How cities are heat-proofing for climate change

Posted: December 05, 2024

Back in 1966, folk-rock group The Lovin’ Spoonful released their only top-ten hit with ‘Summer in the City’, at least in part a lament over suffocating urban heat: 

Hot town, summer in the city
Back of my neck gettin' dirty and gritty
Been down, isn't it a pity?
Doesn't seem to be a shadow in the city
All around, people lookin' half dead
Walkin' on the sidewalk, hotter than a match head

The lyrics have only gained relevance in the decades since. This year is already on track to be the hottest on record, a trend mirrored over the past ten years. In cities, the heatwaves that have swept the globe are further exacerbated by the heat island effect: with less vegetation and water, an abundance of pavement and reflective surfaces, and all the heat produced by cars, air-conditioning and buildings in general, daytime temperatures in urban areas can be up to 7 degrees Fahrenheit (around 4 degrees Celsius) hotter than outlying regions.

More extreme heat has a real impact on human health, particularly among vulnerable populations. Heat-related deaths in the US spiked in 2021 and 2022, for example—both years that featured several notable heatwaves.^[1] In response, many cities have started innovative projects to heat-proof their infrastructure and lower risks for residents.

How cities are addressing urban heat islands

In the small Dutch city of Arnhem, city leaders started taking adaptation more seriously a few years ago, after a heatwave and an earlier flooding event put the risks in stark relief. One of the solutions they came up with: shrinking underused roads to replace them with planted areas, which both cool down the area and serve as storm drains during heavy rains. 

Medellin, Colombia, also started creating green corridors in 2016 to lower heat and improve air quality. Today, the city boasts more than 30 of these avenues linking its parks, featuring more than 800,000 new trees and millions of smaller plants. They are complemented by vertical gardens and reduce temperatures by up to 8 degrees Fahrenheit (4.5 degrees Celsius). They also offer a wealth of co-benefits, from boosting cycling to preserving biodiversity. 

Back in Arnhem, authorities have also started mapping areas that provide outsize benefits by staying undeveloped—like open, windy spaces near the river—as well as neighborhoods that face the most intense heat stress. Gathering this kind of data is crucial to guide individual infrastructure or building projects, or even inform broader planning policy that takes heat stress into account.

Other cities have adopted a similarly data-led approach. In 2021, conservation nonprofit American Forests released a Tree Equity Score that correlates urban areas’ physical characteristics—from tree canopy to surface temperature to building density—with socio-economic metrics. It found a strong correlation: white-majority neighborhoods in the U.S. enjoy 33% more tree canopy than communities of color, for example. 

The tool quickly gained traction to guide where communities should plant trees to achieve greater heat equity. Within a year, cities including Tucson and Phoenix had adopted their own tree equity goals. This year, Phoenix city council unanimously approved up to $14 million to add trees and shade over the next five years.^[2]

“We’ve seen research showing that in our corridors where we plant a lot of trees it can make as much as a ten-degree [Fahrenheit] difference in terms of summer heat temperatures,” the city’s mayor, Kate Gallego, said. 

Creative urban planning to reduce heat stress

Planting trees instead of adding more steel and concrete is perhaps the most straightforward approach to cooling urban environments. But the threat of heat stress has also bred more innovative solutions. 

In Abu Dhabi, where summertime temperatures regularly soar past 100 degrees Fahrenheit, architects have devised a new design for a pocket park featuring a canopy with movable shades, which provide protection from the sun during the day and can be opened at night to let hot air escape. Benches take advantage of shade from nearby buildings, water sprayers offer a cooling mist and strategically placed walls help to both channel a breeze and block heat from passing cars. 

The concept could provide a blueprint for drought-prone cities or those with little space for large-scale planting. Architecture firm CBT, which is behind the design, even wants to bring it to American cities, such as Boston, which could already be several degrees hotter by mid-century. 

The Middle East is “probably a decade or so ahead in thinking about sustainability, because they have to be, on issues of heat and comfort,” says Kishore Varanasi, principal and director of urban design at the firm. “They know the problem, and they’re trying to get ahead of it.” 

Looking to the past for better building design

With some of their ideas, the architects are looking to the past as well as the future: the breeze-channeling layout of the pocket park’s walls was inspired by sikkak, the narrow alleyways found in many Middle Eastern cities. Other projects have similarly drawn inspiration from ancient techniques, while looking beyond the streetscape into individual buildings. 

Elsewhere in Abu Dhabi, one skyscraper has adopted a high-tech shading system inspired by latticed screens common in ancient Islamic architecture. These mashrabiya, which keep buildings cool by diffusing sunlight, now wrap around most of the building’s sides in repeating geometric patterns, unfolding like an umbrella in response to the sun’s movement. Another tower in Qatar uses a similar concept, with butterfly-shaped aluminum elements forming an outer layer around its glass facade to offer protection from the sun. 

In China, architects are similarly drawing inspiration from skywells, narrow central courtyards that featured in homes as far back as the 14th century. The shafts create a pathway for hot air to escape, but can also create cooling airflows and provide even more relief when combined with evaporation from water features.^[3]

In the eastern Chinese city of Jinan, an 18-story office tower completed in 2022 has transplanted the concept wholesale: the architects included a modern skywell stretching from the fifth to the top floor, flanked by elevators, toilets and meeting rooms. 

Using sensors and data to map heat risk  

On the other hand, projects have also started to take advantage of everything modern technology has to offer. Perhaps the best example of high-tech climate adaptation—and sustainable building design, in general—is The Edge, an office building in Amsterdam.  

Its features include dynamic windows, automatic shades and displacement ventilation. But it also contains thousands of sensors that track people’s movements as well as light levels, humidity and temperature, in order to flexibly adjust heating, air conditioning and lighting in different areas. 

At the city level, measuring and visualizing data can be useful to get a better sense of the issue before tackling heat stress in the first place. Cities such as New York and Toronto have developed heat maps to identify hot spots and target interventions, such as planting trees, using air and surface temperature data. 

Researchers at the University of Wisconsin, for example, installed 150 temperature and relative humidity sensors on streetlight and utility poles in and around Madison, taking measurements every 15 minutes. Madrid has similarly installed a network of meteorological sensors that track temperature, humidity and other metrics across the city.

In Phoenix, Arizona State University took a more high-level approach—literally. Over a period of 14 years, they used satellite data—including NASA’s LANDSAT thermal data, which is available for cities across the globe—to examine changes in the city’s surface urban heat island in relation to changing land use cover.^[4]

Efforts like these can help inform where cities target their efforts. And with the resulting interventions, summer in the city might become just a little more bearable.

References

^{[1] https://www.epa.gov/climate-indicators/climate-change-indicators-heat-related-deaths
[2] https://www.kjzz.org/2024-02-07/content-1870630-phoenix-leaders-approve-14-million-trees-and-shade
[3] https://www.thecommons.earth/blog/cooling-architecture-exploring-skywells  
[4] https://www.epa.gov/heatislands/measuring-heat-islands#identifying}