codes used for exposure and equity analysis are available through the Zenodo digital repository accessible at 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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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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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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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).

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