Tree cover and street temperature

A research team investigating summer heat compared two neighboring streets. One had mature trees; the other had young trees with small crowns. At midday, pavement beneath the mature trees was considerably cooler. The team initially expected the cooler street also to have cooler air throughout the day. However, air sensors showed only a modest difference, and that difference almost disappeared after sunset.

The researchers explained that shading primarily changes how much sunlight reaches a surface. Air moves between shaded and unshaded areas, reducing local differences in air temperature. Consequently, a photograph showing a very cool patch of pavement cannot by itself establish that the surrounding neighborhood has become equally cool.

The study still found a practical benefit. Pedestrians waiting beneath mature trees reported greater comfort because less heat reached them from the sun and nearby surfaces. The researchers therefore recommended tree cover near places where people wait, rather than treating pavement temperature as a complete measure of neighborhood cooling. They also cautioned that their comparison involved only two streets, whose buildings differed slightly in height.