Context: 

As per the latest ENSO update from the National Oceanic and Atmospheric Administration (NOAA) of the United States La Nina conditions is predicted by the end of 2024.

El Niño & La Niña (El Niño-Southern Oscillation): By NOAA

• The latest official probabilistic forecast issued by NOAA indicates a greater than 70 per cent chance of a La Nina event during September-November 2024 with the current El Nino phenomenon in the equatorial Pacific Ocean ending by April.
• The current forecasts indicate that La Nina can arrive during the second half of the southwest monsoon season. 

El Niño-Southern Oscillation (ENSO)

• It is a recurring climate pattern which involves changes in the temperature of waters in the central and eastern tropical Pacific Ocean every three to seven years.  
• The surface waters across a large swath of the tropical Pacific Ocean warm or cool by anywhere from 1°C to 3°C, compared to normal
• Impact: The ENSO cycle directly affects rainfall distribution in the tropics and have a strong influence on weather systems across the United States, India , Australia and other parts of the world.
• Phases: It has 3 phase with  El Niño and La Niña as the extremes and in between these two is a third phase called ENSO-neutral.
  • El Niño: It is warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean along the Peruvian Coast replacing the cold Humboldt current.
    • Impact: Rainfall decreases over Indonesia and the broader South Asia while it increases over the central and eastern tropical Pacific Ocean.
    • The low-level surface winds or the Easterlies weaken or  in some cases, changes their direction and start blowing in the other direction (from west to east). 
  • La Niña: La Nina means The Little Girl in Spanish. It is cooling of the ocean surface, or below-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean along the Peruvian Coast strengthening the cold Humboldt current.
    • Impact: In a reverse from El-Nino, Indonesia and South Asia receives higher rainfall while it  decreases over the central and eastern tropical Pacific Ocean.  
    • The normal easterly winds along the equator become even stronger. 

Impact of La Nina on India 

• The latter part of the southwest monsoon season  may witness more than average rainfall for most of India.
• South west monsoon may extend  into October like in the past few years. 
• All India Mean Rainfall: It is speculated to remain in positive but states like Uttar Pradesh, Jharkhand and Bihar may again face a deficit.

• La Nina Event of 2021-2023

• • It had caused above normal and extended monsoon seasons.
  • Example: Monsoon season of 2022 ended up with an all India excess of six per cent and rains extending into October. 
  • The period also saw many extreme rainfall events and consequent floods, flash floods and landslides across many states of India, especially in the later part of the seasons. 

News Source: DTE