The impact of increasing flood frequency on flood inundation: a case study of the Little River in Florida

Abstract

Floods are considered one of the most devastating natural hazards and are projected to increase in frequency and magnitude in many places around the world, one of them being Florida. Understanding the potential changes of flood hazards due to climate change is of paramount importance for developing effective flood mitigation procedures and resilient infrastructures. In this work, changes in flood inundation characteristics (flood depth and extent) in response to changes in future flood magnitudes are estimated and analyzed for the Little River basin in northwest Florida. HEC-RAS hydraulic model is set up and validated against observations for the flood event during hurricane Sally and is used for flood scenarios of increasing magnitude of today’s 100-year flood. Findings indicate that for the range of change in flood magnitude examined (5-30%) the corresponding change in flood inundation characteristics is linear and with a rate of change (increase) that depends on the inundation characteristics. For 5% change in flood magnitude, the corresponding change in flood depth and flood extent is found 3 and 1% respectively. Sensitivity analysis revealed that flood inundation results are sensitive primarily to roughness coefficient, which must be chosen after thorough model calibration, while the results did not vary significantly for model grid size between 5 and 50m resolution. Based on the findings for the area examined, climate change impact on flood risk can have important socioeconomic implications and therefore careful assessment of future flood risk is recommended for other flood-prone areas in Florida.