폭염의 시대, 그늘권 확보 위해 ‘숲 지붕’을 늘려라

Global concerns over summer heatwaves are leading to discussions about the need to expand "tree canopies" or "urban forest cover" to protect public health. In New York City, an aggressive campaign to expand tree canopies is underway, backed by research showing its benefits. Tree canopies are formed by the leaves and branches of trees, creating shade on rooftops and streets.

They are the most active areas for photosynthesis and transpiration, forming the core of a tree's shade. This concept gained international attention when New York Mayor Cory Booker announced in April 2021 that the city aims to increase its tree canopy from 23.4% to 30% by 2040. NYC is focusing on three key initiatives: preserving existing tree canopy, planting more trees, and managing the city's urban forest.

South Korea is also beginning to recognize the importance of tree canopies. Seoul City announced on July 19 that it will incorporate "shade walking rights" as a basic element of its urban policy, allowing pedestrians to walk safely and comfortably in the shade. The plan includes wide sidewalks with large trees and row upon row of street trees in areas with sufficient space.

However, unlike New York, South Korea does not have specific targets for increasing tree canopies. Currently, there are no relevant statistics in South Korea. Perhaps the most prominent concept currently attracting attention for securing people's right to shade is tree canopies. While traditional green spaces consist of land covered by trees, grass, and soil, tree canopies refer to the area of land shaded by a tree's leaves and branches.

For instance, a 100㎡ park has a 100㎡ green area, but only a fraction of that is tree canopy. On the other hand, a shaded sidewalk lined with well-maintained trees may not be considered green space, but it can have a very large tree canopy. Tree canopies also change with the seasons. They are most extensive in summer and narrowest in winter.

Professor Hong Heekyung from Bupjeon University points out that while cities have traditionally prioritized green spaces and worked to increase green area ratios, during current climate crises, it is transpiration (the cooling effect of tree canopies) that is more crucial. New York's Mayor Booker has been promoting tree canopy planning for years.

Hong Heekyung from Bupjeon University says, "New York has been using tree canopy as a benchmark for years and has been focusing on it as the indicator for urban forest expansion." The reason tree canopies are gaining attention is because they can have a significant impact during summer heatwaves. According to data from the Forest Service in May, sidewalks with trees are about 3 degrees Celsius cooler than those without trees, with surface temperatures dropping by up to 10-25 degrees.

Seoul Environmental Union's expert member, Min Ju, explains that tree leaves block solar radiation, reducing the amount of heat absorbed by sidewalks, walls, and streets, while tree roots absorb water and release it, removing heat from the surrounding air. Tree canopies also help reduce air pollution. In April 2022, the Forest Service reported that trees on streets can prevent the spread of exhaust particulate matter from cars and create wind tunnels, lowering air pollution levels.

A 2023 study by the Korea-USA Tree Planting Symposium, presented by Kim Seonhee of the Life-Quality City Forest Research Center, found that sidewalks with trees had reductions of over 30% in fine particulate matter (PM2.5) and 15% in ultrafine particulate matter (PM1). Tree canopies also contribute to reducing mortality rates. A 2026 study by Northwestern University's Harrison Garretson and colleagues published in the journal "Geohelth" found a correlation between increased tree canopy cover and reduced mortality rates in diseases such as cardiovascular, mental health, musculoskeletal, and respiratory issues.

The study also noted that a 30% increase in tree canopy could lower the average city temperature by 0.4-5.9 degrees Celsius and reduce heat-related deaths by up to 40%. One common point highlighted by Garretson's research and New York City's approach is the importance of preserving existing tree canopies. New York City considers preserving existing tree canopies as one of its three main strategies.

However, South Korea's reality is quite different. Instead of focusing on preserving existing tree canopies, current practices include systematic pruning of trees, "beak pruning" of trees, removal of mature trees, and mass replanting during urban development projects, all of which destroy existing tree canopies. Hong Heekyung from Bupjeon University emphasizes that to increase tree canopies in South Korean cities, we must first establish tree canopy as a key indicator.

Currently, there are no statistics on tree canopies in South Korea. University officials also stress the need to preserve existing tree canopies during pruning and replacement, as well as to manage tree canopies in public streets and private residential areas.