• Cities are Surface Urban Heat Islands (SUHI), so store more heat than nature-rich areas.
  • People of colour were exposed to higher heat stress levels than white residents in all but 6 of 175 major US urban areas, according to a new study.
  • The roots of racial heat stress discrepancies could date to early city segregation practices, like redlining.

On average, people of colour live in the hottest part of town in most US cities, according to a new study. Exposure to heat stress can lead to heat-related health issues like strokes, dehydration or even premature death.

Concrete buildings, roads and infrastructure in cities hold more heat than nature-rich areas – a phenomenon known as Surface Urban Heat Islands (SUHI). But heat stress levels can also differ from one neighbourhood to the next, depending on the abundance of trees and greenery.


The study, published in Nature Communications, used satellite temperature data and US Census information, to assess the impact of SUHI levels on different neighbourhoods within 175 of the largest urban areas in the continental United States.

The results showed that in all but six urban areas, people of colour (defined in the study as including all hispanic and all who do not identify as white alone) lived in areas with fewer trees and were exposed to higher average heat stress levels than their white counterparts.

People of colour experienced average SUHI exposure levels of 3.12°C, higher than the 2.70°C average recorded in hispanic communities and more than twice the levels (1.47°C) found in non-hispanic white areas.

a chart showing the relationship of surface heat and race in US cities
Surface Urban Heat Islands adversely impact people of colour in US cities.
Image: Nature

The above chart shows racial differences across the 175 cities studied. People of colour (shown in red) are exposed to SUHI temperature increases in excess of 5.5°C, while non-hispanic white communities (shown in blue) levels rarely exceed 2°C.

Race, income and redlines

The study points to historical racial segregation practices like redlining as a potential root cause of this discrepancy.

Redlining refers to the practice of denying home loans or insurance based on an area’s racial composition, which was common in the 1930s and influenced where in a city different ethnic groups could settle.

Although the US Fair Housing Act banned the practice in 1968, its impact is still felt in many US cities. However, it’s important to note that demographic changes and urban growth in the intervening years make it difficult to accurately assess the true impact of redlining on cities today.

a chart showing the relationship between income and heat stress in baltimore
In Baltimore, the poorest neighbourhoods are also the most heat stressed.
Image: Nature

As figure (a) and (b) of the above chart show, in Greenville, South Carolina, where redlining was practiced, the population of people of colour is concentrated in areas of higher heat stress (shown as dark orange and red), while poorer neighbourhoods are located in cooler areas away from the city center.

However, in other cities like Baltimore, where the non-white population is dispersed more evenly throughout the city, figures (c) and (d) show the poorest neighbourhoods are also the most heat stressed.

What's the World Economic Forum doing about the future of cities?

Cities represent humanity's greatest achievements - and greatest challenges. From inequality to air pollution, poorly designed cities are feeling the strain as 68% of humanity is predicted to live in urban areas by 2050.

The World Economic Forum supports a number of projects designed to make cities cleaner, greener and more inclusive.

These include hosting the Global Future Council on Cities and Urbanization, which gathers bright ideas from around the world to inspire city leaders, and running the Future of Urban Development and Services initiative. The latter focuses on how themes such as the circular economy and the Fourth Industrial Revolution can be harnessed to create better cities. To shed light on the housing crisis, the Forum has produced the report Making Affordable Housing a Reality in Cities.


Tackling climate injustice

As climate change increases global temperatures, without urgent action the hottest parts of cities will inevitably get warmer, disproportionately exposing city dwellers of colour in the US to greater heat stress.

While there is no one-size-fits-all solution to resolving heat-stress inequalities, as city and neighbourhood disparities have unique characteristics from city to city, several solutions have been put forward.

In Phoenix, Nature’s Cooling Systems Project aims to implement green designs to bring about nature-based, cooler and healthier neighbourhoods to combat Arizona’s desert heat.

The initiative turns urban planning on its head, by encouraging people living in heat-stressed neighbourhoods to get involved in finding ways to cool things down, rather than relying on town planners with little experience or knowledge of local life.

Suggestions include constructing neighbourhood shade coverings, or a return to the traditional adobe buildings designed to cope with extreme heat, reports Scientific American. Alternatively, natural solutions like planting more trees and vegetation could help reduce the intensity of heat-affected areas.

Understanding which communities are at greatest risk will help policymakers and city planners find ways to eliminate racial and income disparities.