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.