Context

The La Niña weather phenomenon, which entered its third year in September 2022, is unlikely to continue through 2023 as per the experts of Columbia Climate School Research Institute for Climate and Society.

About

The La Nina Event: 

• La Niña involves the large-scale cooling of the ocean surface temperaturesin the central and eastern equatorial Pacific Ocean coupled with changes in the tropical atmospheric circulation (winds), pressure, and rainfall.
  • It usually has the opposite impact on weather and climate as El Niño.

Effects:  Rainfall patterns Atmospheric pressure Global atmospheric circulation

• La Niña is characterized by lower-than-normal air pressureover the western Pacific. These low-pressure zones contribute to increased rainfall. 
• La Niña years are associated with above-average trade winds, pushing the warmer waters towards Asia and drawing in cooler than normal water temps to the equatorial pacific. 
• Causes:La Niña is caused by a build-up of cooler-than-normal waters in the tropical Pacific, the area of the Pacific Ocean between the Tropic of Cancer and the Tropic of Capricorn.
• Unusually strong, eastward-moving trade winds and ocean currents bring this cold water to the surface, a process known as upwelling.

Triple La Niña  A triple La Niña or a ‘triple dip’ La Niña is a rare occurrence, lasting for three years in a row. It has happened only twice since 1950. On the contrary, the occurrence of two consecutive La Niña winters in the Northern Hemisphere is common.

Why the La Nina has continued for so long?

• Human induced climate change amplifies the impacts of naturally occurring events like La Niña.

Impacts on India:

• Monsoon: India may experience an extended monsoon lasting up to October due to La Niña.
• Agriculture: La Nina could have negative impacts on Indian agriculture.
• Farmers will be at risk of losing their standing Kharif crops if it rains during this period.
• The harvesting of the Kharif crops begins in September-end or early October. And any rain just before that would prove detrimental to the standing crops.

The El Nino-Southern Oscillation (ENSO) Mechanism: The combined phases of La Nina and El Nino are termed El Nino-Southern Oscillation (ENSO). The phenomenon affects rainfall patterns, global atmospheric circulation, and atmospheric pressure across the planet. In the neutral state (neither El Niño nor La Niña) trade winds blow east to west across the surface of the tropical Pacific Ocean, bringing warm moist air and warmer surface waters towards the western Pacific and keeping the central Pacific Ocean relatively cool.