The World Meteorological Organization has said that La Nina may occur in the coming three months, but there is only a 55 percent chance of it happening.
Key Points:
La Niña, a phase of the El Niño Southern Oscillation (ENSO), occurs when the region of the Pacific Ocean between Indonesia and South America is cooler than usual.
Its counterpart, El Niño, represents a warming of the same region.
These two phases significantly influence global atmospheric circulation and weather patterns.
During La Niña years, India receives normal or above-normal rainfall during the monsoon season.
Yet the same phenomenon causes droughts in Africa and intensifies hurricanes over the Atlantic Ocean.
Conversely, the El Niño brings extreme summers and droughts in India while increasing rainfall in the southern United States.
While the La Niña was expected to emerge by July this year, it is yet to.
The India Meteorological Department now expects a La Niña to set in by late 2024 or early 2025, plus a milder winter due to this delay.
This decade began with three consecutive La Niña events (2020-2022), a rare occurrence known as Triple Dip La Niña, followed by an El Niño in 2023.
Climate change may increase the frequency and intensity of both La Niña and El Niño events, as rising sea and land temperatures disrupt the Pacific’s balance.
This could also amplify extreme La Niña events, which generally lead to harsh winters in India.
La Nina
The term La Nina refers to the periodic changes in the sea surface temperature of the Pacific Ocean, which affects the weather around the world.
La Nina occurs when the air pressure at the surface in the equatorial Pacific Ocean region is higher than normal.
The most popular reason for its origin is the trade winds blowing at a very fast speed from the east.
Effect of La Nina
Decline in temperature - Due to La Nina, the sea surface temperature decreases drastically, due to which the temperature around the world becomes much lower than the average.
La Nina usually causes cold weather in the north-west and hot weather in the south-east. India experiences extreme cold during this period.
Change in the direction of cyclones - La Nina can change the direction of tropical cyclones with its speed.
Effect on rainfall- It can lead to excessive rainfall in Indonesia and surrounding areas and floods in Australia. Ecuador and Peru become drought prone.
Effect on Indian Monsoon
El Nino summers tend to be relatively harsh, as was the case in April this year, when India experienced intense, record-breaking heat waves.
If La Nina arrives and persists until the summer of 2025, it could bring relief from the high heat.
Additionally, El Nino often disrupts the monsoon.
India has historically received below-average rainfall during at least half of the El Nino years since 1871.
Data also indicate an evolving pattern after 1980.
For example, both north and south India have received less rainfall during more intense El Nino events, while central India has been much less affected.
On the other hand, La Nina promotes stronger monsoons, as evidenced by “normal” or “above normal” rainfall in the La Nina years of 2020, 2021, and 2022.
The El Niño year of 2023 saw “below normal” rainfall.
Thus if La Niña forms now or early next year and continues till the monsoon season,
It will mean less intense heat and more rain for India.
This year cities in south India like Bengaluru and Hyderabad are experiencing colder-than-normal winters, while north India is experiencing a delayed winter with above-normal temperatures.
Some reports have linked the southern cold to La Niña, but current ONI values indicate the opposite.
If La Niña had already developed, north India would have likely experienced colder-than-normal winters.
An analysis of 35 years of meteorological data by researchers at the New Delhi-based Council on Energy Environment and Water showed that La Nina winters have colder nights but warmer daytime temperatures than El Nino winters.
The average wind speed is higher throughout the day during La Nina winters.
Role of La Nina in cyclone formation
Intense hurricanes and cyclones develop in the Atlantic Ocean and the Bay of Bengal during the La Nina period.
Due to many supporting factors including high relative humidity and low relative air flow over the Bay of Bengal, there is a possibility of severe cyclones in the North Indian Ocean including the Arabian Sea and the Indian Ocean.
The months from October to December after the monsoon in the North Indian Ocean are suitable for the development of cyclones. Also, November is the peak time for cyclonic activities.
Q. Who has predicted that La Nina will occur from January to March?