As the monsoon hit the Kerala coast, the US National Oceanic and Atmospheric Administration (NOAA) declared that the equatorial Pacific Ocean was firmly in the El Nino phase.
Over India, the El Nino results in suppressed rainfall during the monsoon season.
El Nino, which in Spanish means little boy, refers to an abnormal warming of the sea surface waters in the equatorial Pacific Ocean that influences weather events globally.
“Depending on its strength, El Nino can cause a range of impacts such as increasing the risk of heavy rainfall and droughts in certain locations around the world,” Michelle L’Heureux, climate scientist at the Climate Prediction Center, NOAA, said in a press statement.
The current El Nino event is the fifth since 2000. The sea surface waters in the Pacific Ocean alternate between a warm and cold phase every two to seven years, with a neutral phase thrown in between. This fluctuating system is called El Nino Southern Oscillation, or ENSO.
The cold phase, or La Nina, usually has opposite impacts compared to El Nino.
At the start of this year, El Nino was predicted to emerge in August. But revised predictions suggested that it would form during the May-July period. However, the sudden gain in strength of the El Nino has surpassed expectations.
Sea surface temperatures along the equatorial Pacific Ocean, especially along the various Nino regions, were showing signs of rapid warming. The Nino 3.4 index value – the vital indicator confirming an event of El Nino – jumped from minus 0.2 degrees Celsius to 0.8 degrees Celsius between March and June this year.
The threshold value for this index for El Nino to be declared is 0.5 degrees Celsius.
Meteorologists had noted that such accelerated rates of warming, following three years of La Nina that ended in February this year, was unusual.
The India experience
In India, there have been 18 drought years over 100 years. Of these, 13 years were associated with El Nino. Between 1900 and 1950, there were 7 El Nino years but in 1951-2021, there were 15 El Nino years. Of these, nine summer monsoon seasons recorded deficient rain.
During ENSO neutral conditions, the trade winds blow west along the equator and take the warm water from South America towards Asia. Whereas, during an event of El Nino, these trade winds weaken and instead reach the coasts of western America. During such years, there prevails warmer-than-average sea surface temperatures along the equatorial Pacific Ocean.
In the Indian context, over the last hundred years there have been 18 drought years. Of these, 13 years were associated with El Nino. Between 1900 and 1950, there were 7 El Nino years but in the 1951 to 2021 period, there were 15 El Nino years (2015, 2009, 2004, 2002, 1997, 1991, 1987, 1982, 1972, 1969, 1965, 1963, 1957, 1953 and 1951). Of these, nine summer monsoon seasons over the country recorded deficient rain by more than 90 per cent of the Long Period Average.
“Climate change can exacerbate or mitigate certain impacts related to El Nino. It could lead to new records for temperatures, particularly in areas that already experience above-average temperatures,” L’Heureux said.
* Anjali Marar works at the Raman Research Institute, Bengaluru.
