Examining the 100-year floodplain as a metric of risk, loss, and household adjustment.

An understudied, but central aspect in understanding flood impacts is the way we conceptualize, identify, and delineate risk. The 100-year floodplain is the longstanding metric in the United States for determining and acting upon the possibility of an area being inundated. This spatial delineation guides local planning and development decisions, triggers insurance purchases and other household adjustments, and serves as the fundamental indicator for whether it is safe to build a structure on a particular site. However, increasing evidence suggests that the 100-year floodplain is neither accurate nor sufficient in guiding communities and household decisions to mitigate the adverse economic impacts of floods. In this perspective, we examine the effectiveness of the 100-year floodplain as an appropriate marker of risk. First, we review existing studies on location and flood damage. Next, we apply these concepts to repetitive flood losses data in Harris County, Texas. We conclude that the apparent inability of the floodplain designation to effectively capture the likelihood of property damage and potential loss of human life in coastal areas has left potentially millions of property owners unaware of the flood risk and unprepared to mitigate their adverse impacts. Relying on traditional 100-year floodplain boundaries, local decision makers are hampered in their ability to ensure community development occurs in a resilient manner. Finally, we set forth an agenda for future research to better capture the conditions associated with flood risk and account for the large percentage of damage outside the designated floodplain.