Heat Wave Conditions in India

During summer we quite often hear about heatwave conditions at various places in India. This article explains that under
what circumstances the heat waves are declared.

Different countries define heatwave as abnormal rise of temperature for a particular number of days. While in India, India
Meteorological Department has defined it as a rise in temperature by atleast 5º C from its normal temperature on a particular day.

There are two regions where heatwave 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 heatwave the temperature of a place should reach the temperature by 40º C for plains and at least 30º C for Hilly regions.

Below are the 3 conditions for declaring Heatwave and Severe Heatwave 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 the actual maximum temperature remains 45ºC or more irrespective of normal maximum temperature, heatwave should be
declared.