Emergence of La Niña delayed

Context

  • Multiple global weather models have forecasted a delayed emergence of La Niña the periodic cooling of ocean surface temperature in the equatorial Pacific Ocean.
    • While earlier they expected La Niña’s onset around July, the latest data show that it will develop during September or later.
    • The climate pattern, known to favour rainfall during the monsoon season in India, is one of the three phases of the El Nino Southern Oscillation (ENSO).
La Niña
Credit: NBC News

Will La Nina impact the Indian monsoon?

  • This year, the India Meteorological Department (IMD) has forecast an ‘above’ normal rainfall during June – September.
  • The seasonal rainfall is expected to be 106% of the Long Period Average of 880 mm (1971 – 2020 records).
  • July rainfall looks promising as the country is expected to continue receiving widespread rainfall in the next ten days.
  • Rainfall during July and August accounts for nearly 70% of the country’s seasonal rainfall.
  • Even if La Niña conditions emerge by September, meteorologists do not see any cause for alarm.
  • The delayed development of La Niña may not have a serious impact on the monsoon’s performance over India.
  • Even though La Niña conditions favour good monsoon rainfall, it is not essential.
  • In recent years, the southwest monsoon has overstayed its forecast period with its complete retreat from the country extending well into mid-October or later.
  • If La Niña conditions emerge by September climatologically the last month of the monsoon there is a strong possibility of above normal rainfall during the final monsoon month.
  • The rainfall during September amounts to 15% of the seasonal rainfall.

What is ENSO?

  • The El Nino Southern Oscillation (ENSO) is a climate phenomenon characterised by changes in sea temperatures along the central and eastern tropical Pacific Ocean, coupled with fluctuations in the overlying atmosphere.
  • It can alter and interfere with the global atmospheric circulation, which, in turn, influences the weather worldwide. ENSO has three phases – warm (El Niño), cool (La Niña), and neutral.
  • It occurs in irregular cycles of 2 to 7 years.
  • In the neutral phase, the eastern side of the Pacific Ocean (near the northwestern coast of South America) is cooler than the western side (near the Philippines and Indonesia).
  • This is due to the prevailing wind systems that move from east to west, sweeping the warmer surface waters towards the Indonesian coast.
  • The relatively cooler waters from below come up to replace the displaced water.
  • These wind systems weaken in the El Niño phase leading to lesser displacement of warmer waters.
  • As a result, the eastern side of the Pacific becomes warmer than usual. In the La Niña phase, the opposite happens.
  • The latest El Niño event prevailed between June 2023 and May 2024, whereas La Niña conditions lasted three consecutive years between 2020 and 2023.
  • Initial projections by global weather models earlier this year had forecast the onset of La Niña conditions around July. However, ENSO-neutral conditions continue to persist with the temperature along the Nino 3.4 – the main region along the equatorial Pacific Ocean suggesting the ENSO conditions – remaining on the warmer side.

Source: IE

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