In continuation of our blog on the Indian Ocean Dipole(IOD), this week we discuss the reasons behind the irregularity in the monsoon seasons.

This week, our blog is mediated by a special guest Balaji aka “Telangana Weatherman”.

To start the conversation, our weatherman talks about El Nino and La Nina.

An El Niño is declared when the average sea surface temperatures in the east-central tropical Pacific (in the Nino 3.4 region), stay more than 0.5 degrees Celsius above the long-term average for five consecutive months. And the opposite is La Nina, where the average sea surface temperature is cooler. Sea surface height and ocean colour, surface winds, and cloudlines/precipitation are also measured.

Our Telangana Weatherman says “The irregularity we experience in the monsoon season is down to events like El Nino, La Nina and IOD.” Speaking specifically concerning the Telangana region in India, he says “La Nina and negative IOD events have influenced higher rains than usual in the recent past. As we’ve seen, we’ve got floods in Hyderabad in 2019-2022. Even 2022 had many flood events. All these factors supported the excess rainfall in Telangana for the last 4 years.”

“And not just Telangana, the core monsoon zone usually include states/regions like Chattisgarh, Madhya Pradesh, Odisha, Maharashtra, West Bengal, Uttar Pradesh and Bihar, and depending on the rainfall in this core monsoon region the rainfall in India is told to be either in excess or drought. As we’ve seen in North-East India, La Nina usually results in lower rainfall than usual, opposite to that of the Southern Peninsula. It’s vice versa when El Nino event happens.”

Adding to that, our weatherman says, “El Nino and La Nina usually follow a periodic pattern — not exactly in an ideal way, but it could be some months with El Nino, some months with La Nina and some months could be neutral too. There could be El Nino happening in the coming future where there could be a deficit rainfall as we’ve seen during the 2013–18 period.”

Our Telangana Weatherman also says, “El Nino and La Nina affect weather not just in India but also globally. That’s why we call them Teleconnection with the weather. El Nino and La Nina not just affect rains but also affect the way we experience summers and winters too.”

How is Climate change affecting El Nino and La Nina?

“Though we see global temperatures rising, it is usually reported in terms of average temperature. So, it is tough to correlate such averages to specific phenomena like El Nino and La Nina. The heatwave events seen in the recent past in Europe are a consequence of Global warming but El Nino is just a part, not the complete globe” says Telangana Weatherman.

“Extreme El Niño and La Niña events may increase in frequency from about every 20 years to one every 10 years by the end of the 21st century under aggressive greenhouse gas emission scenarios,” McPhaden (US NOAA- United States National Oceanic and Atmospheric Administration) said. “The strongest events may also become even stronger than they are today.”

In a warming climate, rainfall extremes are projected to shift eastward along the equator in the Pacific Ocean during El Niño events and westward during extreme La Niña events. Less clear is the potential evolution of rainfall patterns in the mid-latitudes, but extremes may be more pronounced if strong El Niños and La Niñas increase in frequency and amplitude, he said.

Some ENSO impacts are already being amplified, such as the extensive coral bleaching and increases in tropical Pacific storm activity observed during the 2015–16 El Niño.

Thanks to our Telangana Weatherman, we can now understand the weather events we experience in a better way.