[Science Scope] What Korea Should Truly Fear: The Hot and Humid Heatwave

Even Lower Temperatures Than Europe, Yet More Deadly
The “Water-Laden Heat” Driven by the North Pacific High

If the heatwave that swept through France was a parched and “dry heat,” the summer in Korea is fundamentally different. It is not only the temperature that rises; the humidity soars as well. Even at the same 35 degrees Celsius, the air feels suffocating and the body tires easily. Recently, climate scientists and health experts have been focusing on the dangers of hot and humid heatwaves, as they significantly undermine the body’s ability to lower its temperature, making them far more deadly than high temperatures alone.

A farmer harvesting crops in the heatwave, cooling off by drinking water. Photo by Yonhap News Agency

The human body sweats when it is hot, and this sweat cools the body as it evaporates. However, when humidity is high, the air is already saturated with moisture, which means sweat does not evaporate easily. As a result, the body’s heat cannot escape, making the perceived temperature much higher than the actual maximum, and sharply increasing the risk of heat-related illnesses. The heatwave of the Korean summer cannot be explained by thermometer readings alone.

Humidity: More Dangerous Than Temperature... Warnings from WBGT and Wet-Bulb Temperature

This is why there are more cases of evaluating the risk of heatwaves not just by the maximum temperature, but by “Wet-Bulb Globe Temperature (WBGT)” or “wet-bulb temperature.” WBGT is an index that combines temperature, humidity, radiant heat, and wind to represent the actual heat load experienced by humans. Because it directly indicates how much the body is exposed to heat, organizations such as the Fédération Internationale de Football Association (FIFA) and the International Olympic Committee (IOC) use it as a standard for match suspensions (cooling breaks) to protect athletes’ safety.

When describing the limits of human endurance, “wet-bulb temperature” (the temperature reflecting the effect of moisture in the air) is frequently cited. Theoretically, if the wet-bulb temperature reaches 35 degrees Celsius, even healthy adults cannot regulate their body temperature through sweating and may face life-threatening situations within hours. Vulnerable groups such as the elderly and those with chronic illnesses may be at risk at much lower temperatures. Unlike the dry heat of Europe, which is bearable in the shade, Korea’s humid and windless “steaming heat” poses a different level of thermal stress on the body.

Lee Myung-In, head of the Heatwave Research Center at Ulsan National Institute of Science and Technology (UNIST) and professor of Urban and Environmental Engineering, warned, “Due to climate change, sea surface temperatures around the Korean Peninsula are rising rapidly, which means the risk of heatwaves with both high temperature and humidity will only increase in the future. As the background temperature rises, the intensity of heatwaves will inevitably increase, even under the same atmospheric pressure systems.”

‘Southerly Tropical Nights’: The Onset of a 24-Hour Disaster

This summer, Korea is particularly likely to be exposed to hot and humid heatwaves. The Korea Meteorological Administration expects that sea surface temperatures in the North Pacific will remain higher than average, leading to a strong development of the North Pacific High, especially over the eastern part of Korea.

Because the North Pacific High rotates clockwise, the Korean Peninsula will be continuously affected by warm and humid air blowing in from the southern seas along its periphery. Woo Jin-gyu, spokesperson for the Korea Meteorological Administration, explained, “If the North Pacific High is positioned to the east of Korea, the inflow of humid warm air along its edge will bring many days with both high temperatures and high humidity to the peninsula.”

The problem is that high humidity does not end with the heat of the day. Water vapor in the air acts as a lid, trapping heat at the surface overnight. When tropical nights persist for long periods, the body loses the opportunity to recover from fatigue and is left defenseless against heat-related illnesses.

Heatwaves can no longer be described by the simple figure of the maximum temperature. The real danger does not lie in how high the temperature gets, but whether people can release internal heat from their bodies. In the era of climate change, what Korea truly needs to be wary of is not just “higher temperatures.” The “hot and humid steam box” that traps body heat is the new climate disaster our society must prepare for going forward.

This content was produced with the assistance of AI translation services.