India is expected to receive normal rainfall during the southwest monsoon season this year, according to the Indian Meteorological Department (IMD). However, experts claim that climate change and other factors will significantly impact India's monsoon. These factors include the Indian Ocean Dipole (IOD) and an El Niño year following a triple-dip La Niña.
Experts say that several factors may result in “below normal” monsoon rainfall in 2023.
What is El Niño?
When conditions in the Pacific Ocean are normal, trade winds blow west along the equator. Trade winds are steady winds which flow towards the equator from the north-east in the Northern Hemisphere or the south-east in the Southern Hemisphere, especially at sea. These winds take warm water towards Asia.
Cold water rises from the depths to replace the warm water. This process is called upwelling. However, there are two conditions which break these normal conditions — El Niño and La Niña. El Niño is also known as the El Niño-Southern Oscillation (ENSO) cycle and can impact weather patterns globally.
Both El Niño and La Niña typically last nine to 12 months, and can occur every two to seven years, on average.
El Niño is the phenomenon in which trade winds weaken, as a result of which warm water is pushed back east, toward the west coast of the Americas, where the Pacific Ocean is present.
Since warm water has been pushed back east due to El Niño, the monsoon in India is likely to be affected.
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What is La Niña?
The La Niña effect is believed to be one of the reasons behind the changes in seasonal weather patterns of India. The periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific is referred to as the La Niña effect. While the La Niña effect occurs every three to five years, occasionally, it can take place over successive years.
La Niña means “Little Girl” in Spanish, and is sometimes also called El Viejo, or simply a “cold event”.
According to the National Oceanic and Atmospheric Administration (NOAA), La Niña is the opposite of El Niño, the event in which warm water is pushed towards the west coast of the Americas.
Meanwhile, during La Niña events, trade winds, which are winds blowing steadily towards the equator from the north-east in the Northern Hemisphere or the south-east in the Southern Hemisphere, become stronger than usual. As a result, warm water is pushed toward Asia.
Off the west coast of the Americas, cold, nutrient-rich water is brought to the surface.
The La Niña event lasted till February 2023. According to the World Meteorological Organization (WMO), this was the first “triple-dip” La Niña of the 21st century, which means that the La Niña effect had been occurring for three consecutive years.
The triple-dip La Niña affected temperature and precipitation patterns in different parts of the world. While La Niña is associated with cooler than normal winters in the Northern Hemisphere, it increased global temperatures in 2022 because the effect has been taking place against a background of human-induced climate change. This made India’s weather more extreme, and affected seasonal weather patterns.
According to the WMO, more intense and longer monsoon rainfall in southeast Asia is associated with La Niña.
Widespread warmer than average sea surface temperatures in regions other than the equatorial central and East Pacific are believed to be responsible for the above-normal temperatures along the Arctic coast of Asia.
Why an El Niño year following a La Niña year is the worst-case scenario for monsoon deficits
Experts say that an El Niño year following a La Niña year is the worst-case scenario for monsoon deficits.
The reason behind this is that La Niña conditions usually bring above-average rainfall to India, while El Niño brings drier-than-normal conditions. As a result, the combination of the two events has a significantly negative impact on monsoon rainfall.
“An El Niño year following a La Niña year is the worst-case scenario for monsoon deficits because La Niña conditions usually bring above-average rainfall to India, while El Niño brings drier-than-normal conditions. During La Niña, the Pacific Ocean becomes cooler than normal, strengthening the easterly winds and increasing rainfall over the Indian subcontinent. However, during El Niño, the Pacific Ocean becomes warmer than normal, weakening the easterly winds and decreasing rainfall over the Indian subcontinent,” Dr Anjal Prakash, Research Director, Bharti Institute of Public Policy, Indian School of Business and IPCC Author, told ABP Live.
Dr Prakash explained that when the two events occur consecutively, there may be a large rainfall deficit.
“When these two events occur consecutively, the monsoon season can be severely impacted, leading to a large rainfall deficit. The excess rainfall during the La Niña year can result in flooding, soil erosion, and crop damage. In contrast, the dry conditions during the following El Niño year can lead to drought-like conditions, water scarcity, and crop failure,” Dr Prakash said.
He concluded that the combination of the two events can significantly negatively impact agriculture, water supply, and the economy, making it the worst-case scenario for monsoon deficits.