Homeowner Flood Risk and Risk Reduction from Home Elevation between the Limits of the 100- and 500-year Floodplains

Carol Friedland, Kleinpeter, Shelly, Mostafiz, Rubayet Bin

Recent catastrophic events and studies regarding projected trends under environmental change scenarios reveal that the area outside the presently designated special flood hazard area (SFHA) is subjected to rapidly increasing flood risk. Flood risk outside the SFHA is often underestimated because of minimal flood-related insurance requirements and regulations and sparse flood depth data. Therefore, this study proposes a systematic approach to predict flood risk for a single-family home using average annual loss (AAL) in the shaded X Zone – the area immediately outside the SFHA (i.e., the 500-year floodplain), which lies between the limits of the 1.0- and 0.2-percent annual flood probability.

The derivation of synthetic flood hazard parameters enables the estimation of flood risk values in the shaded X Zone. Our analysis shows that the median AAL for all four types of single-family homes (one- and two-plus-story, each without and with basement) in the shaded X Zone falls between 0.10 to 0.78 percent of replacement cost value. Also, it shows that the median value of AAL reduction falls between 0.06 and 0.23 percent of replacement cost value when elevating by an additional 1 and 4 feet, respectively, above the initial first- floor height.

To validate our findings, we compare the AALs for case study subsets in Jefferson Parish, Louisiana and Santa Clarita, California generated through spatial interpolation-estimated flood parameters with those obtained using synthetic flood parameters. The AAL results from the spatial interpolation approach fall within the range of AALs derived using synthetic flood parameters.

Case study areas in Santa Clarita, California, and Jefferson Parish, Louisiana, highlighting the homes situated in the Special Flood Hazard Area (SFHA) and shaded X Zone.

This study provides an important first step for predicting and enhancing community understanding of the flood risk in the shaded X Zone and provides a clearer perception of the advantages of applying mitigation strategies in those areas. The methodology and results generated in this paper will benefit homeowners, builders, developers, community planners, and other partners in the process of enhancing resilience to the flood hazard via risk-informed construction techniques.

To see the results in detail and read more about our peer-reviewed publication on this research click on the link below.

Al Assi, A., Mostafiz, R. B., Friedland, C. J., Rohli, R. V., Rahim, M. A. (2023c). Homeowner flood risk and risk reduction from home elevation between the 100-and 500-year floodplains. Frontiers in Earth Science, 11, Art No. 10512378. https://doi.org/10.3389/feart.2023.1051546

7/10/2023 3:11:47 PM
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