How do trees reduce extreme heat?

Picture yourself walking outside on a sunny summer day. Where do you feel hottest, and where feels cooler? If you’re looking for shade, one of the most common places to find it is under a tree.

Now imagine that on a larger scale. A city street with concrete sidewalks, asphalt paving, and no trees, or a block with a large tree in front of each house. Trees—and, by extension, forests—have a great deal of power as buffers for extreme heat and humidity!

There are two primary ways trees help reduce extreme heat: through evapotranspiration and providing shade.

Our bodies sweat to cool us off, but in extreme heat and humidity—a 95°F air temperature with humidity approaching 100%, for example—we reach our limit for reducing heat, and sweating no longer helps.

That’s where trees come in! Water that evaporates from tree leaves into the atmosphere during photosynthesis provides a cooling effect, helping to reduce humidity to a point where our bodies can better cope.

This is especially important for remote or rural areas where people might not have access to air conditioning. Surrounding forests can reduce the temperature!

Trees also provide a more obvious form of cooling: shade! Let’s take cities as an example. In addition to there being fewer trees, there is often concrete. Concrete and other building materials reflect heat into the atmosphere, whereas trees help absorb it. As a result, the temperature in a city can be significantly higher than in the less urban areas around it. This phenomenon is called the urban heat island effect.

Many cities are working to address this by planting trees and vegetation on streets, porches, and roofs. Having trees cover over 40% of a city block provides the largest cooling effect. It can reduce temperatures up to 9°F!

Climate change is making extreme heat worse, harming the most vulnerable people, particularly folks working outside or in homes without air conditioning. In fact, the number of days where outdoor workers must endure hazardous heat conditions has quadrupled. That makes tree cover more important than ever.

Helping reduce extreme heat is just one of the many benefits of forests. They also reduce the risk posed by other extreme weather. Trees can help buffer the impact of floods, for example, by anchoring soil and preventing erosion.

The world needs more forests! This means preserving existing forests and restoring deforested land. And urban forests are just as important. You can get involved in your local community to support additional tree cover and replace concrete and asphalt surfaces with vegetation or permeable pavement.

Forests benefit our health in so many more ways, from cooler air to better mental health. We need forests, and forests need us.

You can learn more about the connections between forests and health in WWF’s report, The Vitality of Forests.