Nature's air conditioner: How urban forests are cooling Korea's heat waves

Visitors stroll through the bamboo forest in Gwangju, South Jeolla Province, July 20. Yonhap

As record heat waves continue to bake concrete jungles across the globe, city planners looking for thermal relief may find their best tool planted right outside their front doors. According to new research from Korea’s National Institute of Forest Science, urban forests serve as powerful, natural air conditioners, slashing daytime temperatures by nearly 2 degrees Celsius compared to heavily built-up city centers.

The findings, released Monday by the forest research agency, draw on continuous temperature and humidity tracking across various urban environments in Seoul. The data reveals that city forests provide a consistent cooling effect, lowering temperatures by up to 1.8 degrees Celsius at the peak of midday heat.

However, not all green spaces cool equally. Researchers discovered that broadleaf and mixed forests — composed of both deciduous and coniferous trees — offered the most dramatic heat reduction, cooling surrounding areas by 1.5 to 1.8 degrees Celsius. Coniferous stands were slightly less effective, lowering temperatures by about 1.2 degrees Celsius.

Scientists attribute this microclimate mitigation to two key ecological processes: dense canopy shading and evapotranspiration. During summer months, thick, leafy canopies form a protective shield against direct solar radiation. At the same time, trees release water vapor into the atmosphere through their leaves, drawing latent heat from the surrounding air and creating a localized chilling effect.

The cooling benefits do not vanish when the sun sets.

The study found that urban forests maintain temperatures 1.3 to 1.6 degrees Celsius lower than dense urban centers overnight, offering crucial relief from tropical nights — periods where nighttime temperatures fail to drop below comfortable levels. Unlike asphalt and concrete, which store heat during the day and radiate it outward after dark, forest ecosystems release far less stored thermal energy, helping regulate citywide microclimates around the clock.

"Urban forests are critical green infrastructure protecting residents from intense summer heat waves, with multilayered broadleaf and mixed forests demonstrating exceptional cooling performance," said Choi Su-min, a researcher at the institute's Urban Forest Research Center. "Moving forward, urban planners must actively incorporate these specific vegetation structures when designing city parks and green zones."

As climate change accelerates the frequency and intensity of summer heat, the Urban Forest Research Center said the study underscores a growing consensus among urban planners: investing in diverse, multilayered forest canopies is no longer merely an aesthetic amenity, but an essential public health strategy to keep modern cities livable.

This article was published with the assistance of generative AI and edited by The Korea Times.