More than 1,800 people have died in one of the worst heat waves in India’s recent history. Temperatures nearing 50°C melted roads in New Delhi and scorched crops in the fields. It proved especially deadly in the southern states of Andhra Pradesh and Telangana, where at least 1,700 died in the past week.
May is consistently India’s hottest month, but, even so, temperatures shot far above normal. In the coastal region of Andhra Pradesh, daytime temperatures rose more than 7°C higher than average.
Aftab Ahmad, an internal medicine expert at the Apollo Health City, a hospital complex in Hyderabad, said there could be many reasons for the heavy death toll. “The prime among them is what is called climatic acclimatization,” he told media “This year the temperature changed suddenly. This disturbs the defence mechanisms of the body.”
India’s extreme weather serves as a stark reminder of how vulnerable the human body is to severe heat. Unable to adapt to sweltering conditions, people become susceptible to sunstroke and severe dehydration.
Claude Piantadosi director of the Duke Centre for Hyperbaric Medicine and Environmental Physiology in Durham, says human beings aren't built to spend long periods of time in temperatures that exceed the body’s own temperature of about 37 degrees.
Normally, the body stays cool by shedding unused energy in the form of heat dissipating by conduction, or the transfer of heat energy to the skin's surface, and then by convection, the transfer of heat energy to the air. The hotter it gets, the more difficult it becomes to shed that heat. At temperatures topping 100 degrees, the system reverses and heat flows from the environment into the body,
At that point, humans depend on a second cooling mechanism: perspiration. Sweat heats up and is transformed into water vapour, which removes heat from the body and reduces the internal core temperature. But high humidity defeats the system, because sweat won't evaporate when the air is already saturated with moisture. "The combination of heat and high humidity is really quite deadly," Piantadosi says. "It defeats our heat dissipation mechanism."