Will more trees cool the streets that need it most?

During a heatwave, you can feel the city change from street to street. One road shimmers with heat coming off the asphalt. Five minutes away, a leafy street feels almost liveable. For most of us, a heatwave is a hard week that passes. For millions of others, this heat is the everyday climate, with no escape. So it matters whether planting more trees cools the streets that need it most, or mostly benefits neighbourhoods that already experience lower temperatures.

It is tempting to treat trees as a thermostat. More green, less heat. The reality is messier, and that is what makes it interesting. Heat in a city is not evenly distributed, and neither is the greenery that mitigates it. To see where planting works and where it barely helps, you need to map a whole city at once.

Reading cities from above

That is what Monika Kuffer does. She is a professor and expert in remote sensing. She reads cities from above using satellite data. She measures the temperature of the city’s surfaces, its roofs, roads, and patches of green, and links it to the shape of the neighbourhood underneath.

The pattern is not random. Working across a string of European cities, a study supervised by Monika has shown that the form of a street shapes how hot its surfaces get. How tightly the buildings pack together, how much of the ground is dark and paved, how much green breaks it up: these decide how much heat a place holds. And the hottest, most paved, least green streets are rarely where the wealthy live.

This is why the leafy street wins. Trees do not just look cooler. They shade the paved surfaces that would otherwise soak up the sun, and they release moisture that pulls heat out of the air. Where a street has neither shade nor greenery, the asphalt and brick bank the day’s heat and hand it back long after sunset. Into the rooms where people are trying to sleep.

Read the full article on UT Stories: the online platform that covers the latest research by pioneering scientists and student life at the University of Twente.