Homeowner Flood Risk and Risk Reduction from Home Elevation between the
100- and 500-year Floodplains
Abstract
Floods inflict significant damage even outside the 100-year floodplain.
Thus, restricting flood risk analysis to the 100-year floodplain
(special flood hazard area (SFHA) in the U.S.A.) is misleading. Flood
risk outside the SFHA is often underestimated because of minimal
flood-related insurance requirements and regulations and sparse flood
depth data. 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 1.0- and 0.2-percent annual
flood probability. To further inform flood mitigation strategy, annual
flood risk reduction with additional elevation above an initial
first-floor height () is estimated. The proposed approach generates
synthetic flood parameters, quantifies AAL for a hypothetical
slab-on–grade, single-family home with varying attributes and scenarios
above the slab-on-grade elevation, and compares flood risk for two areas
using the synthetic flood parameters vs. an existing spatial
interpolation-estimated flood parameters. Results reveal a median AAL in
the shaded X Zone of 0.13 and 0.17 percent of replacement cost value ()
for a one-story, single-family home without and with basement,
respectively, at and 500-year flood depth < 1
foot. Elevating homes one and four feet above substantially mitigates
this risk, generating savings of 0.07–0.18 and 0.09–0.23 percent of
for a one-story, single-family home without and with basement,
respectively. These results enhance understanding of flood risk and the
benefits of elevating homes above in the shaded X Zone.