The Blue Gap: Redlining, Historic Wetland Decline, and Flood Risk in the United States

Abstract

Wetlands have recently been recognized for the extensive ecosystem services they provide by absorbing carbon, regulating biodiversity, filtering water, and reducing flooding intensity, despite their historic devaluation and destruction. The natural buffer wetlands provide to the impacts of sea level rise and storm surge is increasingly valuable for low-lying and often low-income minority communities in the face of climate change. But a study of wetlands through an environmental justice framework, in terms of the relationship between redlining and wetland decline, has not yet been conducted on a national scale in the U.S. This thesis thus addresses gaps in the literature, one on the relationship between redlining and historical wetland loss at a multi-city national scale, and one on the relationship between redlining, wetland loss, and flood risk. Through a sequential mixed-methods design involving the digitization of 112 historic wetland maps, GIS spatial analysis, spatial regression, and then qualitative case studies, I investigate these dynamics across ten U.S. cities from around 1900 to 1940, 1940 to 2025, and 1900 to 2025, thus observing rates of decline before and after redlining. I find that there is a statistically significant relationship between redlining and wetland loss from 1900 to 2025 in my most robust city-pooled sample model, where a one-step decrease in HOLC grade is associated with a 3.176 increase in percentage points of wetland loss. However, I determine through observing city-level heterogeneity in this relationship that it is geographically and contextually contingent. Similarly, I find that these dynamics shape climate exposures differently across demographic groups. Some cities, like New York City, evidence a strong, significant trend in wetland loss by redlining grade, correlating with higher flood risk for minority communities, where wetlands were in low-lying and industrially undesirable areas. Other cities, like Minneapolis, invert this trend, where wetlands were destroyed along idealized waterfront areas with higher-income, majority-white populations. Overall, this thesis finds that the destruction of wetlands has been socially produced through targeted policies in the mid-century, but to different effects across cities. Targeted policy interventions, taking into account typologies of systematic wetland destruction, can address this to achieve more just conservation, restoration, and community resilience to flooding and storm surge.