Significant thermal disparities exist among predominantly white, Black, Hispanic and Asian communities in America’s 200 most populous cities, according to new research from IUPUI’s Daniel Johnson.
In the study, published in the International Journal of Environmental Research and Public Health, Johnson examined surface urban heat islands, areas within a city that experience much warmer temperatures than their surrounding landscapes. The research will expand understanding of the dynamic nature of inequitable urban heat exposure and provide new insight into actions cities can take to improve the lives of residents.
“Previous research has really shown just a snapshot in time of the disparities that exist between communities of color and predominantly white populations, but I wanted to analyze the differences over time,” said Johnson, an associate professor of geography at the IU School of Liberal Arts at IUPUI. “This study showed that we are seeing an increase in this geographic disparity of temperature. This is likely due to continuing environmental degradation in warmer areas of the city as a result of poverty and increased temperatures creating a positive feedback loop.”
Johnson examined 44,476 predominantly white, Black, Hispanic and Asian census tracts – a method used by the U.S. Census Bureau to analyze populations – and surface heat island intensity – a measure of the disparity between the temperatures of surface urban heat islands relative to the surrounding areas – during the summer months in 2003 to 2018.
The study found it would take until 2363 for predominantly white communities in U.S. cities to reach the same temperature as Black prevalent ones, white communities will reach thermal parity with Asian communities in 2152, and they will never catch up to Hispanic communities since they are warming at the same rate.
“These results demonstrate the degree of difference in the current temperature regimes for each demographic group,” Johnson said. “The simple fact that it will take over 300 years for white prevalent urban census tracts to reach thermal parity with Black prevalent urban tracts is an alarming observation and one that should heighten awareness of this issue. Hopefully, policymakers can use such findings to illicit change and work toward creating better environmental conditions for those most affected.”
He also ranked the top 25 American cities by the highest levels of surface urban heat island intensity during the 16-year period.
New Orleans, Louisiana, had the highest surface urban heat island intensity for both Black prevalent communities (nearly 6 degrees Celsius higher than the average temperature for the city) and predominantly white communities (around 5.5 degrees Celsius higher). San Jose, California, was the highest for both Hispanic (around 7 degrees Celsius) and Asian prevalent communities (around 7 degrees Celsius).
In Indiana, Indianapolis was the 14th warmest city in the country for predominantly Asian communities (around 3 degrees Celsius warmer). Gary, part of the Chicago region, was the 16th warmest for predominantly Black ones (over 3.5 degrees Celsius warmer), 18th for white prevalent communities (around 2 degrees Celsius warmer) and 20th for Hispanic prevalent communities (over 4 degrees Celsius warmer). South Bend was 22nd amongst predominantly white prevalent communities (over 2 degrees Celsius warmer).
Johnson also found that segregated cities tend to be warmer than non-segregated cities, ones with a good integration of the census tracts examined. The level of residential segregation is a factor in the observed thermal disparities between cities. When measures of segregation are high, temperature differences between groups appear most pronounced.
According to Johnson, one of the major reasons for the disparities experienced in urban temperatures is due to the “redlining” practice that occurred in the 1930s, where government-sponsored organizations outlined predominantly Black neighborhoods in red on maps, signifying them as being “hazardous.”
“The grading of neighborhoods that took place in the 1930s has continued to marginalize these urban areas and reinforce some of the structural racism that we’re experiencing now,” Johnson said. “Remnants of this practice are still persisting, but I hope this research can help lead to more awareness of this and ultimately stimulate ways to disrupt or improve the conditions of these highly vulnerable locations.”
As global temperatures continue to rise, Johnson said some of the communities he examined may become unlivable in the summer months due to the scorching temperatures and the associated health effects. He hopes the research can help guide policymakers and local organizations in protecting our most vulnerable communities.
“This is a very complex problem, and there will not be one solution to it,” Johnson said. “Urban planning can play a big role, but it will take more than that, because this issue will not be solved overnight. It is going to take an inter-generational effort to break this down and have the greatest impacts on making these communities safer for their residents.”