BANGKOK, THAILAND – A leading environmental and health scientist warned at the start of the hot season that people should not judge heat danger by air temperature alone but instead monitor the heat index more closely.
Scientist warns against relying on the thermometer
Environmental physician Dr Sonthi Kotchawat used Facebook to highlight that high air humidity could drive the perceived temperature sharply upwards, even when the thermometer still showed seemingly moderate values. He stressed that this gap between measured and perceived temperature could decide whether staying outdoors was still acceptable or already carried a high risk of heat-related illness.
What the body actually feels
According to his explanation, the heat index described the temperature the human body actually felt because it took into account both air temperature and relative humidity. This value indicated more precisely how strongly the cardiovascular system was strained and how likely it was that the body could no longer shed heat adequately.
Humidity pushes danger above 50°C
For the hot months from March to mid-May, Dr Sonthi pointed out that relative humidity in many regions averaged between 60 and 75 percent. Under such conditions, an air temperature of 36 degrees Celsius could result in a heat index above 50 degrees Celsius, which he classified as extremely dangerous.
Why sweating stops being enough
In the academic’s assessment, the body mainly cooled itself through sweating, but the effect depended crucially on air humidity. At low humidity, sweat could evaporate well and remove heat, while at high humidity evaporation slowed and dangerous heat built up inside the body.
Four official heat index risk levels
The commonly used guidance in the country divided the heat index into four rising risk zones, starting with 27 to 32 degrees as a level of special caution. This was followed by 32 to 41 degrees with heightened warning, 41 to 54 degrees as a danger zone and values above 54 degrees as extreme danger with a clearly elevated risk of heatstroke.
Advice for getting through the hot season
Dr Sonthi advised people to adjust their behaviour consistently when the heat index was high, including drinking 2 to 3 litres of water in small sips over the day, before feeling thirsty. He also recommended light-coloured, loose clothing, actively cooling the body in case of overheating and avoiding strenuous outdoor activities, especially between 11.00 a.m. and 3.00 p.m.