Why in news?
India is likely to experience an “above normal” monsoon rainfall between June and September this year. This was predicted by the India Meteorological Department (IMD) in its long-range forecast.
This is the first time in a decade that the IMD has predicted “above normal” rainfall at the first stage itself, nearly 45 days ahead of the beginning of the four-month monsoon season.
What’s in today’s article?
- El Nino and La Nina
- Indian Ocean Dipole (IOD)
- Prediction by IMD
- Factors indicating above normal rainfall
El Nino and La Nina
- El Nino:
- A warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean.
- It is associated with lower than normal monsoon rainfall in India.
- La Nina:
- A cooling of the ocean surface, or below-average SSTs, in the central and eastern tropical Pacific Ocean.
- It is associated with a comparatively better monsoon rainfall in India.
- Neutral:
- Neither El Nino nor La Nina.
- Often tropical Pacific SSTs are generally close to average.
Indian Ocean Dipole (IOD)
- The Indian Ocean Dipole (IOD) is defined by the difference in sea surface temperature between two areas (or poles, hence a dipole) – a western pole in the Arabian Sea (western Indian Ocean) and an eastern pole in the eastern Indian Ocean south of Indonesia.
- In scientific terms, the IOD is a coupled ocean and atmosphere phenomenon, similar to ENSO but in the equatorial Indian Ocean.
- A ‘positive IOD’ — or simply ‘IOD’ — is associated with cooler than normal sea-surface temperatures in the eastern equatorial Indian Ocean and warmer than normal sea-surface temperatures in the western tropical Indian Ocean.
- The opposite phenomenon is called a ‘negative IOD’, and is characterised by warmer than normal SSTs in the eastern equatorial Indian Ocean and cooler than normal SSTs in the western tropical Indian Ocean.
- The IOD was identified as an independent system only in 1999.
Prediction by IMD
- Above normal rainfall in 2024
- The country as a whole is expected to get 106% of long period average (LPA) rainfall.
- All forecasts are percentages of LPA. LPA is the average rainfall received in the past 50 years (currently, the average of 1971-2020 period).
- The rainfall between 96 per cent and 104 per cent of this 50-year average is considered normal; less than 90 per cent is considered deficient; 90-95 per cent is below normal; and 105-110 per cent is above normal.
- Nearly the entire country, except some pockets in the northwest, east and northeast, was likely to get good rainfall.
- India’s normal rainfall
- India, as a whole, normally receives 870 mm of rainfall during the monsoon season.
Factors indicating above normal rainfall
- Forecast of ‘good rainfall’ is attributed to weakening of El Nino, eventual development of the La Nina conditions during the second half of the season (Aug-Sep) and a positive Indian Ocean Dipole (IOD).
