THE IMPACT OF EL NINO ON NORTHEAST MONSOON AND SOUTH TAMIL NADU DELUGE

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TAG: GS 1: GEOGRAPHY

THE CONTEXT: The recent deluge in south Tamil Nadu, particularly in areas like Thoothukudi and Tirunelveli, has been attributed to an active Northeast monsoon (NEM) intensified by the El Nino phenomenon.

EXPLANATION:

• El Nino, characterized by warmer-than-normal temperatures in the central and eastern Pacific Ocean, is a phase of the El Nino Southern Oscillation Phenomenon (ENSO).
• This phase tends to augment rainfall extremes, specifically during the Northeast monsoon period.

Impact of El Nino on Rainfall Extremes

• Studies indicate that extreme rainfall occurrences during the Northeast monsoon in regions of southern Tamil Nadu are notably more frequent than during the Southwest monsoon season.
• The recent heavy rainfall is a reflection of this pattern, with five districts experiencing significant downpours, surpassing normal rainfall levels by staggering percentages.
• Tirunelveli received 363.6 mm of rainfall, an astonishing 5,094% higher than the usual amount.
• Thoothukudi encountered 343.6 mm of rain, exceeding the normal by 7,059%.
• Other affected districts include Tenkasi, Virudhunagar, and Kanyakumari, each experiencing substantial rainfall exceeding the expected averages.

Meteorological Factors Contributing to Extreme Rainfall

• Experts emphasize the contribution of the El Nino phenomenon in intensifying the Northeast monsoon, thereby creating conducive conditions for extreme rainfall events.
• Factors contributing to the deluge include:
  • Cyclonic Circulations:
    • These atmospheric whirls in upper layers induce low-pressure areas, leading to rainfall.
    • The presence of cyclonic circulations, particularly near Kanyakumari, facilitated strong upper-level divergence.
    • This resulted in significant low-level convergence of moisture-laden winds towards south Tamil Nadu.
  • Upper-Level Divergence and Low-Level Convergence:
    • The spreading out of air in the upper atmosphere causes air below to rise, leading to low-level convergence.
    • This process brings moisture-laden winds, fostering extreme rainfall events.
  • Influence of Cyclonic Systems:
    • After the impact of Cyclone Michaung, a diffuse cyclonic system near the south Tamil Nadu coast further intensified northeast winds, creating wind and wave convergence over the region, especially around the gap between Sri Lanka and Tamil Nadu (Palk Bay & Gulf of Mannar).

Previous Observations and Weather Patterns

• Historically, research suggests that extreme rainfall during the Northeast monsoon (December-February) is more prevalent in the southern regions of Tamil Nadu and Sri Lanka compared to the Southwest monsoon (June-September).
• Studies analyzing 30 different weather patterns have identified specific climate variability, with certain patterns significantly associated with extreme rainfall occurrences in autumn and winter around Sri Lanka and south Tamil Nadu.

EL-NINO:

• El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which is characterized by unusually cold ocean temperatures in the Equatorial Pacific.
• El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe.
• Among these consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.
• Observations of conditions in the tropical Pacific are considered essential for the prediction of short term (a few months to 1 year) climate variations.

Implications and Conclusion

• The current deluge over Thoothukudi and Tirunelveli aligns with one of these identified patterns.
• The active pattern during the NEM season strengthens the monsoon, potentially enhancing rainfall over coastal Tamil Nadu and Sri Lanka.
• In essence, the convergence of various meteorological factors, including El Nino’s influence on the Northeast monsoon, cyclonic circulations, upper-level divergence, and low-level convergence, has contributed to the recent extreme rainfall events in south Tamil Nadu.
• Understanding these complex interactions is crucial for predicting and mitigating the impacts of such extreme weather occurrences in the future.

SOURCE: https://www.downtoearth.org.in/news/climate-change/el-nino-fuelled-northeast-monsoon-caused-the-deluge-in-south-tamil-nadu-experts-93469