El Nino and South West Monsoon in India – A Study

Among weather enthusiasts one of the most debated topics is whether El Nino affects Indian Monsoon or not? There are a lot of studies that have been conducted over time to prove the arguments on both sides.  Sky Met Weather has recently in association with ASSOCHAM released a study that says Devolving El Nino may not impact this year’s South West Monsoon drastically and are expecting a normal monsoon this year.  IMD has indicated a 50% probability of El Nino happening in time this year to have an impact of South West Monsoon.

In this context COMK thought it would be interesting to run a comparison analysis on the relationship between ENSO and SWM Rainfall to find if there exists a coefficient relationship between the two.  For this study the monthly SST Anomaly data of Nino3.4 region and the SWM average monthly rainfall data for the West Peninsular India region, a region that derives majority of its annual precipitation during the SWM season was chosen.  The overall performance of SWM for the season closely mirrors the SWM season for this region hence is a key indicator of how good or bad Monsoon was for that particular year.

The period of study is during the years 1982 to 2006 a total of 25 years. The West Peninsular India precipitation data has been obtained from here http://www.tropmet.res.in/static_page.php?page_id=52 while the SST Indices have been obtained from here http://www.cpc.noaa.gov/data/indices/wksst8110.for

The following are the findings of the study. (Please click on the individual images for high res version of the data)

  • 4 of the 8 drought years have seen El Nino showing up during the South West Monsoon period, 3 of the years had strong El Nino and in the other year it appeared during September effectively confirming 50% of the drought years have been brought by El Nino


  • Of the 5 Excess years only one year had El Nino associated with it, though even in that case El Nino came up only from September. It certainly appears El Nino conditions do not result in excess monsoon years often


  • There exists a moderately strong negative relationship between the Nino 3.4 SST Anomaly and the precipitation pattern for West Peninsular India during South West Monsoon.


  • The precipitation for the months of July & September are impacted if there exists El Nino type conditions concurrently.
  • The month of September possibly has the highest impact if El Nino type conditions exists with lesser than average rainfall on more years than often in such cases.
  • When one runs an analysis of rainfall for the individual months when El Nino exists concurrently more often than not it has resulted in Deficit rainfall for that months.


With El Nino on the way and possibly a strong El Nino on the cards it appears the probability of a higher than average South West Monsoon for the year 2015 looks remote as things stand.