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Method to Transfer Flood Risk and its Application to Hurricane Harvey
  • Elizabeth Regier,
  • Joseph Naughton,
  • Walter McDonald
Elizabeth Regier
Marquette University

Corresponding Author:[email protected]

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Joseph Naughton
Marquette University
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Walter McDonald
Marquette University
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Abstract

The magnitude of Hurricane Harvey significantly altered flood frequency statistics in the region that it hit, but hurricane path projections indicate that it could have made landfall in numerous other regions along the Gulf coast. While current flood frequency methods restrict analysis to floods that occur within a specific region, due to the effects of climate change and immense size of Harvey, it is important to determine the impact that Harvey would have had if it hit other regions within its probabilistic landfall path. Therefore, this study investigates the impact that Harvey would have had on flood frequency statistics and regional flood frequency analysis if it had made landfall elsewhere. To this end, spatial rainfall data was shifted to two probabilistic landfall regions in the central and southern Gulf coast of Texas. This shifted rainfall data was then paired with synthetic unit hydrographs to create simulated Hurricane peak flows at USGS streamflow stations in each region. With few exceptions, Log Pearson III analyses of records containing simulated Harvey peak flows resulted in 2-, 5-, 10-, 25-, 50- and 100-year peak flows that were higher than Log Pearson III analyses of the original peak flow records. These increases in peak flows were larger for longer return periods – 100-year peak flows increased by an average of 63.9% in the southern coast region and 21.4% in the central coast region, while 2-year peak flows increased by an average of 9.38% in the southern coast region and 1.51% in the central coast region. These return period peak flows were then applied to regional flood frequency analysis to predict peak flows based upon drainage area and basin shape factor. Application of the equations to example watersheds in the central coast region increased estimated peak flows by up to 75%. This case study shows that moving Hurricane Harvey to different regions within its probabilistic landfall path would have a significant impact on flood frequency statistics and regional flood frequency equations. Therefore, because of the growing impact of climate change on hurricane intensity, it may be important to consider the impact that current and future extreme hurricanes like Harvey have on flood frequency statistics in other regions within their probabilistic landfall path.