How does La Niña affect India’s climate?

Why in the NEWS?

• 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.