Evolving El Nino meets threshold value, raises alarm

Are we staring at an El Nino year in 2014-15? Well, it seems so as the evolving El Nino has met the threshold mark in its first season. However, there are still four more seasons - of three months each - to go in which the El Nino has to maintain above sea surface temperatures (SST), the prime criteria to declare an El Nino. So folks, relax there is still a long way to go before the panic button is pressed.

Evolving El Nino

The phenomenon of abnormal warming of surface ocean waters in the equatorial Pacific, which occurs every three to seven years, is termed as El Nino. El Nino leads to warming of this sea surface temperature (SST) anomaly above 0.5°C.

The Oceanic Nino Index (ONI) is based on SST departures from average and El Nino is generally declared when ONI is greater than or equal to 0.5°C for overlapping 3 months. And according to the Japan Meteorological Agency, positive equatorial SST anomalies have formed across most parts of the Pacific Ocean. The September, November and December (SON) threshold in the Nino 3.4 region is 0.5°C, which needs to be construed as an evolving El Nino and not a full-fledged system at this stage.

For a full-fledged El Nino to happen, the threshold value needs to be met for 5 consecutive seasons (SON, OND, NDJ, DJF and JFM), which means seven months. Currently the September, October and November (SON) threshold is met, while the OND threshold period looks positive. But we need to wait for the NDJ, DJF and JFM average, before declaring 2014-15 as an El Nino year.

Equatorial Pacific is divided into four parts Nino 3, Nino 4, Nino 3.4, Nino 1+ 2, for Meteorological analysis. Nino 3.4 is the region of El Nino. Here’s a look at the surface temperatures since November-

Impact on India

Though, at the moment the El Nino is amplifying and the October, November and December (OND) threshold period is meeting the criteria, it looks to weaken in the coming seasons of NDJ, DJF and JFM, collapsing in the last leg.

If the El Nino does meet the criteria of sea surface temperature (SST) anomaly of above 0.5°C throughout the monsoon seasons of India then we will observe below average rain in the country. And if it fails to maintain the required threshold during these months than we can expect a normal Monsoon in India, which looks very much probable.

Chances of successive drought years in India is very rare. Going by the historical data, consecutive drought years have been observed only once in last 40 years, in 1986 and 1987. India has already gone through drought in Monsoon 2014, therefore chances of 2015 becoming a drought year is remote. Also with the possible collapsing of this El Nino, we can expect  normal monsoon rainfall.