El Niño – La Niña – ENSO

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Impact of El Niño

Generally, El Nino and the Indian Monsoon rains are inversely related. Trade winds coming from South America normally blow westward towards Asia during Southwest Monsoon. Warming of the Pacific Ocean results in weakening of these winds. Therefore, moisture and heat content gets limited and results in reduction and uneven distribution of rainfall across the Indian sub-continent.

The most prominent droughts in India, six of them, since 1871 have been El Nino triggered droughts, including the recent ones that occurred in 2002 and 2009. Nevertheless, it is important to note that all El Nino years do not lead to drought in India. The year 1997-98 is a stark reminder as it was a strong El Nino year but that did not cause drought in India, in fact, rainfall was in excess. On the other hand, a moderate El Nino in 2002 resulted in one of the worst droughts.

Going by historical data of 135 years from 1880 to 2014, about 90% of all evolving El Nino years have led to below normal rainfall and 65% of evolving El Nino years have brought droughts. From this fact, one thing is clear that El Nino years adversely affect the weather in India in terms of Monsoon rain, with very few exceptions. During an El Nino year, the rainfall is generally below the normal average, which has its negative bearing on crop production.

El Nino

El Niño means The Little Boy, or Christ Child in Spanish. El Niño was originally recognized by fishermen off the coast of South America in the 1600s, with the appearance of unusually warm water in the Pacific Ocean. The name was chosen based on the time of year (around December) during which these warm waters events tended to occur. The term El Niño refers to the large-scale ocean-atmosphere climate interaction linked to a periodic warming in sea surface temperatures across the central and east-central Equatorial Pacific.

Typical El Niño effects are likely to develop over North America during the upcoming winter season. Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest. 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.

El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which is characterized by unusually cold ocean temperatures in the Equatorial Pacific. El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. Among these consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia. In normal, non-El Niño conditions the trade winds blow to the west along the equator from South America towards Asia in the tropical Pacific Ocean. These winds pile up warm surface water off Asia, so that the sea surface is about 1/2 meter (1 1/2 feet) higher at Indonesia than at Ecuador in South America.

The sea surface temperature is about 8ºC (14ºF) warmer off the coast of Asia than in the eastern Pacific, due to an upwelling of cold water from deeper levels in the east Pacific. The cooler water off South America is nutrient-rich, supporting high levels of primary productivity, diverse marine ecosystems, and major fisheries. Clouds and rainfall are found in rising air over the warmest water near Asia, whereas the east Pacific is relatively dry.

During El Niño, the trade winds relax in the central and western Pacific leading to a flattening of the thermocline (blue band) due to a depression of the thermocline in the eastern Pacific, and an elevation of the thermocline in the west. The weakening of easterly tradewinds during El Niño is evident. Rainfall follows the warm water eastward, with associated flooding in Peru and drought in Indonesia and Australia. The eastward displacement of the atmospheric heat source overlaying the warmest water results in large changes in the global atmospheric circulation, which in turn force changes in weather in regions far removed from the tropical Pacific.

La Niña

La Niña means The Little Girl in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or simply “a cold event.” 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. La Niña is sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO. 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

ENSO

The El Niño-Southern Oscillation (ENSO) is a naturally occurring phenomenon that involves fluctuating ocean temperatures in the equatorial Pacific. The warmer waters essentially slosh, or oscillate, back and forth across the Pacific, much like water in a bath tub. For North America and much of the globe, the phenomenon is known as a dominant force causing variations in regional climate patterns. The pattern generally fluctuates between two states: warmer than normal central and eastern equatorial Pacific SSTs (El Niño) and cooler than normal central and eastern equatorial Pacific SSTs (La Niña).

Impact of El Niño and La Nina on Indian Weather

There are a number of climatic phenomena which affect. namely the Indian Ocean dipole, El nino, La nina, Equatorial Indian Ocean Oscillation (EQUINOO) etc. These phenomena affect the temperature distribution over the oceans and thus affecting the direction and intensity of flow of the moisture laden winds.

When the rainfall for the monsoon season of June to September for the country as a whole is within 10% of its long period average, it is categorised as a normal monsoon. When the monsoon rainfall deficiency exceeds 10%, it is categorised as an all-India drought year.

  1. In India, almost 50% of the area under cultivation is rain-fed. Indian agriculture is thus heavily dependent on the climate of India: a favorable southwest summer monsoon is critical in securing water for irrigating Indian crops. So, a significant reduction in total rain fall results in a drought like situation.
  2. Drought in India has resulted in tens of millions of deaths over the course of the 18th, 19th, and 20th centuries.
  3. In some parts of India, the failure of the monsoons result in water shortages, resulting in below-average crop yields. This is particularly true of major drought-prone regions such as southern and eastern Maharashtra, northern Karnataka, Andhra Pradesh, Odisha, Gujarat, and Rajasthan.
  4. Shortages in food supply then result in spike in food prices all across the country pushing inflation up. High food inflation eats into other sectors too such as food processing sector. This pushes the RBI and the government to adopt a more cautious approach to monetary and fiscal policy respectively.

 

Difference between El Nino and La Nina

El Nino and La Nina are caused by the sea-surface temperatures in the tropical part of the Pacific Ocean interacting with the atmosphere. The cycle of the water temperature changing from warm to cold usually occurs every three to four years. This is known as oscillation. In the Northern Hemisphere, the peak season for El Nino and La Nina is during the winter.

A large pool of warm water is located in the central and western part of the Pacific Ocean. Atmospheric conditions can increase the temperature of the surface water. As a result, this pool of warm water enlarges and shifts eastward to cover the tropics. El Nino also causes a decrease in the eastward flow of the trade winds. On the eastern side of the Pacific, parts of Australia, New Zealand, the Philippines and Indonesia experience drought conditions. The effect can spread as far as India. The opposite happens in North and South America where the general climatic conditions are wetter and warmer temperatures.

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