El Nino-Southern Oscillation and its impacts over India

According to researchers, El Nino-Southern Oscillation (ENSO) is an irregularly periodic variation in wind and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics.

Climate in India

The climate of India comprises a wide range of weather conditions across a vast geographic scale and varied topography, making generalizations difficult. India hosts six major climatic subtypes, ranging from arid desert in the west, alpine tundra and glaciers in the north, and humid tropical regions supporting rainforests in the southwest and the island territories. Many regions have starkly different microclimates. Adding to these various local climates are four pronounced seasons: Winter (December, January, February), summer (March to May), Monsoon (June to September) and a post monsoon period (October to November).

India’s geography is climatically pivotal: the Thar Desert in the northwest and the Himalayas in the north work in tandem to affect a culturally and economically important monsoon regime. As Earth’s highest and most massive mountain range, the Himalayas bar the influx of frigid winds from the icy Tibetan Plateau and northerly Central Asia. Most of North India is thus kept warm or is only mildly chilly or cold during winter; the same thermal dam keeps most regions in India hot in summer.

While India’s local topography strongly shapes its climate, a weather pattern that arises on the other side of the planet off the coast of South America has such reach that its impact can at time be felt in the weather pattern of India. The El Nino weather phenomena is gaining strength. Later global forecasts indicate potentially affecting the south west from June to September monsoon of India. El Nino, characterized by warming of surface temperatures in the Pacific Ocean, is associated with lower than normal monsoon rainfall in India.

El Nino-Southern Oscillation

The El Nino-Southern Oscillation (ENSO) is an irregular cycle of change in wind and sea surface temperatures over the tropical eastern Pacific Ocean, affecting the climate of much of the tropics and subtropics^[1]. The warming phase of the sea temperature is known as El Nino and the cooling phase as La Nina. This sea temperature oscillation is accompanied by an oscillation in the weather patterns in the tropical western Pacific.

El Nino and La Nina events can last several years each and their effects vary in intensity. ENSO is known to strongly influence the rain in many countries in South America and East Asia. Depending on the location, some of the conditions associated with El Nino include: hot weather and droughts, forest and bush wildfires, heavy rain and subsequent flooding, tropical cyclone activity, typhoons and landslides. Developing countries dependent upon agriculture and fishing, particularly those bordering the Pacific Ocean, are the most affected by ENSO.

El Nino events are thought to have been occurring for thousands of years. For example, it is thought that El Nino affected the ancient Moche civilization in modern-day Peru, who sacrificed humans in order to try to prevent rain. It is thought that there has been at least 30 El Nino events since 1900, with the 1982 – 83, 1997 – 98, and 2015 – 16 events among the strongest on record.

And India is also significantly affected by ENSO^[2]. There is scientific evidence that shows that ENSO modulates Indian monsoon, with less than normal rain during El Nino phases and more than normal rain during La Nina phases.

Changes in the ENSO-Monsoon system

The monsoon influences environmental conditions in much of Asia, hence impacting most of the densely populated region of our planet. Differential heating of the north Indian Ocean and the north west Pacific Ocean and of the Indian landmasses, causes the seasonal reversal of monsoon wind. In summer this wind blows from the oceans to India, getting huge amounts of moisture over the neighboring land. This ensuing heavy rainfall can have devastating consequences for human lives and living beings. Conversely, agriculture in India and Asia depends on the monsoon rain, and the amount of nutrients in ocean surface waters is influenced by the monsoon and is essential to the success of fisheries. And El Nino widely affects the monsoon system.
The variable nature of Indian summer monsoon rainfall has a proven impact on India’s socio-economic growth. The Indian summer monsoon prevails over the Indian region for four months from June to September, in which it varies significantly temporally and spatially. In an agricultural country like India, the extreme departure from normal seasonal rainfall seriously affects the agricultural output and thus the economy of the country. It has been established that Indian summer monsoon is a fully coupled land-atmosphere-ocean system and that it is linked to ocean temperature variability. Past studies have revealed that the interannual variability of the Indian summer monsoon rainfall is linked to the El Nino-Southern Oscillation phenomena directly.

El Nino has become stronger and its pattern has been changing^[3][4]. A 400 year long seasonal record of El Nino created by Australian scientists has revealed that a new type of El Nino has become more prevalent in the last three decades than at any time in the past four centuries in the central pacific, and traditional that El Nino events have become more intense and major. The trend of El Nino in the last four centuries shows a variation in El Nino type. There has been a simultaneous increase in Central Pacific events and a decrease in Eastern Pacific ones. Since the late 20th century, the most recent 30-year period includes fewer but more intense Eastern Pacific El Nino events. The trend shows that the stronger Eastern Pacific El Nino events like those that occurred in 1997 1998 and 2015-2016 have been growing in intensity.

Conclusion

In conclusion, the southern oscillation between complementary El Nino and La Nina states results from interactions between the tropical oceans and the atmosphere. The detailed properties of the oscillation depend on long-term average background conditions that change gradually with time. As those conditions change, with the monsoon being linked to El Nino-Southern Oscillation phenomena, summer temperatures over much of India may rise to as high as 45 degrees Celsius, while the Indian Ocean is much cooler. The warm air over the land rises with lower moisture bearing air blowing from the sea, though sometimes bringing heavy rain. This Indian monsoon model implies that El Nino years should be considered with different monsoon rainfalls, and El Nino-Southern Oscillation has a wide effect over the monsoon rains over Asia and India.