- The India Meteorological Department (IMD) has retained its outlook of an ‘above normal’ monsoon this year.
- Quantitatively, the southwest monsoon seasonal rainfall over the country as a whole is likely to be 106% of the long-period average (LPA) with a model error of ± 4%.
| Long Period AverageThe IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period of 50 years.The IMD’s recent prediction was based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average. A 50-year LPA covers large variations in either direction caused by freak years of unusually high or low rainfall. |
The monsoon ‘core zone’, which encompasses most of central India and is critical for the Kharif crop, and southern India is expected to see ‘above normal’ rainfall.
- Cyclone Remal had given a push to the eastern branch of the approaching monsoon system. It is uncertain if the monsoon would begin in Eastern India before Kerala —an extremely unusual, but not unprecedented phenomenon.
- India’s strong monsoon rainfall is predicated on El Niño conditions withering away to ‘neutral’ conditions and the onset of La Niña conditions during the later part of the monsoon season.
- At present, neutral Indian Ocean Dipole [IOD] conditions are prevailing over the Indian Ocean. The latest forecasts from many global climate models indicate positive IOD conditions are likely to develop during the monsoon season.
- El Nino, La Nina and IOD conditions refer to temperatures in the Central Pacific, and the eastern and western halves of the Indian Ocean respectively.
| ENSO and Indian Ocean Dipole In a normal year, the eastern side of the Pacific Ocean, near the northwestern coast of South America, is cooler than the western side near the islands of the Philippines and Indonesia. This happens because the prevailing wind systems that move from east to west sweep the warmer surface waters towards the Indonesian coast. The relatively cooler waters from below come up to replace the displaced water. An El Nino event is the result of a weakening of wind systems that leads to lesser displacement of warmer waters. This results in the eastern side of the Pacific becoming warmer than usual. During La Nina, the opposite happens.These conditions, called El Nino Southern Oscillation or ENSO, affect weather events worldwide. Over India, the El Nino has the impact of suppressing monsoon rainfall.IOD, sometimes referred to as the Indian Nino, is a similar phenomenon, playing out in the relatively smaller area of the Indian Ocean.IOD is said to be positive when the western side of the Indian Ocean, near the Somalia coast, becomes warmer than the eastern Indian Ocean. It is negative when the western Indian Ocean is cooler. |
La Nina conditions coupled with a favourable IOD spell good rains for India.
Dig Deeper: Read about other factors that influence the Indian Monsoon.
