Policy Update

First in Science: City Trees Can Reduce Urban Heat Island Effect

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Clara Summers
Climate and Energy Manager

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Canopy Tree Cover Can Drastically Reduce Heat Island Effect
New research shows that 40% canopy cover is an important threshold

The urban heat island effect is well documented and increasing green spaces and tree cover can help to mitigate those impacts. Now a new study has determined the amount of tree canopy needed to significantly reduce temperatures.

The Study: Researchers took live temperature readings every five meters throughout Madison, Wisconsin. The temperatures were compared with the amount of tree canopy and the amount of pavement and building structures in that area.

Results: Researchers found an urban tree canopy of at least 40% results in the most cooling – as much as four to five degrees Celsius (seven to nine degrees Fahrenheit). Anything less than 40% canopy cover results in very small amounts of cooling.

Since this threshold was previously unknown, researchers hope this will guide strategies for increasing tree cover. Trees are often planted in wealthier neighborhoods. Therefore, distributing planting to be more equitable can help to not only lower temperatures but also bring mental and physical health benefits to the community.

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