New Delhi, May 24 -- Heatwaves have painted a grim picture in parts of India: Over 300 suspected heatstroke cases in Andhra Pradesh in nearly three months; 16 heatstroke deaths in Telangana; exhausted pigeons dropping unconscious from the sky, dehydrated eagles being picked up from roadsides; quintals of fish dying in Delhi lake.

What makes heatwaves deadly? How much heat can the human body endure? When does heatstroke happen? Here, we explain:

The India Meteorological Department (IMD) defines a heat wave as a period of unusually high temperatures as compared to what is normally expected over a region. It can lead to physiological stress and sometimes may cause death.

While the temperatures at which heat waves are declared differ from ...