Do April conditions in the Pacific Ocean point to a decisive El Nino this year?

When does an El Nino (warming of the east and equatorial Pacific) create widespread rain deficit over India during the monsoon?

K Srikanth, Chennai-based blogger and weather enthusiast, has found from a study that between 1950 and 2012, five years have seen 50 per cent or more meteorological divisions suffer deficit rainfall.

“If one observes the pattern, these years have shown either of the two following characteristics,” Srikanth told BusinessLine.

Firstly, a strong El Nino carried over from the previous year and devolving into a “neutral state” in the Pacific by the time the monsoon starts here. Secondly, a strong El Nino condition evolving from April onwards right in time for the onset of the monsoon (from April-May-June quarter), as it appears could be the case this year.

So, does history signal potential in so far as this year’s monsoon concerned?

“If one observes the long-term data where a strong Pacific event has either evolved or devolved during the monsoon, the probability of more meteorological divisions suffering deficit rainfall is higher,” says Srikanth.

Current conditions in the equatorial and east Pacific represent what he sees is threshold of a strong El Nino.

Madhusoodanan MS, specialist in atmospheric sciences and a fellow with TERI, concurs with the view that April conditions go to reflect what the state of the Pacific waters would be two months hence.

“By all accounts, the Pacific is priming for a strong El Nino,” he told BusinessLine . But what impact it would have on the monsoon is something that bears watching.

He cited the example of 1997, a strong El Nino year that witnessed sustained warming of the Pacific form April to November but largely spared the monsoon due to the favourable conditions in the Indian Ocean (positive Indian Ocean Dipole).

But a survey of international weather models did not suggest that the Indian Ocean was evolving in this manner just yet.

An earlier study by Srikanth had suggested that the impact of El Nino varies across various meteorological subdivisions with the Gangetic Plains profoundly impacted concurrently.

The current one tried to understand the impact of the period of El Nino and the rainfall status of the monsoon.

The January-February-March quarter of 2015 has seen a threshold situation continue from the previous year, Srikanth says.

The objective of the study was to find how the monsoon fared across select meteorological divisions when similar conditions existed in the past.

The period of study extended from 1950 to 2012. Met subdivisions include Kerala, Coastal Karnataka, Konkan-Goa, Odisha, Chhatisgarh, Jharkhand, Bihar, west Uttar Pradesh, east Uttar Pradesh, Gangetic West Bengal, Sub-Himalayan West Bengal, Assam-Meghalaya,and Nagaland-Manipur-Mizoram-

Tripura.

The year 1972 saw a marginal El Nino continue right through the monsoon season.

Interestingly, this year also saw only one meteorological division, sub-Himalayan West Bengal, face deficit rainfall, Srikanth says.

International weather models have assessed that there is 70 per cent chance of an El Nino establishing in the east and equatorial Pacific from next month.

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