El Nino arises in the eastern Pacific, along the coast of South America. El Nino is a climate phenomenon that occurs when a vast pool of water in the western tropical Pacific Ocean becomes abnormally warm i.e. 0.5 degree Celsius more than the average. Under normal conditions, the warm water and the rains it drives are in the eastern Pacific.

Its most direct impacts are droughts in normally damp places in the western Pacific, such as parts of Indonesia and Australia, while normally drier places like the west coast of South America suffer floods. But the changes affect the global atmospheric circulation and can weaken the Indian monsoon and bring rains to the western US.

An El Niño is officially declared if the temperature of the western tropical Pacific rises 0.5C above the long-term average.
El Niño events occur every five years or so and peak in December, but the first, and potentially greatest, human impacts are felt in India.

During the evolution of a typical El Niño, as the western side of tropical Pacific cools and eastern part warms, trade winds, which blow from east to west over that ocean, weaken considerably and sometimes even reverse direction. This shift in wind pattern aids the growth of the El Niño.

There could be several factors influencing the interplay between an El Nino and the monsoon. For one thing, which part of the Pacific warms has an impact on the monsoon.

Besides, what happens in the Indian Ocean also shapes the course of the monsoon.

Indian Ocean Dipole (IOD)

During a ‘positive IOD’, the eastern equatorial Indian Ocean off Sumatra in Indonesia becomes colder than normal while the western tropical part of the ocean near the African coast becomes unusually warm. Such an event has been found to be beneficial for the monsoon. A positive IOD had facilitated normal or excess rainfall over India in 1983, 1994 and 1997 despite an El Nino in those years.

A ‘negative IOD,’ when temperatures at either end of the Indian Ocean swing in the opposite direction, hampers the monsoon. But during years such as 1992, a negative IOD and El Nino had cooperatively produced deficit rainfall.
Equatorial Indian Ocean Oscillation (EQUINOO)

During the positive phase of the (EQUINOO), there is enhanced cloud formation and rainfall in western part of the equatorial ocean near the African coast while such activity is suppressed near Sumatra.

This phase is associated with good rains over India. Its negative phase, when cloud formation and rainfall flares up near Indonesia, retards rains over India.

How does El Nino impact India?

• Less rainfall – drought – poor irrigation for farmers – impacts agriculture.
• Fragile food supply- food inflation.
• Global impact on food supplies with lower yield for corn, wheat and rice – soyabean harvest tend to rise.
• Soaring prices of vegetables – a deterioration in kharif cropping>/li>
• Less water supply – shortage of power and electricity in the affected region.
• Affects the commodity prices and the government– not good for the economy.

Some facts:

The worst El Nino that India ever faced was in the year 2009.

There has been a rainfall shortage of around 42% in India uptil June, 2014. States like Gujarat and Rajasthan have over 80 per cent of deficient rain.

India is expected to be the first to suffer, with weaker monsoon rains, followed by further scorching droughts in Australia and collapsing fisheries off South America. But some regions could benefit, in particular the U.S., where El Niño is seen as the “great wet hope”, bringing rains that could break the searing drought in the west.

Rainfall data for 126 years indicates that the odds of a drought jump to over 40 per cent when there is an El Nino.

In 1997, the eastern Pacific had become exceptionally warm, thereby limiting the atmospheric circulation changes that adversely affected the monsoon. It was when the sea surface temperature anomalies were highest in the central Pacific that an El Nino had drought-producing effects over India.

Central Pacific El Ninos had appeared in 2002 as well as in 2004 and 2009, with all three years ending in drought.

Latest prediction for 2014 suggests that this year, India will experience a negative IOD.

EQUINOO and IOD go in step during strong positive IOD events, such as in 1994 and 1997.

The severe drought of 2002 occurred when a moderate El Nino as well as strong negative EQUINOO together took a toll on the monsoon; that year, the IOD was slightly positive.

References:

http://www.thehindu.com/sci-tech/science/el-ninos-complex-link-to-the-monsoon/article6127021.ece
http://www.thehindu.com/sci-tech/science/could-this-years-el-nio-be-like-the-2009-one/article6170122.ece
http://www.thehindu.com/news/national/june-national-rain-average-42-deficient/article6159385.ece?ref=relatedNews
http://www.theguardian.com/environment/2014/jun/11/-sp-el-nino-weather-2014
http://articles.economictimes.indiatimes.com/2014-06-22/news/50772456_1_indian-monsoon-eastern-pacific-high-pressure