Trees Halve Heat Retention in Cities

Researchers from Western Sydney University, the University of New York, and the Pacific Northwest National Laboratory analyzed data from nearly nine thousand cities worldwide, home to roughly 3.6 billion people. Their work shows trees reduce heat retention from the urban heat island effect by almost 50 percent. Cities typically run 1 to 3 degrees Celsius warmer than surrounding rural areas due to heat absorption from asphalt and concrete.

The study modeled a scenario removing all tree cover to accurately measure cooling effects, unlike previous studies using surface temperatures. Results indicate trees lower local air temperatures by at least half a degree Celsius for over two hundred million people. However, the cooling effect varies; cities like Phoenix, USA, see more pronounced temperature differences with increased tree cover.

The researchers note that wealthier, suburban, and more humid cities tend to have more trees, creating an inequality in access to natural cooling. While planting trees helps, it will only offset roughly 10 to 20 percent of expected heat increases by mid-century, requiring broader strategies like reflective materials and green spaces. The work continues to refine urban heat mitigation strategies.