Mapping Urban Heat Risk Inequality in Los Angeles

Click on the photo below to explore the interactive app:

Mapping Heat Risk Inequality, an R Shiny App developed by myself and Natalie Smith

Background

What is Redlining?

The Home Owners’ Loan Corporation (HOLC), established during the New Deal to stabilize the housing market amidst the Great Depression, aimed to assist struggling homeowners. However, HOLC’s operations also perpetuated racial discrimination in mortgage lending, reflecting prevailing attitudes of the time.

Between 1935 and 1940, HOLC created area descriptions and color-coded maps to evaluate neighborhoods’ mortgage security. HOLC’s criteria included housing quality, property values, and residents’ racial and ethnic backgrounds. These maps categorized areas into four types:

• ‘Type A’ neighborhoods outlined in green were considered the most desirable for lending, typically affluent suburbs;

• ‘Type B’ neighborhoods outlined in blue were still desirable;

• ‘Type C’ neighborhoods outlined in yellow were declining;

• ‘Type D’ neighborhoods outlined in red were the riskiest for mortgage support, often older districts in city centers and predominantly Black and People of Color.

These grades were used for redlining, restricting mortgage financing and homeownership opportunities, particularly in communities of color. These discriminatory practices continue to shape urban inequality today.

HOLC map of Los Angeles County, 1939. Image from Mapping Inequality, University of Richmond’s Digital Scholarship Lab.

Environmental Implications

Environmental disparities in American cities reflect historic redlining policies that favored wealthy, predominantly white neighborhoods over poorer, often minority communities. Wealthier urban areas tend to have more parks and trees, which combat the urban heat island effect by providing shade and cooling the air temperature. A study led by scientists in 2017-2018 used HOLC redlining maps to investigate the link between discriminatory housing practices and contemporary environmental stressors, particularly heat islands. They found that areas previously redlined by HOLC were significantly hotter than greenlined neighborhoods during summer months, mainly due to differences in surface materials and tree canopy coverage. Subsequent research has confirmed these findings, highlighting the enduring impact of past discriminatory policies on present-day environmental inequalities and public health outcomes.

Health Implications

The mechanisms through which historic redlining influences present-day public health are an ongoing topic of study. Potential contributing factors include economic isolation, disparate property valuation, and environmental exposures.

Research on redlining and health has intensified since the digitization of HOLC maps, revealing associations between redlined areas and various health indicators such as mortality, pre-term birth, cardiovascular disease, and COVID-19 infection burden. Redlining has also been linked to environmental determinants of health, such as air pollution and access to healthcare services.