When does El Nino impact on Indian Monsoon?

There is a  lot of discussion on Impact of El Nino on Southwest Monsoon in India.  The entire Indian Agriculture eco system revolves around Southwest Monsoon.  Mr. Vinson Kurian of Business Line who covers weather extensively in the Agriculture & Commodity section in the paper has in his column talked about how the timing of El Nino impacts the performance of Southwest Monsoon.  This has been done based on a study done by COMK. The article can be accessed here  Business Line Article

So when does El Nino Impact on Indian Monsoon?

Through the earlier study we had suggested the impact of El Nino varies across various meteorological sub divisions of India with the Gangetic Plains profoundly impacted by El Nino type conditions under concurrent relationship.

The current study tries to understand the impact of Period of El Nino and the rainfall Status of Southwest Monsoon.  The JFM quarter of 2015 has seen a threshold ENSO situation continue from the previous year.  The objective of the study was to find how SWM fared across select meteorological divisions when similar conditions existed in the past.

Between 1950 & 2012 7 years have seen the ONI Index hover around the threshold level of 0.5C / 0.6 C.  Of these 7 years, 4 years have seen only 2 or lesser Meteorological division get less than 90% rainfall of the long term average.

Except for one year 1953 during all these years the ONI Index has either gone towards neutral during SWM or changed over to La Nina levels during SWM.  The year 1953 saw marginal El Nino continue right through the SWM season.  Interestingly this year also saw only one meteorological division, Sub-Himalayan West Bengal, face deficit rainfall. 

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So when does El Nino create widespread deficit seasons?

Between 1950 & 2012 of the years that have seen 50% or more meteorological divisions suffer deficit rainfall if one observes the pattern these years have shown either of the two following characteristics except for one year which was Enso Neutral.

  • A strong El Nino from the previous year that devolves into a ENSO neutral state by the time SWM season starts
  • Strong El Nino condition evolves from April onwards right in time for SWM Season (from AMJ quarter)

Does History indicate potential answers for this year’s SWM. If one observes the long term data whenever strong ENSO has either evolved or devolved during the SWM season the probability of more meteorological divisions suffering deficit rainfall is higher.  The current Nino 3.4 Index 0.98 C, the threshold of a Strong El Nino.

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We take this opportunity to thank Mr. Vinson Kurian for placing trust on us.

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