New Delhi : Indian Ocean Dipole (IOD) is an irregular climatic event that occurs in the Indian Ocean when the sea surface temperature between the eastern tropical Indian Ocean and western tropical Indian Ocean differs. The Indian Ocean Dipole is sometimes called India’s El-Nino and its impact can be seen in weather and climate patterns in India and as far as Indonesia, Australia, New Zealand and Africa.
This year Indian Ocean Dipole is a hot topic of discussion among the policy makers as a positive or neutral Indian Ocean Dipole Index (IOD Index) is likely to reduce El-Nino’s adverse impact on India’s south-west monsoon.
According to the latest official data, not only the onset of Monsoon has been delayed this year but it is nearly 23 percent deficient in comparison with the Long Period Average as defined by the country’s apex weather department.
What is the Indian Ocean Dipole?
When Indian Ocean Dipole climatic phenomenon occurs then the temperature of sea surface of eastern parts of Indian Ocean that is close to West Australia becomes colder than its long period average and alternately, the sea surface temperature of western part of Indian Ocean that is close to African continent becomes hotter than its long period average (LPA).
If the Indian Ocean Dipole is positive then it results in unusual climatic changes across several countries in the Indo-Pacific region and it is linked to droughts and wildfires in Australia and more rains in Africa and India. This irregular climatic event is similar to El-Nino and La-Nino climatic events that occur in the Pacific Ocean but their impact is felt across several countries including India, Australia and USA.
What is El-Nino?
During normal weather conditions in the Pacific Ocean, winds blow west along the equator, taking warm water from South America towards Asia. In the process, the cold water rises from the deeper parts of the oceans to replace the warm water. Scientists refer to this process as ‘upwelling’. During this El-Nino phenomenon, these winds that blow towards the west become weaker. As a result, the warm water is pushed back east, toward the west coast of the Americas. This disturbance in the normal weather pattern has a significant impact on India’s south-west monsoon.
According to experts, El Niño lasts 9 to 12 months, but can sometimes last for years. El Niño and its opposite climate disturbance La Niña, occur every two to seven years, on average, but there is no regular schedule for these climatic disturbances. El-Nino in the Pacific Ocean is known to have caused droughts and deficient rains in India, severely affecting cereals and food grain production.
Interplay between IOD and El-Nino affects Monsoon
Although El-Nino and Indian Ocean Dipole climatic events occur thousands of miles apart from each other and they are not necessarily observed in the same year. However, whenever these two irregular climatic events occur at same time, then they are known to mitigate or aggravate their impact. For example, a positive Indian Ocean Dipole is known to mitigate the adverse impact of El-Nino on Indian monsoon rains.
A positive Indian Ocean Dipole means a warmer sea surface temperature in western tropical Indian Ocean that results in more precipitation in the Indian and African continents, thereby negating the adverse impact of El-Nino that is known to have caused droughts and deficient monsoon rains in India.
That is why Indian policy makers and farming sector experts are hoping that a positive Indian Ocean Dipole Index will negate the possibility of drought-like situation in the country. India’s Met Department’s prediction of a somewhat normal monsoon is based on the Indian Ocean Dipole (IOD) indicator being favourable to the country this year.
According to experts, India has received lower than long period average rainfall at times when El Nino was accompanied by neutral or negative Indian Ocean Dipole index.
What is the current state of Indian Ocean Dipole?
According to the latest data, the IOD is currently neutral. When the Indian Ocean Dipole Index is >0.4 then it is considered positive while on the other hand when the index is <-0.4 then it is considered negative and the values between these two ends are considered neutral. According to some experts, a positive IOD is likely to develop in the coming months, which will mitigate the adverse impact of El-Nino on India’s monsoon rains.
How does El-Nino affect Indian agriculture?
According to the data analysed by India Ratings and Research, a Fitch Group rating agency, ten years out of 33 years during 1990-2022 were classified as El Niño years with different levels of intensity. However, the country experienced rainfall deficiency of over 5% in 7 of these 10 years and only five of these seven years were classified as drought years. It means five of 10 El-Nino years in India led to a drought like situation.
According to experts, south-west monsoon rains in the country are a complex phenomenon and their performance is influenced by a number of factors which include the impact of El Niño or La-Nina in the Pacific Ocean, the state of the Indian Ocean Dipole, state of the Tropical Atlantic sea-surface temperature and Eurasian land heating. If the Indian Ocean Dipole value remains at or above the threshold of 0.4, it creates favourable conditions for the monsoon rainfall.
