Climate Change

How a possible El Nino can lead to failed monsoon in India?

Usually an El Nino event peaks during the winter season but the current event seems to be developing quite rapidly

Published: Thursday 18 May 2023

The southwest monsoon season is set to begin over Kerala by June 4, 2023 — three days later than usual, according to the latest IMD predictions. The weather agency also gave a model error of around four days, which means that the onset can be as late as June 8.

But it's not just that the monsoons have been delayed; several experts now predict that the upcoming southwest monsoon season may be shortened with a skewed distribution of rainfall over various regions. And this has everything to do with the spectre of an El Nino event looming on the equatorial Pacific Ocean.

So, how can a possible El Nino lead to failed rains in parts of India? There is more than an 80% chance of the development of an El Niño event in the equatorial Pacific Ocean in the May-June-July period. This chance increases to almost 90% for the June-July-August period. According to the National Oceanic and Atmospheric Administration (NOAA) of the United States

This development of an El Niño may coincide with the onset of the southwest monsoon season, which is the primary rainfall season in India. 60% of the El Niño years between 1951 and 2022 have witnessed below-normal or deficient rainfall during the monsoon season. India has also experienced droughts in many of these years.

According to data from IMD, the strength of an El Niño–Southern Oscillation event is measured by the Ocean Nino Index (ONI). When the index is between 0.5 and 0.9, it is classified as a weak El Nino event. When the index crosses 1.5, the event is strong and it is very strong when the index is above 1.9. Many ENSO models are predicting an ONI of more than 1.5 for the current El Nino event, Some models are even predicting an ONI of more than two.

According to the National Oceanic and Atmospheric Administration (NOAA) of the United States. This will have a tremendous impact on the rainfall distribution in India as the country receives 70% of its annual rainfall from June to September. In 2015, when the El Niño event was at its peak, India received only 86% of its normal monsoon rainfall and the year was officially a drought year for the country.

“Usually an El Nino event peaks during the winter season but the current event seems to be developing quite rapidly. The fact that there is going to be a delay in the onset of the monsoon season is indicative of this impact. Further, there may be widespread regional deficits in rainfall across the country” Roxy Mathew Koll, Climate scientist, Indian Institute of Tropical Meteorology (IITM), Pune.

There is also another situation at play now. According to the latest reports, cyclone Fabien has formed to the south of the equator, which is slowly chugging along and may take a week or more to cross over to land. This happens when the onset of the monsoon season is delayed or weak, which creates atmospheric and oceanic conditions conducive for cyclone formation, which will further pull away the winds and affect the monsoon season.

“The cyclone is seriously affecting the monsoonal circulation; especially the eastward moisture transport to the north of the equator. We need to watch out for it to see how it will affect the trough over the Andaman Nicobar and the Bay.” - Raghu Murtugudde. The Bay of Bengal has already experienced Cyclone Mocha in the second week of May 2023, which grew to become a super cyclone and made landfall along the Myanmar coast.

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