April 9, 2015 2:26:02 am
The first monsoon forecast is two weeks away, but Indian weather scientists are watching with some concern a developing ocean-atmospheric condition in the Pacific near the equator — El Nino.
El Nino, which describes a condition in which ocean in equatorial Pacific regions becomes unusually warm, is known to have an impact on the Indian monsoon, besides several other weather events worldwide. There is a strong correlation between an El Nino event and a poor monsoon.
The US National Oceanic and Atmospheric Administration (NOAA) announced last month that an El Nino condition was developing. Worryingly, it predicted there was a good chance it would last longer than usual, a rare phenomenon that sometimes is simplistically described as “double El Nino”.
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An advisory from the Climate Prediction Centre of NOAA on Monday says El Nino conditions were present, and “positive equatorial sea surface temperature anomalies” (a reference to ocean surface warming) were continuing across most of the Pacific Ocean. It also said that there was an “approximately 50-60 per cent chance” that El Nino conditions “will continue through the Northern Hemisphere summer” of 2015. That might not be good news for the Indian monsoon.
“In the past 65 years, there have been 19 El Nino events. The average duration of the El Nino during this period was 10 months. There were two long El Ninos. In 1986-87, the El Nino lasted for 19 months, and was associated with two consecutive droughts in 1986 and 1987. The other long El Nino was in 1968-69 and lasted for 18 months. It was associated with droughts in 1968 and 1969. So, long El Ninos can be a cause for concern in India,” J Srinivasan, chairman of the Divecha Centre for Climate Change at the Indian Institute of Science, Bangalore, said.
Exactly how long this year’s El Nino will be cannot be predicted at this time, he said.
The El Nino condition, which induces a sinking motion over India, hence preventing formation of deep clouds, is only one of several factors that influence the Indian monsoon. For this reason, and also because El Nino conditions become clearer in June, scientists were cautioning against jumping to conclusions about the monsoon as of now.
“It is a bit too early to predict what exactly will be the impact on the monsoon. As of now, we cannot even tell how the El Nino will finally develop. It will become clear only around June. It will all depend on how rapidly the Central Pacific warms up between now and June,” Srinivasan said.
D Sivananda Pai, head of the Long Range Forecasting division at the Pune office of India Meteorological Department, said El Nino conditions were evident last year as well, but had weakened subsequently, and had little impact on monsoon.
“This is not the right time to say anything definitive about the El Nino. Yes, the conditions are developing but a better picture emerges only in May and June,” Pai said. Srinivasan explained that more than the duration of an El Nino, it was its strength – the extent of temperature increase – that was important. And the strength would become clear only after the condition developed fully.
A rise in temperature of less than 1 degree Celsius does not significantly impact the monsoon. But sometimes, the temperature can rise by as much as 4 or 5 degrees Celsius.
The strongest El Nino year in the last few decades was in 1997. After that, 2002-2003 and 2009-10 were El Nino years. Both those years, 2002 and 2009, witnessed poor monsoon and resulted in widespread drought.
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