Simply cool!: The best air conditioner works without electricity

A third of Switzerland is covered by forests – 1.31 million hectares, an area roughly larger than the cantons of Bern and Graubünden combined. Even when it’s hot, it stays relatively cool there. Why actually?

Ueli Meier (62), both Foresters of the Canton of Basel, says this is not primarily because of the shade the canopy provides. He lives in Baselland, right next to the forest, which he describes as a great privilege. Among other things, the forest works like an air conditioner and actively contributes to the cooling of the environment.

This is because the water stored in the leaves starts to evaporate when hot, Meier says. If the leaves are exposed to strong sunlight, they begin to sweat. “Sweat” evaporates. This process requires heat that it extracts from the environment. “It causes cooling under the leaves. On hot summer days, the inside of the forest can be up to four degrees cooler than the outside.”

A cool breeze rises

Meier says the cooling effect cannot be felt only in the forest. The cold air that develops under the canopy sinks to the forest floor because it is heavier than the warm air. It’s escaping from the edge of the forest because it can’t accumulate there, Meier says. “People in the area feel it in the form of a cool breeze in the afternoon.”

Meier says the cooling radius of the forest varies greatly. The denser the shadow of the leaves in the forest, the stronger the effect of evaporative cooling and cooling wind. “If you need to cool off on hot days, it’s best to go to the woods whenever possible.”