From cooling cities to reducing stress, the benefits of green spaces are countless: a simple stroll in nature could even boost your powers of concentration, for example.

But not all green spaces are equal when it comes to assessing cooling capabilities, according to recent research by the Global Centre for Clean Air Research, based at the University of Surrey, England.

For the study authors, their starting point was the observation that “despite many reviews, the evidence based on quantified green-blue-grey infrastructure cooling benefits remains partial, and the practical recommendations for implementation are unclear”.

To investigate the issue, the experts carried out an extensive meta-analysis, sifting through 202 papers on the subject. They compared several types of green space – such as parks, wetlands, botanical gardens, urban farms, and playgrounds – and waterways around the world, to gauge their effectiveness in mitigating air pollution and heat in the streets during droughts or heatwaves.

The study concludes that botanical gardens are the most effective type of green space for cooling city air, reducing atmospheric temperatures by an average of 5°C.

Wetlands, rain gardens (landscaping designed to collect rainwater) and green walls are also effective in reducing heat: their average cooling effect is estimated at between -4.7°C and -4.1°C.

Logically, the study shows that the larger the natural space, the greater the cooling effect. The authors also recommend that municipalities link green spaces together to form “green corridors”, and undertake greening projects that reduce carbon emissions and help prevent flooding.

“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,” study co-author Prashant Kumar noted.

Co-author Maria de Fatima Andrade, professor in the Atmospheric Sciences Department at the University of Sao Paulo, Brazil, added: “While our paper confirms just how many ways there are to keep cool, 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.”