Flood risk inequities in Houston, Texas: Novel insights based on dasymetric mapping and state-of-the-art flood modeling

Authors: Aaron Flores*, University of Utah, Timothy W Collins, Department of Geography, University of Utah, Sara E Grineski, Department of Sociology, University of Utah, Christopher C Sampson, Fathom
Topics: Hazards, Risks, and Disasters, Environmental Justice, Hazards and Vulnerability
Keywords: flood risk, inequity, environmental justice, Houston, dasymetric mapping
Session Type: Virtual Paper
Day: 4/8/2021
Start / End Time: 11:10 AM / 12:25 PM
Room: Virtual 7
Presentation File: No File Uploaded


In the United States (US), flood risk is delineated by the Federal Emergency Management Agency (FEMA). FEMA-delineated flood zones are used to define flood risks, regulate flood insurance premiums, and inform flood management. Studies have not consistently observed social disparities in FEMA-delineated 100-year flood risks, yet studies of actual flood events (e.g., Hurricanes Katrina and Harvey) indicate that socially disadvantaged groups tend to experience greater residential flooding than privileged groups. This suggests that current knowledge of disparities in flood risks may inaccurately reflect actual inequities in exposure to flood hazards in the US. This study utilizes spatial data from a state-of-the-art flood hazard model developed by Fathom-Global and sociodemographic data on census tracts from the American Community Survey (ACS) to examine social inequities in 100-year flood risk in the Houston metropolitan statistical area (MSA), where extensive flood damage induced by hurricanes and extreme precipitation events regularly occurs. We employ dasymetric mapping techniques to accurately represent each tract’s population and conduct parallel analyses of flood risk inequities using 100-year flood zones delineated by Fathom-Global versus FEMA, in order to test for flood risk inequities and compare results between the two flood risk models. We also examine social inequities in ‘federally-overlooked’ 100-year flood risk by analyzing areas within Fathom-Global delineated 100-year flood zones but outside of FEMA-delineated 100-year flood zones. Findings offer novel and practically relevant insights on flood risk inequities in the Houston MSA.

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