Framing the Challenge of Urban Flooding in the United States (2019) / Chapter Skim
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3 Magnitude of Urban Flooding
3 Magnitude of Urban Flooding
Pages 29-50
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From page 29... ...
To address this gap, the committee drew on published estimates of flood losses in the case study areas and also analyzed federal flood loss data. This chapter presents results from two typical methods for estimating the magnitude of urban flooding in the case study areas: (1)
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From page 30... ...
Major Flood Events Historical records indicate where, how often, and how damaging major floods have been. Major floods were responsible for most of the past flood losses in the United States.
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For the most recent decade of the data (2005–2014) , the annual average freshwater flood loss was $9.1 billion with 71 fatalities.
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Summary of Major Flood Events Data Sets The FEMA and NOAA data sets discussed above suggest that losses from large flood events are substantial and are increasing over time. The NOAA estimates show that annual losses associated with direct damage from major flood events across the United States range from $7 billion to $9 billion on average, and that associated fatalities range from 70 to 96 fatalities on average.
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grants zip code Funds large hazard mitigation projects intended to help communities reduce their risk from future disasters.
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SHELDUS 1960–2016 County Freshwater flood-related (derived from Injuries and fatalities NOAA) Direct damage to property and crops Insured crop losses (1989-2016)
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Note that differences in which years' historical estimates are calculated can yield different results. For example, if the data range included 2017 (the year Hurricane Harvey hit)
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Arizona $11 The decadal, county-level data in Table 3.3 can be converted into an annual per capita cost for the four case study areas, as shown in Table 3.4. The per capita data vary substantially across these areas, from $0.3/year in Maricopa County to $2.6/year in Baltimore County to $35.2/year in Cook County to $65.2/year in Harris County.
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From page 37... ...
Two of the case study areas appear in this list, with Houston receiving substantial assistance in buyouts and NFIP insurance payouts, and Chicago receiving substantial IA awards. TABLE 3.5 Metropolitan Zip Codes with the Highest FEMA Assistance ($ millions)
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From page 38... ...
and along Galveston Bay in 2008 with a large storm surge. If the time period were extended to 2017 to include Hurricane Harvey, the losses would be located further inland and to the west of the city.
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for Houston-Galveston zip codes. SOURCE: Center for Texas Beaches and Shores, Texas A&M University, Galveston Campus.
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Furthermore, some Presidential Major Disaster Declarations do not include an IA designation (Lindsay and Reese, 2018)
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with the highest total direct property flood losses in the SHELDUS database from 1960 to 2016 are listed in Table 3.7. None of the case study areas appear in the top 10, but they are included at the end for comparison.
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From page 42... ...
These data illustrate the inherent flood risk concentrated in heavily populated coastal counties along the Gulf Coast and in Florida, which include cities such as Houston, Gulfport, and Miami. The SHELDUS data, which emphasize freshwater flooding, highlight a number of inland urban areas with substantial flood losses, including Cedar Rapids, Grand Forks, Memphis, Detroit, and Nashville, each of which had total flood losses exceeding $2 billion from 1960 to 2016.
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From page 43... ...
The aqueduct tool assumption is that up to 5 years of flood protection is in place in each city. TABLE 3.8 World Resources Institute Aqueduct Global Flood Analyzer Estimates of Annualized Direct Damage to Assets and Population Due to Riverine Flooding in Urban Areasa Direct Urban Damage ($ billions)
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(2013) used a port city flood risk assessment methodology to assess average annual flood losses in 136 coastal cities around the world.
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(2018) model identifies more extensive floodplain than the FEMA riverine flood studies.
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(2018) riverine and pluvial flood model (bottom, red)
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From page 47... ...
In the meantime, FEMA is licensing AIR and RMS inland flood and storm surge models to analyze loss potential for the NFIP.10 Summary of Flood Risk Assessments in Urban Areas Flood risk assessments offer a more comprehensive, but still incomplete, picture of urban flooding than historical estimates because they include a wider range of flood probabilities and additional socioeconomic factors (e.g., effect on GDP)
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From page 48... ...
Fatalities/Injuries IA Awards Average Annual Population Case Study Area Loss ($ millions) Exposurec 1960–2016 2004–2014 1960–2016 2004–2014 Baltimore Metropolitan Area 76a 120,000 82 11/26 182 Baltimore County 12 38 5/2 0 48 Chicago Metropolitan Area 3,300b 945,000 1,241 26/6 211,565 Cook County 659 1,827 15/0 182,388 Houston Metropolitan Area 3,300b 1,178,000 549 63/5 155,960 Harris County 272 2,667 40/3 83,537
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From page 49... ...
. b From World Resources Institute (see Table 3.8)
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From page 50... ...
, an average of $3.3 billion in direct property damages can be expected in these metropolitan areas. If accurate, these assessments are a lower bound of urban flood losses, given that they omit losses from pluvial flooding.
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