City Trees Dramatically Reduce Neighborhood Heat Islands

Densely built urban areas are considerably hotter than semi-rural and rural areas around them. A new study concludes that urban tree cover can have a dramatic impact on temperatures. According to research by Carly Ziter, extensive tree canopy cover in urban areas can dramatically reduce temperatures in their immediate environment.

In the new study, published in the journal Proceedings of the National Academy of Sciences, Ziter presents a non-linear relationship between tree cover and temperature reduction: once a certain threshold of tree cover is reached, temperatures begin to drop dramatically compared to beneath that threshold. Ziter says that tree planting would most effectively help to reduce temperatures in neighborhoods near the 40 percent tree cover threshold.

Ziter points out that areas with heavy tree cover and those that don’t have trees can be four or five degrees Celsius higher, even within just a few hundred meters.

The impact of shading trees contributes to temperature decreases during daylight hours, but it is not the only beneficial contributing factor. The water vapor given off by the trees also acts to lower temperatures. Ziter’s research shows that when the sun goes down there is a much smaller difference in temperature.

Ziter also notes that trees tend to be in wealthier areas and would like to see planting distributed more equitably. Tree planting efforts in low income areas would not only help lower the daytime temperatures, it would also contribute to the mental and physical health of people in those neighborhoods.



Photo: “She was waiting in hidden garden” by Igor Spasic is licensed under CC BY 2.0