A once-in-one-hundred-year event? A survey assessing deviation between perceived and actual understanding of flood risk terminology

The US National Flood Insurance Program maps and classifies flood risk based on observed data for the frequency of flood events, using terms such as ‘100-year flood’ and ‘500-year flood.’ The purpose of these classifications is to convey information about the likelihood of a flood event to property owners and to inform the decision or mandate to purchase flood insurance. The flooding that followed Hurricane Harvey in 2017 brought heightened use of 100-year-flood terminology in the media. Often, the term was incorrectly used, misrepresenting the risk that is intended to be conveyed by the technical term. Misuse of flood terminology and related misperception of risk has important implications for society, including over- or under-insuring property owners and inadequate individual and collective preparedness. This paper presents the findings of a survey conducted to gauge understanding of Federal Emergency Management Agency flood risk terminology and to examine links between estimating flood risk and proximity to flooding, knowledge of independent probabilities, and demographics. We found that the driving force behind correctly interpreting technical flood terminology was understanding of independent probabilities, while education and recent exposure or proximity to a severe flood event did not have a statistically significant influence.