El-Nino and La-Nina for UPPSC Mains Exam

By Nitin Singhal|Updated : February 16th, 2021

Hello aspirants,

This article is about El-Nino, La-Nina & ENSO, which is one of the important article in UPPSC Mains GS Paper 1 Geography section. The aspirants can use this article for both revision and answer writing practise.

 El Nino

  • El Nino is a Spanish word which means 'The Little Boy'.
  • The occasional climatic change and development of warm ocean surface waters along the coast of Peru and Ecuador are called El Nino effect.
  • It was recognized first time by fishermen at the coast of South America during the 1600s.
  • In El Nino the trade winds which blows along the Equator from east to west weakened and created high air pressure in the Western Pacific ocean and low air pressure in the eastern pacific ocean. 
  • Due to this, the surface water moves towards the coast of northern South America. 
  • The central and east Pacific ocean warms up during six months and results in an El Nino effect. 
  • During El Nino, the warming of the central and east pacific ocean reduces the usual upwelling of cold water which ultimately reduces the nutrient content in that region.
  • The warmer waters of the East Pacific Ocean cause the winds in various regions to reverse. 
  • El Nino effect normally occurs around Christmas and lasts for a few weeks to a few months.
  • Sometimes it may last for much longer time periods depending on the warming of the waters. 
  • Such a warming environment for seven to nine months is known as El Nino "conditions", and when the duration is longer, it is classified as El Nino "episode".
  • Normally, the El Nino effect occurs more frequently than La Nina effects.

Causes of El Nino

  • El Nino occurs when there is some anomaly in the pattern of trade winds.
  • El Nino mainly causes when the westward-blowing trade winds along the Equator weaken and changes air pressure.
  • Due to changes in air pressure the warm surface water of the Pacific Ocean starts moving eastward toward the coast of Peru and Ecuador.
  • These warm waters in the central and eastern Pacific regions warm up the entire region, which results in an El Nino condition. 
  • Due to warm surface waters humidity increase which results in above-normal rainfall in South America, and droughts like a situation to Indonesia and Australia.

Effects of El Nino

  • El Nino affects global weather conditions. 
  • It increases eastern Pacific hurricanes and tropical storms. 
  • Unusual and heavy rainfall in the eastern pacific ocean and nearby countries like Peru, Ecuador and Chile.
  • It reduces the upwelling of cold water due to which upliftment of nutrients deposited at the bottom of the ocean decreases.
  • Due to this low upliftment of nutrients, the marine and sea birds industry get adverse effects.  
  • the drought-like situation caused by El Nino can be widespread, which may affect countries like southern Africa, Southeast Asia, Australia, India and the Pacific Islands. 
  • The farm-based countries get affected at the most.
  • The condition of El Nino increases the chances of vector born diseases in Central and South America.
  • It is responsible for coral bleaching.


  • La Nina is a Spanish word which means the Little Girl' or simply 'a cold event'.
  • In La Nina, the cold water of the Eastern Pacific Ocean gets colder than normal, which results in the accumulation of cold water in the central and eastern Pacific Ocean.
  • In La Nina, the reversal of trade winds does not take place. However, it causes very high pressure at the eastern equatorial Pacific Ocean.
  • After the El Nina effects, the weather conditions return back to normal, usually at a faster rate. 
  • One of the strongest La Nina effects occurs in 1988 in which the Atlantic Ocean has seen active hurricane seasons.
  • 'Mitch' was one of the strongest October hurricanes developed in the history of the last 100 years.

Causes of La-Nina

  • It mainly causes when easterly trade winds become much stronger.
  • Due to this, more warm water accumulates towards the western Pacific Ocean and cold water toward central and eastern Pacific Ocean. 
  • The strong easterly trade winds blow warm water towards the western Pacific Ocean due to which the eastern and central Pacific Ocean waters tend to be lower than the normal temperatures.
  • Many times the La Nina follows El Nino; however, they occur at irregular intervals of around 2-7 years.

Effects of La-Nina

  • It creates heavy monsoons throughout India and Southeast Asia.
  • It creates a drought-like situation in Peru and Ecuador. 
  • It causes wet and cool winters in southeastern Africa and wet weather condition in eastern Australia.
  • In the Southern United States, it creates winter draughts. 
  • It creates cold winter condition in the northwestern United States and western Canada.
  • It causes heavy floods in Australia.
  • It creates high temperatures in the regions of Western Pacific, Indian Ocean and off the coast of Somalia.
  • It causes heavy monsoon rains across India. 

Impact of La Nina and El Nino on India

  • India is a farm-based country, and around 50% of its area is under cultivation. Also, the Indian agricultural system is largely depended on the strength of monsoon and the quantity of precipitation. Hence La Nina condition is much favourable for Indian agriculture and economy at large.
  • In this way, a La Nina effect will create sufficient precipitation in India which will directly boost the farm produce. 
  • On the other hand, heavy rainfall sometimes creates floods in some areas, which affects the life of people and the economy adversely. 
  • The lager farm produces will enhance the economic growth of the country. 
  • However, the El Nino during winter season causes warm conditions over the Indian subcontinent and dry and deficient monsoon during summer.
  • Hence, it creates a draught like situation and affects agriculture.
  • The Crops like Paddy, Groundnut, Maize, Guar, Castor, Moong, Tur and Bajra suffers a lot due to El Nino conditions.

Major Difference between La Nina and El Nino

  • During El Nino, the trade winds blowing from east to west gets weakened. However, during La Nina, the trade winds blowing from east to west gets stronger.
  • During El Nino, the warm waters accumulate over the eastern Pacific Ocean. However, during La Nina, the warm water accumulates over the western Pacific Ocean.
  • The El Nino is ladened with high air surface pressure over the western Pacific. However, La Nina contains low air surface pressure over the eastern Pacific Ocean.
  • In El Nino, the wind speed is low. However, in La Nina, the wind speed is very high.
  • In El Nino, the strength of the Coriolis force decreases. However, in La Nina, the strength of the Coriolis force increases. 
  • El Nino creates heavy rainfall in the eastern pacific ocean and nearby countries like Peru, Ecuador and Chile. However, La Nino creates draught like condition over the eastern pacific ocean and in the nearby countries like Peru, Ecuador and Chile.


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