Buried but not dead: The impact of stream and wetland loss on flood risk in redlined neighborhoods

The United States government sponsored the Home Owners’ Loan Corporation (HOLC) in the 1930s to assess and grade neighborhoods based on perceived financial risk. The grades were influenced by the presence of minority racial groups, immigrants, and residents with lower socioeconomic statuses and, even though the practice was eventually outlawed, the impact on low income and underrepresented minorities is still prevalent today. This study was designed to assess spatial patterns and intensity of flood risk to (a) HOLC grade, (b) proximity to coastal zones, (c) intensity of vegetative cover, and (d) relationship to buried (ghost) streams and wetlands to determine which variable has the most impact on flood risk. Flood risk data, acquired from First Street Foundation’s Flood Factor dataset, was summarized by HOLC grade, and ghost streams and wetlands were digitized from historical maps and aggregated by HOLC grade. The results show flood risk is higher in C and D graded neighborhoods, compared to A and B. Regardless of HOLC grade, neighborhoods near the Detroit River and Lake St. Claire have 10 times higher flood risk than inland neighborhoods. Interestingly, B-graded neighborhoods exhibit minimal impact from buried rivers and wetlands, but that risk increases substantially if there is a history of stream or wetland burial within a D graded neighborhood. Flood risk is disproportionately distributed, caused in part by outlawed, racist housing policies. Understanding where risk is highest can help identify optimum locations for adaptation measures to minimize flood damage in these neighborhoods.