Conference Agenda

Environmental inequalities, such as unequal exposure to pollution and climate risks, persist across racial and socioeconomic groups in the United States. This paper re-examines the role of the Residential Security Maps created by the Home Owners’ Loan Corporation (HOLC) in the 1930s, which graded neighborhoods according to perceived mortgage risk and have been widely linked to long-run racial segregation and environmental disadvantage. A common view holds that these maps not only reinforced residential segregation but also directly shaped the spatial distribution of environmental hazards, including air pollution, flood risk, and extreme heat.

We evaluate this claim using a causal framework that combines machine-learning predictions of counterfactual HOLC grades in unmapped cities with a spatial difference-in-differences design. Our results confirm that the maps modestly increased racial sorting and segregation, consistent with prior work. However, we find no evidence that HOLC mapping independently affected the siting of environmental or climatic hazards. Differences in air pollution, flood risk, heat exposure, and mortality across historical grades are quantitatively similar in mapped and unmapped cities.

These findings suggest that contemporary environmental inequalities primarily reflect residential sorting and discriminatory practices that operated broadly across U.S. cities, rather than an additional siting effect uniquely induced by the HOLC maps, which we do not detect.