When temperatures in a city located in a tropical country, such as our capital Hanoi, reach 40 degrees Celsius, residents feel extremely fatigued and easily exhausted. However, at the same temperature in a desert, people can endure it more comfortably. Why is that?
The northern region of our country is currently experiencing a widespread heatwave, with many areas facing intense heat. Tomorrow, June 13th, the highest temperature in Hanoi is expected to reach 37oC (air temperature), and the perceived temperature outdoors will soar to 46 – 47oC.
Such temperature levels in Southeast Asian countries are known to cause heat stress to the human body, which can be very dangerous, leading to heat exhaustion, heat stroke, cramps, etc. However, at the same temperature in a desert, the level of heat stress is not as severe as in tropical regions (like ours).
This is because heat stress is primarily caused by temperature, but also by other weather-related factors such as humidity, wind, and radiation.
Perceived temperature in several provinces in Northern Vietnam this afternoon, June 13. (Photo: Zoom Earth, OpenStreetMap).
Our bodies receive heat from the surrounding air, from the sun, or from internal processes such as digestion and exercise. To respond to this, our bodies must dissipate some of the heat. We lose some heat to the surrounding air and some through breathing. However, most heat is lost through sweating because when sweat on the skin’s surface evaporates, it takes energy away from the skin and the surrounding air.
Weather factors significantly affect all of these processes. For instance, high humidity decreases the evaporation rate of sweat from the skin.
Thus, high humidity makes heatwaves in Southeast Asia more dangerous, and Southeast Asia is known to be one of the most humid regions in the world.
Southeast Asia is a region with high humidity in the world. Humidity levels in several provinces in Northern Vietnam this morning, June 13. (Photo: Zoom Earth, OpenStreetMap).
However, even the level of heat stress has its limits. This means that when heat stress reaches a certain level, everyone—even those in good health and accustomed to hot weather—will become exhausted and uncomfortable, even with moderate activity. This threshold, in sunny conditions, is approximately 39oC with around 50% humidity. According to The Straits Times, this limit has been exceeded in some locations in Southeast Asia during recent heatwaves.
In contrast, similar high temperatures in countries with lower humidity, far from the tropics, result in lower heat stress and danger levels. For example, the UK has recorded temperatures as high as 40oC, but with humidity around 20%, the heat stress was not severe, and residents did not find it unbearable.
Similar temperatures can have very different effects on people in different regions of the world. (Illustration: iStock).
Therefore, on hot and humid days, people always need to remember to drink more water than usual and avoid prolonged outdoor activities, as when the weather approaches the physiological limits of the human body, even completely healthy individuals staying outside for too long can be at great risk.
