Context

Australia’s Bureau of Meteorology (BOM) predicted that a third consecutive event of La Niña could be underway.

About

What is La Niña?

El Nino-Southern Oscillation (ENSO) ENSO refers to the El Niño/Southern Oscillation, the interaction between the atmosphere and ocean in the tropical Pacific. ENSO is a series of linked weather and ocean-related phenomena. El Niño is the warm phase of ENSO.

• La Niña involves the large-scale cooling of the ocean surface temperatures in 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.
• La Niña is characterized by lower-than-normal air pressure over 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 watersin 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.
• Effects: La Niña affect
  • patterns of rainfall
  • atmospheric pressure
  • global atmospheric circulation

What does a triple La Niña mean?

• 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.

Impact on India

• Monsoon: India may experience an extended monsoon lasting up to October due to La Niña.
  • The India Meteorological India (IMD) has predicted that monsoon withdrawal may begin in the first week of September, but it is likely that some parts of India may continue to witness heavy rains.

Impact of El Nino and La Nina El Nino is associated with drought or weak monsoons. La Nina is associated with strong monsoons and above average rains and colder winters.

• 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.