What is a heat wave and how is it measured? Heat Wave is measured differently in different countries and regions. There are many such points in India on the basis of which it is decided whether there is a heat wave in an area or not. If the temperature exceeds the normal 6.2 degrees, then a severe heat wave is declared. This year many states of the country have become core heat wave zones. Notably, in the last 100 years, the average annual temperature of India has increased by 0.62 degree Celsius. Watch this video.