A recent NOAA-funded study by researchers at the University of Florida’s Coastal & Oceanographic Engineering Program sheds light on the factors behind the devastating flooding caused by Hurricanes Irma and Ian in Collier County, Southwest Florida. The study also demonstrates the value of high-resolution flood models and the importance of good data for building damage or loss.
Extreme weather events and rising seas are creating more frequent flooding conditions. This study shows how the team’s high-resolution flood model can estimate the flooding from historical and potential storms and predict the estimated structural losses from flooding. The team also evaluated how sea level rise and certain hurricane characteristics, such as storm speed, led to structural damage from flooding during Hurricane Ian–a Category 4 storm in 2022–and Hurricane Irma–a Category 3 storm in 2017–to inform future preparedness. Sensitivity analyses revealed that sea level rise, higher intensity, larger size, slower speed, a more perpendicular track, a northerly landfall direction, and high tide amplified Ian’s impact.
The team used a 3D vegetation-resolving surge-wave model, which maps the extent and severity of predicted flooding patterns while incorporating the beneficial contributions of vegetation, like the wave dampening effects of mangroves that reduce overall flooding. The researchers were also able to consider how accurately the new model performs by assessing their model’s output to Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP) payouts. Estimated structural losses were $126.3 million for Irma and $1.95 billion for Ian, with NFIP-insured losses within seven to 12 percent of FEMA claims. Ian’s inundation corresponded to a 100 to 10,000-year flood, while Irma’s was mostly less than 100 years, based on comparison with around 300 synthetic storm simulations. Losses were comparable to those expected from a 100-year flood as with Irma and a 3,500-year flood as with Ian.
Using the damage function of FEMA’s risk assessment tool known as FEMA-HAZUS, the estimated building loss in Collier County for NFIP-insured properties was found to be $59 million and $852 million, versus the FEMA flood loss payout data of $52.4 million and $777 million, during Irma and Ian respectively. Losses during Irma and Ian were both based on the 2022 property values which are available from Collier County.
The availability of NFIP data on flood damage claims made it possible for the modelers to verify their results of predicted flood damage costs in Collier County. In general, publicly available data from sources like FEMA can be a tool that may be used by a variety of stakeholders in hurricane-prone areas, though this data is only available on a case-by-case basis.
Two NOAA programs have supported this study including the RESTORE Science Program and Effects of Sea Level Rise (ESLR) program researchers are advancing the models behind ACUNE to produce compound flooding maps from both coastal and inland flooding. Visit the project page for additional information.
This work is authorized by the NOAA Authorization Act of 1992, Pub. L. 102-567 (Oct. 29, 1992); sec. 201(c), which authorizes appropriation for the NCCOS Competitive Research Program and the RESTORE Act (sec. 1604).