Historically redlined neighborhoods in 202 American cities experience higher flood exposure than higher-graded neighborhoods. People often assume flood risk depends purely on proximity to rivers or coastlines, but severe flooding strikes these zones regardless of their distance from open water. Floodwaters pool and swamp streets because aging, inadequate drainage infrastructure fails to divert heavy rainfall away from homes.
Intense rainstorms dump water across urban surfaces that cannot absorb the volume. Like a blocked sink, deficient storm drains allow rising water to back up directly into roadways and basements. The pooling runoff spreads across low-lying neighborhood blocks and traps residents inside their properties. This excess water accumulates most severely in regions with historically dense industrial labor zones and older public works.
Researchers analyzed flood exposure across 202 American cities evaluated for lending risk by the Home Owners’ Loan Corporation. The team combined high-resolution flood modeling with dasymetric population mapping to track where populations live relative to flood zones. They found that 6.4 percent of D-graded residents face 100-year floods, whereas only 5.9 percent of A-graded residents face rarer 1000-year floods.
City planners can now direct stormwater infrastructure investments toward historically redlined zones to reduce flood disparities. Targeting upgrades in the Midwest and Mid-Atlantic regions addresses the widest historical exposure gaps identified by the models.