Issue

Context

• The India Meteorological Department (IMD) has indicated an increased probability of El Nino conditions from February 2019, probably resulting in above-normal summer temperatures.
• Experts have cautioned that an El Nino event occurring early next year could have some impact on the monsoon of 2019 for India.

Background

• According to the scientists, since October 2018 sea surface temperatures across the east-central tropical Pacific have reached weak El Nino levels.
• However, the atmosphere has failed to respond to this additional warmth, and hence has not yet coupled to the ocean in a manner typically associated with an El Nino event. For example, the upper level winds, cloud and sea level pressure patterns in the tropical Pacific do not yet reflect El Nino features.
• Since October, trade winds in the eastern tropical Pacific Ocean have briefly weakened to El Nino levels, but have not been consistently weaker than normal.

About

What are El Nino and La Nina events?

• El Nino is the name given to a slight warming of the surface waters of the Pacific. It is opposite of La Nina, which is a cooling. As the ocean is one of the biggest influences in our weather, both of the phenomena have a dramatic effect on the weather around the globe.
• El Nino was discovered far earlier than La Nino, as it had a direct impact on the Peruvian fishermen. They noticed that every three to seven years, in the months of December and January, there would be virtually no fish in the seas. As it was noticed around Christmas time, they named this phenomenon El Nino (Spanish for ‘the baby boy’).
• The strength of the El Nino conditions and its impacts on the weather can vary dramatically.
• Partly due to its earlier discovery, much more is known and understood about El Nino than La Nina.

El Nino-Southern Oscillation (ENSO)

• The El Nino-Southern Oscillation (ENSO) is an irregularly periodical variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean. It has a major influence on weather patterns over many parts of the world. The warming phase, which is thought to impact India’s southwest monsoon, is known as El Nino, while the cooling phase is La Nina.

Analysis

 What happens ‘normally’ at a time when there is no El Nino or La Nina?

• The warmest part of the Pacific Ocean is the region near the equator. Due to the spinning of the earth, the prevailing winds flow from east to west. This pushes the warm waters westwards, towards Indonesia.
• In the east, around the coast of South America, cool waters would normally well up. These waters are rich in nutrients and fish, and provide plenty of food for the Peruvian Fisherman.
  
  
  

  During El Nino and La Nina

• During an El Nino event, the prevailing winds across the Pacific weaken, and sometimes they can even reverse and blow the other way. This allows some of the warmer waters to move eastwards, away from Indonesia and towards South America.
• La Nina has some different effects; for instance, as the waters near the coast of South America are warmer than usual, it makes sense that the weather in the region is also warmer than usual. This will increase evaporation and therefore the region will also see more rain than in a typical year. It also is intuitive that because the warmer waters are moving away from Indonesia, the weather here is drier than usual.
• However, there are far more wider-reaching impacts of El Nino that are not at all instinctive and affect the weather across many parts of the globe. For example, El Nino usually decreases the hurricane activity in the Atlantic.
  • The temperature of waters below the surface of the tropical Pacific, from the west-central Pacific eastward and extending to several hundred meters below the surface, have been above average since April 2018, and more strongly so since October.
  • This deeper warm water now extends to the surface, and is likely to sustain surface waters at El Nino-level temperatures in the coming months. El Nino-level sea surface temperatures currently observed could persist through the remainder of 2018 and into the first quarter of 2019.
  • Propensity towards a deficient monsoon is more during El Nino conditions. But, El Nino is only one of the parameters governing Indian monsoon variability.The strongest El Nino event that has ever been recorded occurred in 1997- 1998. Its impact was felt in many parts of the world. Droughts hit Indonesia and other islands in the western Pacific, triggering uncontrollable forest fires. Peru suffered deadly flooding. Record-breaking rainfall hit the US state of California, causing mudslides and flooding. Kenya too, was hit by severe flooding.
    
    

El Nino 2018

• The temperature of waters below the surface of the tropical Pacific, from the west-central Pacific eastward and extending to several hundred meters below the surface, have been above average since April 2018, and more strongly so since October.
• This deeper warm water now extends to the surface, and is likely to sustain surface waters at El Nino-level temperatures in the coming months. El Nino-level sea surface temperatures currently observed could persist through the remainder of 2018 and into the first quarter of 2019.
• Propensity towards a deficient monsoon is more during El Nino conditions. But, El Nino is only one of the parameters governing Indian monsoon variability.

IMD prediction for 2019

• A recent probability forecast for El Nino and La Nina (ENSO) by the IMD indicated maximum probability for ENSO neutral conditions (neither an El Nino event nor a La Nina event) from October to February next year. Thereafter, increased probability for El Nino conditions is seen from February to July.
• As on October 2018, international models are showing Nino 3.4 index temperature values crossing the El Nino threshold level of 0.5°C. While IMD model forecasts are showing the index value to be slightly less than 0.5°C, other international forecasting centres are indicating that by the end of this year or early next year, weak or moderate El Nino might occur and may continue up to next spring i.e. March or April 2019.
• While the India Meteorological Department (IMD) officials stressed that it might be too early to say, experts have cautioned that an El Nino event occurring early next year could have some impact on the monsoon of 2019. However some other experts view that El Nino might start weakening by spring next year and might not impact monsoon, except the beginning of the season.
• An event is considered to be weak El Nino if the sea surface temperatures over the equatorial Pacific Ocean increase by more than 0.5°C above normal.
• There could also be a chance of an increase in summer temperatures next year because of the El Nino event. Scientists are of the view that whenever there is an El Nino during summer; temperatures tend to rise, with increased chances of stronger or more severe heat waves.
• The observed sea surface temperature anomalies are showing warming over the central and eastern Pacific, indicating an imminent El Nino event. If an El Nino develops in February next year, it may exist for a long time or several months, which may not be too favourable for monsoon 2019.

Conclusion

• La Nina and El Nino conditions are detected by looking at data from various sources, including satellites and buoys. However, it’s very difficult to forecast the conditions of the ocean more than three months in advance.
• With impacts on such an enormous scale, improved forecasts of these events would be invaluable. Countries would be able to prepare for flooding or droughts and this could undoubtedly save many lives.

Learning Aid

Practice Question:

IMD has predicted an El Nino event from February 2019 and warmer summer for India. What do understand by El Nino? Discuss its impact over Indian Monsoons.