In Boston, a city that has seen record-breaking heat and overwhelming rainfall totals over the past two summers, where you live can determine how extreme that weather can feel.

Take, for example, Jamaica Plain where recorded temperatures are cooler than in neighborhoods such as Roxbury and Dorchester.

The stark contrasts are partly the result of two overlapping issues: Boston being an urban heat island, and the city’s history of redlining. Several studies on climate and heat in the city, including the city’s own 2022 heat resilience report, show Boston is generally warmer and more susceptible to extreme heat than surrounding cities and suburbs. But within the heat island are even warmer hot spots, including neighborhoods that were once targeted by racist lending practices and are filled with mostly Black, Latino, and Asian residents today.

“If you overlay Boston’s heat maps with maps of formerly redlined neighborhoods, it’s pretty striking, the overlap that’s there and the correlation that’s there,” said Isabella Gambill, the assistant director of climate, energy, and resilience at A Better City, an environment and infrastructure-focused nonprofit in Boston.

Inspired by Boston’s heat resilience research, Gambill’s nonprofit is currently working in partnership with the City of Boston, The Boston Foundation, and the Boston University School of Public Health to collect real time temperature data from Boston’s hottest neighborhoods. As part of the study, A Better City is placing temperature reading sensors in seven communities: Roxbury, Dorchester, Chinatown, Mattapan, East Boston, Allston-Brighton, and Jamaica Plain. The aim is to collect data that could lead to a permanent network of real time data-collecting sensors that reveal how much hotter these areas are compared to surrounding ones.

In the fall, the researchers will analyze the reports and compare them to readings from Logan Airport, where the city gets its official temperature readings.

The project will be one of the most up-to-date studies on heat disparity in Boston. It adds to several other studies that document temperature differences across the city or try to quantify communities’ vulnerability to extreme heat.

Many of those reports are a few years old, and the data in them are often either recorded at one point in time or based on temperature models instead of real-time sensor data like A Better City’s project. Still, their results are striking and point to the same conclusion: that structural racism of the past continues to affect how Boston residents experience heat today. Here is some of what those studies found:

Redlined areas are hotter

Throughout the mid-20th century, housing officials across the country discriminated against Black and Hispanic home buyers. Policies shut them out of nicer neighborhoods and confined them to districts that the Home Owners Loan Corporation, or HOLC, outlined on housing maps in red ink so that real estate professionals could deny loans in those areas and steer middle- to upper-class white people away from them. Over time these areas became less developed and more vulnerable to a host of social, financial, health, and environmental issues.

As a result, people living in those same neighborhoods suffer today from more extreme heat.

“Understanding and acknowledging the historical context of disinvestment and subsequent effects on the built environment in Boston is critical to planning for heat vulnerability and resilience,” wrote the authors of the city’s 2022 heat resilience report.

The report measured air temperature models to estimate differences across the city at 3 p.m. on one day in July 2019. It revealed that formerly redlined areas on average are about 3 degrees hotter than the citywide average and up to nearly 8 degrees hotter during the day compared to areas that weren’t redlined.

In a separate report that same year, the Museum of Science collected temperature data throughout Boston over a two-week period in July. The results showed that certain areas were disproportionately hotter during the day and night. When compared to HOLC redlining maps from 1938, the research showed clearly that many of the hotter areas were also neighborhoods that were redlined, such as Chinatown and parts of Dorchester.

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Redlined areas have fewer resources to cool down

As a result of redlining, Gambill said, certain neighborhoods attracted more industrial investment than residential and green space projects.

Those neighborhoods now have less tree coverage than other areas, more pavement, and fewer resources for relief. Residents in these areas also have lower income than other areas. All these factors contribute to “heat vulnerability,” a measure of how sensitive a population is to heat-related issues, including heat stroke and heat exhaustion.

According to the city’s heat plan, areas in Boston that were redlined have about 40 percent less tree coverage than non-redlined areas. Data from a separate study from Boston Parks and Recreation show what this disparity looks like on a map.

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Redlined areas are more vulnerable to heat-related issues

Redlining didn’t just make communities hotter, it made them less wealthy and more prone to medical issues. Researchers use all of these indicators to calculate heat vulnerability. The US Census, for instance, used American Community Survey data such as income, employment, language barriers, health insurance coverage to determine “community resilience” to heat.

The results show that census tracts in Roxbury, Dorchester, and East Boston — neighborhoods that are largely Black and Latino — are more vulnerable to heat.

Another map by researchers at Yale University looked at additional factors such as land cover, average temperatures, and the prevalence of diabetes to create a heat vulnerability index. The results were similar to the census’ index, showing Roxbury and Dorchester as disproportionately vulnerable to heat.

The heat disparities in Greater Boston have also reached national conversations related to the ongoing climate crisis. Representative Ayanna Pressley of Boston brought the local issue to Environmental Protection Agency leaders during a July House Committee on Oversight and Accountability.

“When my colleagues across the aisle use platforms like this hearing to pretend that climate change is some hoax, I can’t help but think about the stories I hear from our youth when I’m back home,” Pressley said during the hearing. “The City of Chelsea, a predominantly Hispanic community in my district, can be 10 to 15 degrees hotter than neighboring communities in the Boston area on a given day.”