During summer we quite often hear about heat wave conditions at various places in India. This article explains that under
what circumstances the heat waves are declared.
Different countries defines heat wave as abnormal rise of temperature for a particular number of days. While in India, India
Meteorological Department has defined it as rise in temperature by atleast 5º C from its normal temperature on a particular day.
There are two regions where heat wave conditions criteria are defined. These regions are coastal areas and inland areas.
Coastal regions mostly have moderate climate and inland have extreme climate.
To declare a heat wave the temperature of a place should reach the temperature by 40º C for plains and at least 30º C for Hilly regions.
Below is the 3 conditions for declaring Heat wave and Severe Heat wave conditions in India:
a) When normal maximum temperature of a station is less than or equal to 40º C:
For Heat Wave – Departure from normal is 5º C to 6º C
For Severe Heat Wave – Departure from normal is 7º C or more
b) When normal maximum temperature of a station is more than 40º C
For Heat Wave – Departure from normal is 4º C to 5º C
For Severe Heat Wave – Departure from normal is 6º C or more
c) When actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heat wave should be