El Niño and the Indian Monsoon: Why a Strong El Niño Does Not Always Mean a Poor Monsoon
Since 1950, seven Indian monsoon seasons have taken place during a moderate or strong El Niño (a warming of the central and eastern Pacific Ocean).
In five of these seven years, including 2026, monsoon rainfall was at least 10% below the long-term average. The India Meteorological Department (IMD) calls this level "deficient".
Two years did not follow the pattern. The 2023 season was "below normal" (94% of the average), not deficient. The 1997 season, during one of the strongest El Niños of the 20th century, ended with nearly normal rain, even though the IMD had expected a shortfall of about 8%.
The 2026 southwest monsoon (June to September) ended about 12.6% below the long period average of about 87 cm. East and Northeast India had their driest monsoon since records began in 1901.
The 2026 El Niño is still growing and is expected to peak around December 2026. Scientists point out that other factors, such as the Indian Ocean Dipole, can weaken or strengthen El Niño's effect on India. So El Niño raises the risk of a poor monsoon, but it does not decide the result alone.
Long Period Average (LPA) and IMD Rainfall Categories
The Long Period Average, or LPA, is the average monsoon rainfall that India received over a long base period of many years. The India Meteorological Department (IMD) uses it as the "yardstick" to judge each year's monsoon. For the whole country, the LPA of the June to September monsoon is about 87 cm (868.6 mm), based on the 50 years from 1971 to 2020. When you read "the monsoon was 87% of LPA" or "rainfall was 12% deficient", the comparison is always with this average.
The 2026 monsoon ended at about 87% of the 87 cm LPA, which puts it in the "deficient" band (below 90%). The 2023 El Niño season, at 94% of LPA, was only "below normal", and 1997 was near normal. These categories are how scientists can say that five of the seven strong El Niño monsoons since 1950 were "deficient", while two were not.
El Niño–Southern Oscillation (ENSO)
ENSO is a natural climate swing in the tropical Pacific Ocean. Every few years, the sea surface in the central and eastern Pacific becomes unusually warm (El Niño) or unusually cool (La Niña), and the winds and air pressure above the ocean change with it. Because the Pacific is so large, this swing changes rainfall and temperature across the world, including India. During El Niño, the area of rising air and heavy rain moves east, towards the central Pacific, and the air over India tends to sink more, which usually weakens the monsoon.
The 2026 El Niño is one of the strongest on record and the monsoon ended deficient, as in most strong El Niño years. But the 1997 and 2023 seasons show that El Niño is only one push on the monsoon. Its effect can be weakened by other ocean and air patterns, so forecasters cannot read the monsoon from the Pacific alone.
Indian Ocean Dipole (IOD)
The Indian Ocean Dipole, or IOD, is a swing in sea surface temperature between the western and eastern parts of the tropical Indian Ocean. In a positive IOD, the western Indian Ocean (near Africa and the Arabian Sea) is warmer than usual and the eastern side (near Indonesia) is cooler. This pulls more moist air and rain towards India and East Africa. A positive IOD can therefore partly cancel the drying effect of El Niño on the Indian monsoon, while a negative IOD can make things worse.
The 1997 season is the best example of why a strong El Niño does not guarantee a poor monsoon: the positive IOD that year worked against El Niño and India's rain stayed close to normal. In 2026, a positive IOD was expected to give only partial and late help, which was not enough to stop the season from ending deficient.
- Moderate or strong El Niño monsoons since 1950: 7; of these, 5 (including 2026) were "deficient" (at least 10% below average)
- 2023 monsoon: 94% of LPA ("below normal"); 1997: nearly normal despite an IMD forecast of about an 8% shortfall
- 2026 southwest monsoon: about 759.4 mm against an LPA of 868.6 mm, a shortfall of about 12.6% (87% of LPA), the lowest since 2015
- East and Northeast India: driest southwest monsoon since records began in 1901; Meghalaya about 60% below normal
- IMD 2026 forecasts: 92% of LPA (13 April, first stage) and 90% of LPA with ±4% error (29 May, second stage)
- All-India LPA: about 87 cm (1971 to 2020 base); "deficient" season means less than 90% of LPA
- 2026 El Niño expected to peak around December 2026; WMO forecast about +3.7°C anomaly for October to December 2026