A relentless heat wave with temperatures approaching 40 degrees Celsius has persisted across South Korea, prompting President Lee Jae Myung to describe the situation as "effectively a national disaster situation." Speaking during a recent meeting with senior secretaries and aides, Lee stressed that the government must maximize the level, scope, and speed of its policy response to protect people's lives and ensure public safety. The extreme temperatures are part of a broader pattern of intensifying summer heat waves that have strained infrastructure and public health systems across Asia this year, raising urgent questions about how dense cities can adapt to a warming climate.

Amid the extreme heat, research continues to illuminate the vital role that urban trees play in cooling cities and protecting public health. A recent study from the United States found that mortality rates in large cities may decline as tree-shaded area increases, while a domestic analysis of Seoul's 25 districts revealed a similar pattern: neighborhoods with more trees experience lower surface temperatures. The findings add to a growing body of evidence that unequal tree coverage is not merely an aesthetic concern but a public health disparity with measurable consequences.

U.S. Study Links Tree Canopy Expansion to Lower Mortality

A research team at the Northwestern University Feinberg School of Medicine tracked changes in Chicago, Illinois, from 2011 to 2021, examining data on tree canopy coverage, peak summer temperatures, and the number of deaths.

The study found that increases in annual tree canopy coverage were associated with lower mortality. A 1 percent increase in shaded area was linked to an approximately 9.8 percent decrease in overall mortality.

Broken down by cause of death, a 1 percent increase in tree canopy coverage was associated with a 9.2 percent reduction in cardiovascular disease mortality. The associations were even stronger for respiratory diseases, at 11.3 percent, and mental disorders, at 16.4 percent.

The researchers' simulations indicated that if Chicago planted an additional 14,000 trees each year, the proportion of shaded areas would rise by 0.03 percent, which was associated with preventing approximately 105 deaths annually. Conversely, in the hottest parts of Chicago, mortality rates rose sharply as tree coverage declined.

The researchers noted that "because this was an observational study rather than an experiment, it is difficult to establish a causal relationship." However, they explained that tree shade can significantly reduce urban temperatures, heat stress, and exposure to air pollution, while encouraging physical activity and improving stress levels and mental health.

Seoul's Tree Coverage Varies Sharply by District

A comparable pattern has been documented in Seoul. The National Institute of Forest Science, under the Korea Forest Service, recently analyzed the relationship between the proportion of urban forest coverage and summer surface temperatures across Seoul's 25 autonomous districts using satellite data.

The analysis found that areas where trees covered more than 30 percent of the district had lower average temperatures than areas with less tree coverage. The temperature difference became more pronounced as the proportion of land covered by trees increased.

According to the institute, Seoul has significant disparities among its districts in terms of urban forest coverage. Gangbuk District ranked among the highest, with trees covering 62.3 percent of its area, followed by Jongno District at 61.1 percent, Gwanak District at 57.4 percent, Eunpyeong District at 52.2 percent, and Dobong District at 51.3 percent. In these districts, trees cover more than half of the total area.

By contrast, Yeongdeungpo District had the lowest urban forest coverage at just 5.8 percent. Gangseo District and Seongdong District also barely exceeded 10 percent, at 10.2 percent and 10.8 percent, respectively. Such stark gaps mean that residents in less-canopied districts face measurably greater exposure to heat during dangerous heat waves, potentially widening health disparities between neighborhoods within the same city.

According to records from the Korea Meteorological Administration's Automatic Weather Station, a station in Nowon District recorded 40.2 degrees Celsius.

The Science of Urban Cooling

Trees absorb water through their roots and transport it to their leaves, where it is released into the atmosphere through evaporation. This process, known as transpiration, has a cooling effect on the surrounding environment. Because evaporation absorbs heat from the surrounding area, transpiration can help partially alleviate the urban heat island effect, a phenomenon in which dense concentrations of pavement, buildings, and other heat-absorbing surfaces raise city temperatures well above those of surrounding rural areas. Tree shade also helps block solar radiation.

"Not only large-scale urban forests but also a single tree or a small patch of forest can help mitigate the effects of heat waves," said Je Sun-mi of the National Institute of Forest Science's Urban Forest Research Center.

As cities worldwide grapple with more frequent and severe heat waves, urban forestry has gained attention as a relatively low-cost, scalable intervention. Seoul's district-level data suggests that targeting tree-planting efforts in the most canopy-poor neighborhoods could be one practical lever for reducing temperature gaps and protecting vulnerable residents.

This article from Kormedi.com, Korea's top health care and medical portal, is translated by a generative AI system and edited by The Korea Times.

Source: The Korea Times