The key to cooling down urban heat islands might be found in the countryside, according to a new study by the University of Surrey and Southeast University in China.

Using 20 years of data, researchers discovered that nearby rural areas can help lower city temperatures. The biggest cooling effect happens when the rural area around a city is at least half the city’s diameter.

A new focus

“We often focus on green spaces, wetlands, or waterways to cool cities,” the authors say. “But urban land is valuable and limited. Our study shows that how we use land outside a city can significantly impact temperatures within the city.”

The study offers specific advice: connecting rural land patches, planting more woodland around the city, and having fewer but larger lakes instead of many small ones helps reduce urban heat.

As warm air rises in a city, it creates low pressure near the ground, drawing in cooler air from surrounding rural areas. This process is influenced by the city’s size and the nature of the surrounding land.

Urban heat

To understand this better, scientists compared areas around 30 Chinese cities between 2000 and 2020. Satellite data showed ground temperatures and land use.

“We already suspected that belts of rural land around a city could help cool down the urban center,” the authors explain. “Now, thanks to our detailed analysis, we can say which forms of land use lead to the biggest effects.

“We hope planners and governments can use our findings to help urban communities become more resilient against rising global temperatures. Our findings show that if we want to cool our cities down, we need a joined-up approach between urban and rural planning.”