Loss prevention and distribution must begin well before a flood event at multiple levels. However, the benchmarks and terminology we use to manage and communicate flood risk may be working against this goal. U.S. flood policy is based upon a flood with a one percent chance of occurring in any year. Commonly called the "hundred year flood," it has been upheld as a policy criterion, but many have questioned the effectiveness of hundred year flood terminology in public communication. This research examined public perceptions of the hundred year flood and evaluated the comparative effectiveness of this term and two other methods used to frame the benchmark flood: a flood with a one percent chance of occurring in any year and a flood with a 26 percent chance of occurring in thirty years. This research also explored how flooding and flood risk messages fit into the larger context of people's lives by modeling the relationships between flood related understanding, attitude and behavior and the situational and cognitive contexts in which these factors are embedded. The final goal was to come up with locally based suggestions for improving flood risk communication. Data were collected in the Towns of Union and Vestal, New York. Participants were adult residents of single family homes living in one of two FEMA designated floodplains. Face to face surveys and focus groups were used to gather information on respondents' flood experience and loss mitigation activities; general perception of flood risk and cause; flood information infrastructure; perceptions associated with specific flood risk descriptions; and basic demographic data. Focus groups were also asked to suggest improvements to flood risk communication. Results indicated that experience was the most influential factor in perception and behavior. Additionally, there was little evidence that understanding led to "appropriate" behavior. The 26 percent chance description was the most effective when both understanding and persuasion were included, but interpretations of probabilistic flood risk messages were highly individualized. Finally, regulatory practice likely influences attitude and behavior and may emphasize the likelihood of a particular flood at the expense of the possibility of flooding in general.

In response to the rising costs of floods, the United States has adopted sophisticated programs to mitigate the loss of life and property. However, the efficient implementation of certain aspects of flood policy has taken precedence over effective communication. The scope of the National Flood Insurance Program and the efficient coding of "the 100 year flood" have led to a pervasive use of the term in both formal and informal risk communication. When officials began consciously communicating flood policy to the public, they assumed a narrow "engineering" model and did not fully anticipate the influence of informal communication on the perception of flood risk. The effectiveness of the "100 year flood" as a means to change attitudes or motivate behaviors was not assessed. Nor was its utility in increasing public understanding of flood risk. New explanatory methods have been introduced, but they, too, have yet to be tested. This project evaluated the effectiveness of four methods commonly used to communicate the risk associated with policy's benchmark flood. These include: a 100 year flood; a flood with a 1 percent chance of occurring in any year; a flood with a 26 percent chance of occurring in 30 years; and a flood risk map available through Project Impact. Data were collected using a structured face to face questionnaire survey of residents living in Wimberley, Texas. Respondents included individuals who lived inside the boundaries of official flood plains, as well as those who did not. Comparable questions regarding uncertainty, perceived need for protection, and levels of concern were asked using each of the four methods of description. Qualitative observations were made during both the interviews and the collection of secondary data. Results showed a significant disjuncture of understanding and persuasion with each method; potentially serious problems with the 26 percent chance method; and a preference for concrete references in describing risk. It is recommended that use of the 26 percent chance method be discontinued. Both the 100 year flood and the map performed better than expected; these descriptions are recommended with reservations in lieu of more contextually appropriate methods of communication and policy formation.