La Niña may develop between Sept and Nov; likely to hamper post-monsoon season in India
There is a 60% chance of a weak La Niña event between September and November, according to the World Meteorological Organisation’s (WMO) update, and could result in lesser rainfall in the post-monsoon season in India.
“We have only one more month left for monsoon and this year monsoon is likely to be normal--finishing at 102% of the long-period average with an error margin of +/-4%. The impact of La Nina during the post-monsoon season is just the opposite of what it is during monsoon season. La Nina during the monsoon season is associated with above-average rains. But during the post-monsoon season, if a cyclone develops over the Bay of Bengal, the impact can be very different and severe due to La Nina. So, we have to see,” said DS Pai, senior scientist, India Meteorological Department (IMD), Pune.
M Mohapatra, director-general, IMD, said La Nina is good for the southwest monsoon but it does not have a favourable impact on the northeast monsoon (post-monsoon season). “We may record less rain in the post-monsoon period due to the La Nina effect.”
Northeast monsoon brings rain to the Peninsular region during October and November.
El Niño and the Southern Oscillation (ENSO) is a periodic fluctuation in sea surface temperature and the air pressure of the overlying atmosphere across the equatorial Pacific Ocean, according to the National Oceanic and Atmospheric Administration (NOAA).
ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought. El Niño has a warming influence on global temperatures, while La Niña has the opposite impact. In India, for example, El Nino is associated with drought or weak monsoon. La Nina is associated with strong monsoon and above-average rains. Last year was a weak El Nino year and June had recorded extremely arid conditions in different parts of the country and the month ended with a 33% rain deficiency.
WMO said below-average sea surface temperatures forecasted in the eastern tropical Pacific are leading to La Niña conditions. Global models and expert opinion indicate a 60% chance of La Niña development during September-November. The probability of ENSO-neutral conditions is 40% and El Niño near 0%.
The last La Niña event was in 2017-18. It was short-lived; a weak-to-moderate event that started developing in November 2017 and decayed in April 2018, according to WMO. Tropical Pacific has been in ENSO neutral condition since July and since May sea surface temperatures in the region have been slightly below average, it added.
But WMO underlined the warming influence of climate change will not be negated by La Nina. “Even if a La Niña event does develop, its cooling signal will not be enough to counterbalance the impact of human-induced climate change,” said WMO secretary-general Petteri Taalas.
“2020 remains on track to be one of the warmest years on record, with much extreme weather ranging from scorching temperatures and wildfires to devastating floods and marine heatwaves which is largely the result of greenhouse gases rather than naturally occurring climate drivers,” he said in a statement on Thursday.
WMO’s Global Seasonal Climate Update indicates that sea surface temperatures for September to November overall are expected to be above average for much of the globe and this will also influence land surface temperatures.