Botanical gardens can cool the city air by around 5 degrees Celsius during heatwaves, with parks and wetlands also significantly reducing air temperatures, according to the most comprehensive review of its kind. 

Green spaces and water can reduce temperatures in cities by shading, and because water vapour given off by plants or from water bodies cools the air by evaporation. 

For their study, an international research team, including the UK Centre for Ecology & Hydrology (UKCEH), reviewed evidence of the cooling effect of natural features in more than 100 cities and towns worldwide.  

The average temperature reductions were:

 Botanical gardens  -5°C
 Wetlands  -4.7°C
 Rain garden   -4.5°C
 Green walls  -4.1°C
 Street trees  -3.8°C  
 City farms  -3.5°C 
 Parks  -3.2°C 
 Reservoirs  -2.9°C
 Playgrounds  -2.9°C 

While there was variation depending on local factors, there were some general patterns and, by and large, the larger the area of green space or waterway, the greater the cooling effect. 

The study was led by the University of Surrey and involved around 30 scientists from five countries, including Dr David Fletcher and Professor Laurence Jones of UKCEH.

Professor Jones explains: “Our study provides comprehensive evidence of the extent of the cooling effect of green spaces and waterways, and identifies features where we need more information on their cooling potential. 

“In addition to reducing temperatures in urban areas, green and blue infrastructure projects can also store carbon, improve air quality and reduce flooding.

“Our research will therefore help town planners make cities more resilient to the effects of climate change, as well as improving the health and wellbeing of their residents.” 

The study, carried out as a part of the UKRI-funded RECLAIM Network Plus, is published in the journal The Innovation.

Paper information

Kumar et al. 2024. Urban heat mitigation by green and blue infrastructure: drivers, effectiveness, and future needs, The Innovation. DOI: 10.1016/j.xinn.2024.100588. Open access.