How Cities are Fighting Back Against the 'Heat Island Effect'
As temperatures rise, researchers are rethinking how cities measure and respond to urban heat. But experts say successful solutions require finding solutions tailored to local conditions rather than relying on one-size-fits-all fixes.
A woman lies on a sun lounger at Coney Island, New York. Worldwide, cities are searching for cooling solutions as extreme heat becomes a threat to public health. But experts say some solutions can fall flat depending on where they’re implemented.
Andy Buchanan / Alamy
Record-breaking heat and humidity are already upon us at the start of what is predicted to be a scorcher of a summer.
Our cities, with their dark, asphalt surfaces, exhaust-emitting vehicles, and heat-trapping buildings, feel these temperatures the most. Many residents experience at least 8 degrees of additional heat just because of their neighborhood layout, according to Climate Central, which assessed heat patterns in 65 metropolitan areas.
These high temperatures radiate starkly in contrast to surrounding suburbs on a thermal satellite map, earning the phenomenon its name: the Heat Island Effect. It’s been a guiding metric in heat mitigation since the field became widely studied over a decade ago.
The Heat Island Effect can be a helpful—if at times overly simplistic—reference point, scientists say. It raises awareness about the severity of urban heat but experts say the phenomenon can put too much emphasis on the temperature of the ground, rather than the ways those temperatures affect people. High temperatures have been linked to cardiovascular deaths, chronic kidney disease mortality and respiratory failure.
Scientists and architects have begun to search for protections from these extreme urban heat waves. What’s emerged in some places is a patchwork of green spaces, architectural innovations, and technological advancement, that might help cities find relief from searing temperatures.
These efforts require surgical precision or they can backfire. No two cities are the same, and their reasons for absorbing heat are also not the same, says Mat Santamouris, a distinguished professor of high-performance architecture at the University of New South Wales. Heat poses different problems for different cities: In some it’s a chronic condition, while in others it’s a rare but severe disaster that requires emergency preparedness. Adopting the wrong strategies can be wasteful and even detrimental.
“Every mitigation project in a city should be designed by experts and tested,” says Santamouris. “Or we risk having very poor results, spending a tremendous budget, and increasing temperature in the cities.”
Planting the right trees in the right places
One way to cool down a city? Introduce plants.
Medellin, Colombia, invested millions of dollars in “green corridors,” lush, connected thoroughfares across the city aimed at providing cool spaces and shade for pedestrians.
Santiago, Chile, pledged to plant 30,000 new trees in its metro area to provide shade and cooling for approximately a third of the country’s population.
Tree planting pledges have long been touted as ambitious fixes to environmental strife. But applied irresponsibly, they can do more harm than good, says Santamouris. “Humidity, increases in temperature.” In rare cases tree canopies can trap heat instead of shielding from it.
Considering the species of tree before planting is vital, testing if it can withstand the climate it is meant to protect from, how much water it needs, and where its shade would be most effective. For example, a tree planted in a parking lot is much less valuable to a community than one planted in a playground, says Ladd Keith, director of the Heat Resilience Initiative at the University of Arizona.
But be it greenery, architecture or reflective surfaces, these changes come at a cost, one many of the world's most heat-exposed countries simply can't afford, says Santamouris.