Number theory: How have El Nino and delayed onset affected monsoon in the past

An analysis of the 19 El Niño years shows that there was a deficit in monsoon compared to the 1961-2010 Long Period Average in 15 of them.

The India Meteorological Department (IMD) considers June 1 as the normal date of the onset of monsoon in India. This is the date on which monsoon rains have arrived on the Indian mainland (on the coast of Kerala) on average in the past. This year, monsoon rains have not started on the Kerala coast even on June 6. Can a delayed onset create a deficit in monsoon? This question is especially important this year because forecasts expect monsoon months to be affected by El Niño, a warming of the tropical Pacific Ocean that decreases monsoon rains. It could, though a HT analysis suggests that the relation between monsoon onset, El Niño, and monsoon performance, is not straightforward. Here are three charts that explain this.

This year, monsoon rains have not started on the Kerala coast even on June 6.(HT Photo/Sanchit Khanna)