La Nina: A Weatherman Explains How 'The Girl' Aids Monsoon Rains
Normal- to above-normal monsoons over the past few years are attributable to an irregular climate phenomenon called La Nina.
India is on course to see a fourth straight year of normal-to-above-normal monsoon, a rarity for the country which relies on the June-September rainfall to irrigate over half of its farmland.
While the distribution has been uneven, with a few states around the Gangetic plains reeling from deficient rains, overall the country has received rainfall which is higher than the long-term average so far.
The spate of normal to above-normal monsoon seasons over the past few years is attributable to an irregular climate phenomenon called La Nina, Spanish for 'The Girl'.
"La Nina favourably influences the Indian monsoon," said GP Sharma, president of meteorology and climate change, at Skymet Weather.
What's La Nina?
La Nina is observed when cold weather conditions are formed over the equatorial region of the Pacific Ocean, closer to the western coast of South America, Sharma said.
Sea surface temperatures fall and consistently remain below 0.5 degree Celsius or more of the long-term average. This strengthens the winds that blow from east to west, resulting in more rainfall over regions in South Asia, including India.
It doesn't necessarily lead to deluge and flooding all the time, Sharma said. "But it averts the possibilities of drought and mostly keeps you in a comfortable range of normal-to-above-normal rainfall."
La Nina is part of the broader weather event termed the El Nino Southern Oscillation. It is a periodic, but irregular and an unpredictable phenomenon that causes variations in the winds and sea surface temperatures. It has far-reaching consequences on global climate patterns.
La Nina's warm weather counterpart is El Nino—where sea temperatures rise above 0.5 degree Celsius—and is linked to increased probability of droughts in India.
Yet, they remain very hard to predict. "How these come up remains a mystery. Nobody can predict, nobody can visualise what are the conditions responsible for causing this phenomenon," Sharma said.
"When it occurs, we say El Nino or La Nina is there. But the reasons behind the formation are still a mystery."
What Explains 3 Years Of Above-Normal Monsoon?
Typically, La Nina and El Nino events occur once between two to seven years, Sharma said. El Nino is more commonly occuring than La Nina.
"They last about nine to 12 months. That's the normal period. They develop sometime around April, and are maximum around October-December. Then, they start to decline around early winters from January-February onwards. That's the normal cycle of this phenomenon."
However, the current phase of La Nina is an extreme rarity. La Nina conditions have persisted for a third year running now. It started around August 2020 and is expected to last beyond the year till about January 2023, Sharma said.
The 'triple dip La Nina' as the World Meteorological Organization calls it, is a first this century. "It is exceptional to have three consecutive years with a La Niña event," WMO Secretary-General Petteri Taalas said, in a media statement in August.
According to Sharma, this is likely to be the second longest La Nina event reliably recorded. The longest, which lasted for 36 months, was between 1973 to 1976.
And that's exactly what has helped India's monsoon rains over the last three years.
So, La Nina's Great, Right?
For the Indian monsoon, it is a certain boon. But it is also linked to more tropical cyclones forming over the Bay of Bengal. Just in 2020 and 2021, India was hit by five major cyclones.
Besides being unpredictable, La Nina also exacerbates droughts in parts of Africa and South America.
The WMO highlighted that abnormal weather events, such as the longest drought in four decades in the Horn of Africa, and record flood-causing rainfall in Australia, are "hallmarks" of La Nina.
"We are lucky in the Indian subcontinent to enjoy some of the good impacts of La Nina. But, African regions will have to go through misery. And when it lasts for a third year, it spells doom," Sharma said.
Is This Linked To Climate Change?
La Nina, like the El Nino, is a naturally occurring phenomenon.
However, what climate change does is it alters the frequency and duration of these events. Studies have suggested that extreme El Nino and La Nina events could double in frequency by the end of the century due to a warming world.
"Human-induced climate change is playing a bigger role in these events," Sharma said. "All these naturally occurring weather events now take place under the shadow of climate change."