Delineating the Reality of Flood Risk and Loss in Southeast Texas

Abstract

Although the 100-year floodplain is the traditional indicator of risk from flooding and a catalyst for mitigation decisions in the United States, increasing evidence indicates that this boundary is not sufficient in representing actual economic losses caused by floods. Although studies have demonstrated that up to 50% of losses occur outside floodplain boundaries, as of this writing it is believed little or no research has been conducted on the precise spatial characteristics of these losses or offers an alternative approach for depicting flood exposure at the local level. This perceived lack of inquiry is addressed by spatially examining the pattern of insured flood loss within the Clear Creek watershed near Houston as a first step in better understanding the relationship between floodplain boundaries and actual loss. First, property damage claims are mapped under the National Flood Insurance Program over an 11-year period from 1999 to 2009 and then these points of loss are analyzed in relation to the 100-year floodplain and other landscape-level proximity variables. Second, spatial cluster analysis of damage points is used to generate an alternative delineation for representing flood risk and associated loss across the landscape. Results provide important insights into the spatial reality of flood damage across coastal watersheds that can help local decision makers and homeowners better understand the risk of property damage from flooding events.