La Nina conditions likely to prevail up to end of year, not likely to impact Indian monsoon

La Nina conditions prevailing over the equatorial Pacific region are likely to continue up to the end of the year, the India Meteorological Department (IMD) said on Thursday even as experts said it may not be a cause of worry for the Indian monsoon.

The latest forecast by the Monsoon Mission Coupled Forecast System (MMCFS) of the IMD said that the Indian Ocean Dipole (IOD) conditions, which is at present neutral with negative DMI index over the Indian Ocean, is likely to develop negative conditions during the upcoming season.

DMI Index or Dipole Mode Index (DMI) means the difference between sea surface temperature (SST) anomalies in two regions of the tropical Indian Ocean.

“Other climate models are also indicating enhanced probability for La Nina conditions during the upcoming season,” said the IMD forecast.

La Nina refers to large-scale cooling of ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall.

It usually has the opposite impacts on weather and climate as that of El Nino, which is the warm phase of the El Nino Southern Oscillation (ENSO).

ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought. For India, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above-average rains, and colder winters.

Earlier on June 10, the World Meteorological Organization (WMO) had said that there is high probability that the ongoing protracted La Nina event – which has affected temperature and precipitation patterns and exacerbated drought and flooding in different parts of the world – will continue until at least August and possibly to the northern hemisphere fall and start of winter.

“Some long-lead predictions even suggest that it might persist into 2023. If so, it would only be the third ‘triple-dip La Nina’ (three consecutive northern hemisphere winters of La Nina conditions) since 1950,” the WMO had said.

“By now, in terms of time, 3/8 th of the monsoon season is over. The country as a whole has received 3/8 th of the normal seasonal rainfall. This is an optimal situation. I don’t think there is any cause for concern as of now, notwithstanding how ENSO or IOD evolve in the coming months. We are approaching August. By September, the monsoon starts withdrawing. I don’t see any serious threat at this point of time,” said Ranjan R. Kelkar, former IMD Director General (Meteorology).

As compared to June, warming of Sea Surface Temperature (SST) anomalies were observed over the equatorial eastern Pacific Ocean and warming of SST anomalies were observed over the north Pacific Ocean.

“In the north Indian Ocean, weak positive SST anomalies were observed over most parts of the Arabian Sea and Bay of Bengal. A weak negative SST anomaly was observed over western equatorial Indian Ocean. Also, there were positive SST anomalies observed over most parts of the south Indian Ocean. As compared to the last month, cooling of SST anomalies were observed over north Arabian Sea and most parts of south Indian Ocean,” the IMD said.

The three-month season average SST anomaly forecast indicates that negative SST anomalies are likely over most parts of the central and eastern equatorial Pacific Ocean until the end of the year.

“The probability forecast for ENSO indicates the 45 per cent probability for La Nina conditions during the JAS (July, August, September) season, which is higher than its climatological probability. However, the probability increases to 58 per cent by the end of OND (October, November, December) season,” the forecast said.

Almost echoing what Kelkar said, former Secretary in the Ministry of Earth Sciences, Madhavan Nair Rajeevan, said, “La Nina cold SST anomalies are likely to persist at least till September, which should help Indian monsoon. Negative IOD prevailing now is likely to weaken in the next few months. Put together, we should expect a normal monsoon in the next two-three months. At present, we should not worry about the monsoon.”

Stating that other climate models are also indicating enhanced probability for La Nina conditions during the upcoming season, a senior meteorologist said, “We (IMD) are closely monitoring ENSO conditions and monthly updates are provided as per the observed changes in the Pacific Ocean SSTs. Western Indian Ocean is likely to remain slightly cooler than normal and Eastern Indian Ocean likely to remain slightly warmer than normal for the next couple of seasons.”

Incidentally, the Intergovernmental Panel on Climate Change (IPCC) reports has warned that El Nino and La Nina events have been more frequent and stronger since 1950. However, the IPCC has not specified if it was because of natural variability or climate change.




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