Distributions of Flood Risk: The Implications of Alternative Measures of Flood Risk

Abstract

Flooding imposes considerable property risk, and flood maps and flood insurance help prospective and existing property owners assess the potential risk. The US Federal Emergency Management Agency (FEMA) works with local and state officials to produce flood maps. Using these flood maps and demographic attributes, prior research has demonstrated correlations between the percent of a tract identified as disadvantaged and the percent of the tract covered by flood zones. Until recently, FEMA flood maps were the primary assessment tool for flood risk, but First Street Foundation (FSF) has developed its own flood risk tools. This paper compares these alternative flood risk measures as a percent of census tracts in the Southeastern US states and assesses models of the risk measures with demographic, housing, policy and control variables. The main results are first that the FEMA and FSF maps often reveal diverging levels of risk per tract. Second, the demographics correlating with tract-level risk differ markedly for the two risk measures. Third, the results vary considerably by state with more divergence in some states than others, and who is at risk of flooding across the states varies between the FEMA and FSF measures.