Express News Service CHENNAI: Although Chennai’s daytime temperature breaches the 40 degree Celsius mark only for a few days in a year, the city is seen as one of the roughest places to live-in. The reason is humidity. Researchers, who are decoding this phenomenon, are calling it ‘Wet Bulb Temperatures’ which is also called mugginess, or wet heat, in local parlance. In hot conditions, humans cool themselves by sweating; but if the humidity is too high, sweating no longer works, and we risk dangerous overheating. At wet bulb temperatures (WBT) of 32 degrees Celsius, even fit, acclimatised people can’t work; and at WBT of 35 degrees, even fit, acclimatised people who sit in the shade die within about 6 hours. Climate change is making these WBTs increasingly likely. In the 2015 Indian Heatwave, WBT in Andhra Pradesh reached 30 degrees.