Research ArticleATMOSPHERIC SCIENCE

Atmospheric rivers drive flood damages in the western United States

See allHide authors and affiliations

Science Advances  04 Dec 2019:
Vol. 5, no. 12, eaax4631
DOI: 10.1126/sciadv.aax4631
  • Fig. 1 An AR on 9 January 1995 caused substantial damages on the west coast of the United States.

    (A) 4 National Center of Environmental Prediction–National Center for Atmospheric Research (NCEP-NCAR) precipitable water preceded peak damages in California. (B) Maximum coastal IVT (given here over the entire west coast), generated peak precipitation over Sonoma County (see Materials and Methods), streamflow at the U.S. Geological Survey Guerneville gauge, and total insured losses in Sonoma County. (C) Flood insurance claims along the lower reach of the Russian River in Sonoma County are marked as red dots; the 100-year flood plain is indicated in blue.

  • Fig. 2 From 1978 to 2017, ARs accounted for 84.2% of all insured flood losses in the 11 western states across all seasons.

    In many areas in coastal northern California and the Pacific Northwest, ARs accounted for over 95% of insured flood losses.

  • Fig. 3 Flood damages increase exponentially with AR category.

    (A) The Ralph et al. AR scale (20) classifies ARs into five categories depending on IVT and duration. For example, an AR with a peak IVT of 800 kg m−1 s−1 and a duration of 78 hours is classified as a category 4 or extreme AR. (B) NDJFM flood damages increase exponentially with AR category: Vertical scale is logarithmic; black bars are medians; boxes are 25th and 75th percentiles, and whiskers are 5th and 95th percentiles; dots are extrema; numbers in parentheses are the number of NDJFM events in each category. Note that the total number of ARs in the Gershunov AR catalog (1603) is greater than the number of ARs over the sample period using the Ralph et al. AR scale (1134), which classifies events with a duration of less than 24 hours as non-ARs.

  • Table 1 Most damaging atmospheric rivers 1978–2017.

    Start dateInitial landfall
    region
    Initial landfall
    latitude
    AR categoryPeak IVT
    (kg m−1 s−1)
    ClaimsInsured losses
    ($m)
    Total damages
    ($b)
    4 January 1995S. CA32.5°N49664725125.83.7
    29 December
    2005
    N. CA40°N48252554117.63.5
    29 December 1996Central CA35°N512603407104.63.1
    5 February 1996N. OR45°N3729269599.33.0
    2 December 2007N. OR45°N51258144783.92.5
    15 February 1986WA47.5°N4870204866.62.0
    7 March 1995S. OR42.5°N4928234358.71.8
    5 January 2009S. OR42.5°N4831163653.91.6
    1 February 1998Bay Area37.5°N4795241746.81.4
    1 November 2006N. CA40°N51041118438.71.2
    25 January 1983Bay Area37.5°N51013154534.91.0
    25 February 1983Bay Area37.5°N3658183230.00.9
    12 February 1980Baja CA30°N3721205928.50.9
    3 January 1982N. CA40°N3525142228.10.8
    11 February 1986N. CA40°N490484823.90.7
    21 November
    1990
    WA47.5°N494393923.30.7
  • Table 2 Proportion of losses caused by ARs in top counties.

    CountyAR proportion of
    insured losses
    ClaimsInsured losses ($m)Total damages ($b)AR damages ($b)
    Sonoma, CA0.9986650172.05.25.2
    Los Angeles, CA0.8468280106.13.22.7
    Lewis, WA0.9891979101.43.03.0
    Marin, CA0.987315273.22.22.2
    King, WA0.970291569.02.12.0
    Sacramento, CA0.977360956.91.71.7
    Snohomish, WA0.903181843.71.31.2
    Monterey, CA0.989125343.51.31.3
    Napa, CA0.997133143.21.31.3
    Washoe, NV0.99872042.41.31.3
    Maricopa, AZ0.628236833.71.00.6
    Santa Clara, CA0.971155733.41.01.0
    Clackamas, OR0.97073031.50.90.9
    San Diego, CA0.912194530.70.90.8
    Orange, CA0.899361929.30.90.8
    Pierce, WA0.97493428.40.90.9
    Riverside, CA0.624161927.90.80.5
    Cowlitz, WA0.59670926.60.80.5
    Placer, CA0.99059826.50.80.8
    Columbia, OR0.99841424.70.70.7
  • Table 3 Summary statistics of damages by atmospheric river category, November to March, in millions of dollars.

    Damages under $50,000 are rounded down to $0.

    AR CATNumber of
    events
    Minimum
    ($m)
    5% ($m)25% ($m)Median ($m)75% ($m)95% ($m)Maximum
    ($m)
    CAT 11300000.1124208
    CAT 21680000.3448844
    CAT 3201000.1210942930
    CAT 49900.13198514243773
    CAT 5113524259110228213126
    All ARs6090002101973773

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/12/eaax4631/DC1

    Supplementary Text

    Fig. S1. Coastal grid cells.

    Fig. S2. NFIP payments versus NWS damages.

    Fig. S3. Distribution and time course of insured losses.

    Fig. S4. Spatial footprints of ARs.

    Fig. S5. Seasonality of insured losses.

    Fig. S6. Days with over $1 million in insured losses.

    Table S1. Damages by AR category by month, in millions of dollars.

    Table S2. Effect of antecedent ARs on mean flood damages by AR event.

    Table S3. Average claims and insured losses per latitude-day by AR intensity (quartiles).

    Table S4. Daily average insured losses by latitude band by AR intensity.

    Data S1.

    Reference (41)

  • Supplementary Materials

    The PDFset includes:

    • Supplementary Text
    • Fig. S1. Coastal grid cells.
    • Fig. S2. NFIP payments versus NWS damages.
    • Fig. S3. Distribution and time course of insured losses.
    • Fig. S4. Spatial footprints of ARs.
    • Fig. S5. Seasonality of insured losses.
    • Fig. S6. Days with over $1 million in insured losses.
    • Table S1. Damages by AR category by month, in millions of dollars.
    • Table S2. Effect of antecedent ARs on mean flood damages by AR event.
    • Table S3. Average claims and insured losses per latitude-day by AR intensity (quartiles).
    • Table S4. Daily average insured losses by latitude band by AR intensity.
    • Reference (41)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article