  Understanding flood probabilities is essential to making sound decisions
about flood-risk management. Many people rely on flood probability maps to
inform decisions about purchasing flood insurance, buying or selling
real-estate, flood-proofing a house, or managing floodplain development.
Current flood probability maps typically use flood zones (for example the 1 in
100 or 1 in 500-year flood zones) to communicate flooding probabilities.
However, this choice of communication format can miss important details and
lead to biased risk assessments. Here we develop, test, and demonstrate the
FLOod Probability Interpolation Tool (FLOPIT). FLOPIT interpolates flood
probabilities between water surface elevation to produce continuous
flood-probability maps. We show that FLOPIT can be relatively easily applied to
existing datasets used to create flood zones. Using publicly available data
from the Federal Emergency Management Agency (FEMA) flood risk databases as
well as state and national datasets, we produce continuous flood-probability
maps at three example locations in the United States: Houston (TX), Muncy (PA),
and Selinsgrove (PA). We find that the discrete flood zones generally
communicate substantially lower flood probabilities than the continuous
estimates.
