By James Parker, Catherine E. Scott, James B. McQuaid, and Thomas J. Sloan

This Plain Language Summary is published in advance of the paper discussed. Please check back soon for a link to the full paper.

The aim of our research was to understand how trees in cities can keep people cooler during hot weather. Cities heat up more than the countryside because our buildings reflect less of the sun’s energy and store heat for longer. This makes people more uncomfortable and is particularly a risk for people with certain health conditions. We wanted to measure real differences in temperature within the city’s greenspaces and woodlands and find out which have the greatest cooling effect.

To measure differences, we installed a network of sensors across Leeds, England, measuring air temperature and humidity every 15 minutes through the summers of 2023 and 2024. The sensors were on busy streets, small city‑centre parks, larger suburban parks and different types of treescapes such as larger woodlands or small groups of trees. By comparing conditions in these locations, we were able to understand how they behaved during warm summer periods.

Our results found that treescapes were the coolest places in the city. They were, on average, around 1.4°C cooler than nearby built‑up streets, and during the hottest summer periods were up to 5°C cooler in the middle of the day. Larger parks and smaller city-centre parks provided some cooling effect, but this was less effective than in the woodland areas of the city. We used a human thermal comfort index to demonstrate that treescapes significantly reduced the number of hours under high levels of heat stress when compared to the built environment that surrounds them.

The results we’ve presented are important because they show that trees can actively protect people’s health, in addition to their other benefits. Areas with more tree canopy cover had far fewer hours that would be considered uncomfortable and that are linked with increased ill health. Our evidence shows that planting and protecting trees is a practical and effective way to make cities safer, healthier and more comfortable, especially as our climate continues to warm.

Our research shows that treescapes are one of the most effective means we have for keeping cities cool, and they should be considered as an essential part of our urban environments.