• India is likely to experience a warmer summer and more heat wave days this year with El Nino conditions predicted to continue at least until May, the India Meteorological Department (IMD) said.

• The country is likely to record above-normal rainfall in March (more than 117 per cent of the long-period average of 29.9 mm).

• India is likely to see above-normal maximum and minimum temperatures in most parts of the country in the March to May period.

• From March to May, the above-normal number of heat wave days is likely over most parts of the country except northeast India, the western Himalayan region, the southwest peninsula and the west coast.

• More heat wave days than normal are predicted over northeast peninsular India — Telangana, Andhra Pradesh and north interior Karnataka — and many parts of Maharashtra and Odisha.

• IMD said the prevailing El Nino conditions will continue through the summer season and neutral conditions are likely to develop thereafter.

• La Nina conditions are likely to set in by the second half of the monsoon season.

What is El Nino and La Nina?

• El Nino and La Nina events are a natural part of the global climate system. They occur when the Pacific Ocean and the atmosphere above it change from their neutral (‘normal’) state for several seasons.

• El Nino, which is the warming of the waters in the Pacific Ocean near South America, is generally associated with the weakening of monsoon winds and dry weather in India.

• La Nina, which is the opposite of El Nino, typically brings good rainfall during the monsoon season.

• These changes in the Pacific Ocean and its overlying atmosphere occur in a cycle known as the El Nino–Southern Oscillation (ENSO). 

• The term ‘El Nino’ translates from Spanish as ‘the boy-child’. Peruvian fishermen originally used the term to describe the appearance, around Christmas, of a warm ocean current off the South American coast. It is now the commonly accepted term to describe the warming of the central and eastern tropical Pacific Ocean. ‘La Nina’ translates as ‘girl-child’ and is the opposite ENSO phase to El Nino.

What is a heat wave?

• Higher daily peak temperatures and longer, more intense heat waves are becoming increasingly frequent globally due to climate change. India too is feeling the impact of climate change in terms of increased instances of heat waves which are more intense in nature with each passing year, and have a devastating impact on human health thereby increasing the number of heat wave casualties.

• Heat waves do not fetch as much public attention as more dramatic disasters such as earthquakes and floods, but until more recently they were taking a substantial toll of lives in India.

• A heat wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season. 

• Heat waves typically occur between March and June, and in some rare cases even extend till July. 

• The extreme temperatures and resultant atmospheric conditions adversely affect people as they cause physiological stress, sometimes resulting in death.

The IMD has given the following criteria for heat waves:

i) Heat wave need not be considered till maximum temperature of a station reaches at least 40°C for plains and at least 30°C for hilly regions.

ii) When normal maximum temperature of a station is less than or equal to 40°C heat wave departure from normal is 5°C to 6°C severe heat wave departure from normal is 7°C or more.

iii) When normal maximum temperature of a station is more than 40°C heat wave departure from normal is 4°C to 5°C severe heat wave departure from normal is 6°C or more.

iv) When actual maximum temperature remains 45°C or more irrespective of normal maximum temperature, heat waves should be declared. 

• The health impact of heat waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke.

What is heat index?

The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature.

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