Which cities are the world's coolest

Green wall in Taipei, Taiwan - green walls can deliver a 4.1°C cooling effect. Image: Nadine Marfurt on Unsplash

If you want to know which of the world's cities are coolest, maybe check out their wetlands, parks and even botanical gardens.

Researchers at the University of Surrey in the UK say these features are among the best ways to cool cities down during heatwaves. Botanical gardens are not just beautiful, they say, but can cool air by 5°C during heatwaves. Parks (3.2°C) and wetlands (4.7°C) have a similar effect.

"By implementing just some of the measures we describe, cities can become more resilient, and their citizens can be healthier and happier too."

Professor Prashant Kumar, University of Surrey

The researchers say this is the most comprehensive review of its kind, and analysed how green spaces and waterways cool down cities and towns.

Professor Prashant Kumar, director of the University's Global Centre for Clean Air Research, said: "We have known for some time that green spaces and water can cool cities down. However, this study provides us the most comprehensive picture yet.

"What's more, we can explain why. From trees providing shade, to evaporating water cooling the air."

The team found that while success depends heavily on local factors – there were some general patterns. Among the green spaces and natural features considered were botanical gardens, wetlands, raingardens, green walls, street trees, city farms, parks, reservoirs and children's playgrounds.

Boston Public Garden, US. Image: Josephine Baran on Upsplash

Generally speaking the bigger the park – the bigger the cooling effect, but cities can unlock greater benefits by connecting green spaces into green corridors. Greening projects can also remove carbon emissions and even help prevent flooding.

Professor Kumar said: "This will help town planners around the world confront the challenges of global heating. By implementing just some of the measures we describe, cities can become more resilient, and their citizens can be healthier and happier too."

However – the team also found areas of the globe which were vulnerable to heat – but had not researched the best way to use green spaces to cool down.

Professor Maria de Fatima Andrade from the atmospheric sciences department at the University of Sao Paulo, Brazil, said, “Our paper confirms just how many ways there are to keep cool, but it also reveals how much work is left to do. Institutions around the world need to invest in the right research – because what’s very clear from our study is that there is no one-size-fits-all solution. It depends on what works for your community.”

The study is published in the journal, The Innovation.