More trees don’t always mean cooler cities

The urban heat island effect combined with climate change is making cities around the world hotter. One response has been to plant more trees, but a new report in The Conversation looks at research from Melbourne, Munich and Hong Kong that suggests a ‘one size fits all’ approach doesn’t work.

The research took place over summer in the three cities. Open streets with no vegetation were compared with streets containing only trees, and streets with trees, shrubs, and ground cover. Researchers found that while trees bring shade, depending on the climate of the city, sometimes shrubs and ground cover either added a cooling effect, or trapped humidity and restricted air flow. 

In temperate Melbourne, adding trees reduced radiant heat by as much as 18°C. In cooler Munich, layered planting lowered afternoon heat by up to 8°C. In subtropical Hong Kong, however, dense vegetation sometimes increased humidity, reducing the overall cooling effect. Dense planting can also slow the dispersal of exhaust pollution in narrow streets, potentially affecting pedestrian comfort. These findings highlight the importance of considering street width, climate and airflow when introducing trees and greenery into urban environments.

Rather than taking a generic approach, climate smart planting is the best way to create cooler, more comfortable cities around the world. 

Read the full article here.