What are El Nino and La Nina? Will they have any impacts on our coast?

By Dr. Anita George

With the latest global weather forecasts indicate a possible El Niño this year, India’s agrarian economy is likely to be affected.

The same is the case with the fisheries sector as the rising temperature, triggered by El Nino, is also expected to adversely impact the availability of fish stocks in the Arabian Sea.

As El Nino is characterised by a warming of surface temperatures in the Pacific Ocean, it may affect the South-west (June to September) monsoon in India.

According to the US National Oceanic and Atmospheric Administration, there is an 80 per cent chance that El Nino will prevail in March-May, decreasing to 60 per cent during the June-August period.

“The chance of El Nino developing in 2019 has increased to approximately 70 per cent, around triple the normal likelihood,” the Australian Bureau of Meteorology said, upgrading its outlook to ‘alert’ from ‘watch’ mode.

In this circumstances, we are looking into the scientific aspects of this particular weather phenomenon.

El Niño (pronounces as ‘el neen-yo’, ‘The Little Boy’, or ‘Christ Child’) and La Niña (pro. ‘La neen-ya’, ‘The Little Girl ‘) are Spanish words.

El Niño (the warm phase) and La Niña (the cold phase) are opposite stages of the El Niño-Southern Oscillation (ENSO) cycle which is a scientific term to describe the fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific.

These deviations from normal surface temperatures can have large-scale impacts not only on ocean processes but also on global weather and climate. El Niño and La Niña episodes typically last nine to 12 months, but some prolonged events may last for years. While their frequency can be quite irregular, El Niño and La Niña events occur on average every two to seven years. Typically, El Niño occurs more frequently than La Niña. They often begin to form between June and August, reach peak strength between Dec and April and then decay between May and July of the following year.

This abnormal warming of water in the central and eastern tropical Pacific Ocean every 3-5 years can last up to 18 months. Due to warmer oceans, the air gets lots of moisture due to evaporation on the way. This warm moist air rises to high levels of the atmosphere in the western part of the Pacific Ocean and causes rainfall in Indonesia, eastern and northern Australia including India.

A part of the air moves towards the eastern Pacific Ocean in the upper atmosphere and descends over the eastern Pacific Ocean, helps to sustain the pressure and again moves towards the western Pacific Ocean. This way we have a complete circulation of air between the eastern and western Pacific Ocean (Walker Circulation).

Sometimes, due to an abnormal warming of water in the central and eastern tropical Pacific Ocean, the high-pressure area in the eastern Pacific Ocean weakens or reverses its direction. Thus causing less rainfall in Indonesia, Australia, India and many other locations, whereas places near S. America will get heavy rainfall during this period.

The atmospheric pressure in the eastern Pacific Ocean is measured at Tahiti and in the western Pacific Ocean at Darwin, Australia. This situation reverses during El Nino years and this phenomenon is called Southern Oscillation (together called ENSO).

The rise of warm air finally results in its cooling in the upper atmosphere. The presence of El Niño can significantly influence weather patterns, ocean conditions, and marine fisheries across large portions of the globe for an extended period of time.

The effect an El Nino has on India is probabilistic in nature. There are 40 per cent chances that it can bring drought situation in India.

La Niña episodes represent periods of below-average sea surface temperatures across the east-central Equatorial Pacific. Global climate La Niña impacts tend to be opposite those of El Niño impacts.

In the tropics, ocean temperature variations in La Niña also tend to be opposite those of El Niño. During a La Niña year, winter temperatures are warmer than
normal in the Southeast and cooler than normal in the Northwest.

Generally, the fish catch will be lower than normal in South America during El Nino years, where warm water persists, and deepens, and cold upwelling, nutrient-rich water (which is present during normal years) fails to reach the surface and the marine life migrates north to south, following colder water.

Temperatures in Australia and southeast Asia run hotter than average. El Nino- caused drought can be widespread affecting southern Africa, India, southeast Asia,
Australia, the Pacific islands and Canadian waters. Generally, there will be more tropical storms.

Indian ocean towards Africa are unusually warm and the water towards Indonesia is extremely cool, they form a positive dipole and a vice versa phenomenon results in a
negative dipole.

The Indian monsoon, besides India also affects other regions of south and southeast Asia and Australia is the most monetarily important because of its serious influence on the economy of India and neighbouring countries.

During ENSO, the temperatures may go up to 45 deg. C. while the Indian Ocean is much cooler to equalize air pressure. Consequently, the warm air over the land rises and cooler moisture-bearing air blows in from the sea, bringing heavy rains to the region.

Starting with the coastline (Kerala), as the land cools in the downpour, the centre of heating and upward-convection slowly moves farther inland (usually Karnataka
receives the rains a week later). As long as the land remains relatively warmer, this monsoon circulation continues and moves northwards.

During winter (Sep onwards), the ocean is warmer than the land, the land having cooled sufficiently in the monsoon rains, so the cold air pulsates out of Asia to replace the warm air rising above the oceans. This brings us the North-east monsoon.

In other words, the cold air moving towards the ocean carries some moisture, giving us the rain.
A study from 1871-2005 by Krishnakumar et al. 2008 on the trends and variability in northeast monsoon rainfall over Kerala in the Journal of Agrometeorology says:
• There were 27 El Nino and 18 La Nina episodes
• There were 21 deficit rainfall years but only 4 belonged to El Nino years.
• There were 15 cases of normal monsoon years when El Nino occurred.
• Only 3 out of 25 excess rainfall were La Nina years
• There were 13 cases of normal NE monsoon years when La Nina occurred
• Examination of El Nino & La Nina in Kerala suggested that the majority of these events were associated with normal monsoon years
• Thus El Nino and La Nina events had weak teleconnection with excess/deficit northeast monsoon rainfall over Kerala.

What we can expect this year?
There is a negative IOD in the Indian Ocean and so we can expect a weak monsoon. Since the majority of our agriculture depends on monsoons, this will have an effect and can lead to food inflation???

Best is to save fish: especially oil sardines (extract oil – omega 3 fatty acids); dry fish, and prepare yourself, in case of the worst situation. Hope we will pass through easily…

Let’s have a ‘Great Wet Hope’ and ‘Less Impact of the Little Boy’

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