Taking "Urban Heat Islands" Seriously

If you’re low-income and Black urban settings like Philadelphia, it’s pretty likely you've been redlined - against your will - into a space where the temperature is hotter than most

an ecoWURD feature

As temperatures continue soaring, now beyond record-breaking territory, populations, their governments and media are now found paying much closer attention to the devastating impacts of heat. No longer is this an isolated incident or a random wildfire or two. The outbreaks of near napalm-feeling heat are fairly worldwide, with thousands suffering under domes of carbon-instigating hotness. The scale of that suffering is nowhere more known than in cities. Or, more specifically, the most struggling parts of the cities.

There is now a lot of discussion about urban heat islands. We’re glad many finally noticed … after, of course, running out of cool or untouched spaces to escape to. If only, however, for a few moments, corporate media outlets can quit their silly camera takes of kids running through downtown water fountains and the crowds of people at beaches and pools - as if the apocalyptic heat is fun when, obviously, it’s not - we could get somewhere with telegraphing the urgency to the general public. Urban heat islands are deadly. And they hit already hard-hit populations hardest: those are the ones that are mostly Black and some Brown and mostly low income. Many have little means for cooling other than a fan that blows more hot air or a window air conditioning unit or two that will only blanket partial space. So if you live in an urban heat island - it’s safe to assume you already know you do, you just don’t know what to call it - and you’re low-income and Black in Philadelphia, it’s pretty likely that you have been redlined into that urban heat island (otherwise acronymed as “UHI”).  As researchers concluded in a 2021 issue of Nature Communications …

We find that the average person of color lives in a census tract with higher SUHI intensity than non-Hispanic whites in all but 6 of the 175 largest urbanized areas in the continental United States. A similar pattern emerges for people living in households below the poverty line relative to those at more than two times the poverty line.

Let’s talk about UHIs. They occur when cities become hotter than their surrounding areas. Neighborhoods within cities also can become urban heat islands when their temperatures rise. Still, how do you know if you live in one? 

The Heat Comes Out at Night

When it’s hot, does it feel like your neighborhood is even hotter compared to another neighborhood you happened to go to, shop in or catch a mass transit bus through? Also, is your neighborhood experiencing high rates of violent crime? If you’re nodding you’re head “yes,” you’re probably living in an urban heat island. UHIs are typically two to seven degrees hotter than the surrounding areas -- and sometimes even hotter than that. We see numerous examples of watching a dashboard thermometer rise anywhere from 10-20 degrees when driving from one very cool and greened spot of a city into a part that has very few trees. These places also don’t cool down at night.   

The reason UHIs don’t cool down at night is because they predominantly occur in areas where cement and asphalt dominate the landscape. These materials absorb the heat and hold on to it, so while other neighborhoods cool down in the evening, UHIs don’t. Look around your block. What are the buildings and grounds made of? If all you see is cement, brick and asphalt, you probably live in an urban heat island. That’s also creating increased rates of violence, as researchers in The Conversation noted …

Between 1996 and 2013 in Finland, every 1°C increase in temperature accounted for a 1.7% increase in violent crime across the country. It has even been estimated that 1.2 million more assaults might occur in the United States between 2010 to 2099 than would without climate change.

Keep looking around. Do you see any trees? Gardens? Water features? If you don’t, you’re probably living in a UHI. Trees provide shade to people, as well as shade for pavement and buildings. They also remove heat from the air. By planting trees, the temperatures of people and infrastructure can be brought down, reducing the threat of an urban heat island.  They figured this out in Medellin, for example, Columbia’s second largest city of over 4 million people. There they built a network of 30 interconnected green corridors that helped drop temperatures citywide by 4 degrees.

Gardens also can provide open spaces where air can flow while absorbing heat from the atmosphere. If your building has a black tar roof, it is going to absorb the heat and increase the temperature of the entire building. If, instead, you had a garden or a full set of shrubs planted on a rooftop, they could help cool the entire building. If your building has a black tar roof, you’re probably paying a higher electricity bill trying to cool your place, too … and that’s if you have air conditioning.   

People that live in urban heat islands are usually forced to pay for cooling themselves, but there’s a lot that the city of Philadelphia can do to reverse the causes of urban heat islands, cool communities, reduce the cost burden to residents -- and reduce violent crime, too.   

Cool Cement

In addition to planting trees and gardens and installing cooling infrastructure like water features, cities can use lighter color cement when paving and repaving roads. Using lighter colors will prevent roads from absorbing as much heat. With less heat absorbed, the temperatures can go down. The city also can spray streets with water on hot days. This is a technique used in Japan. Another technique that can be used to cool UHIs is to paint buildings with reflective paint that can prevent heat absorption and keep temperatures down.  

Cities like Philadelphia and elsewhere could also pass legislation that requires landlords to ensure apartments maintain livable temperatures. There is a policy that requires landlords to keep their units above 68 degrees in colder months. There is no policy requiring them to keep their units cool, though. These efforts can be coupled with programs that help landlords install solar air conditioning units so tenants can keep cool without adding to the larger climate crisis. Solar panels can also be used to keep schools cool and supplied with clean energy. At a time when schools in Philadelphia are closing because they can’t keep students cool, these solutions also can be effective in helping to keep the education system functioning.   

Imagine a hot summer day in your neighborhood. Now re-imagine that same day if your home had functioning AC. Imagine if there was a garden on top of your roof and trees planted outside. Imagine a cool breeze flowing down your block. Imagine lower electricity bills, less violence and a higher quality of life. We can eliminate urban heat islands and live more comfortably by making these very simple investments in our neighborhoods now.