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Did you know Indian and West African monsoons are linked....

Sonali

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Did you know Indian and West African monsoons are linked....
« on: February 01, 2019, 09:52:56 PM »

https://www.downtoearth.org.in/news/science-technology/did-you-know-indian-and-west-african-monsoons-are-linked--63043

Did you know Indian and West African monsoons are linked?
A report by an IISc scientist says that El Nino oscillates between both regions and affects the intensity of their rainfall



We all knew that monsoon in both India and West Africa is intimately linked to the regions’ agriculture economies, which is mostly either rain fed or irrigated by rivers that too depend on rains to maintain flow. But now scientists have found that rains in these regions might also be linked to each other through the El Nino Southern Oscillation (ENSO) phenomenon which affects both of them. 

A recent research paper published in the journal Climate Dynamics says ENSO’s relationship with Indian Summer Monsoon (ISM) has shifted towards the West African Summer Monsoon (WASM). For example, between 1911 and 1930 while the influence of ENSO on ISM was weak, the influence of ENSO on WASM was strong. It also says that this shift is part of a multi decadal cycle, which weakens ENSO’s relationship with ISM while strengthening its relationship with the WASM and vice versa.

And, between 1931 and 1980 these influences reversed in character. Then they flipped again between 1981 and 2015. The reason behind this see-saw relationship is a shift in one half of ENSO’s temperature gradient (cooling part) from the north west of the Indian Monsoon region to the northern part of West Africa.

But there is a catch. Current models do not agree and correctly predict that if this is going to shift again or how much time it will take to do so in a world reeling under climate change. The physics of Earth’s climate, especially regarding a large-scale phenomenon like El Nino, is too complicated to be simulated by computational models even ones that are currently using artificial intelligence. But, this might improve with better dynamic climate models which are closer to how clouds and turbulence actually behave in our atmosphere.

The warm phase of the ENSO or the El Nino refers to the unusual warming of the central and east-central equatorial Pacific Ocean which affects global weather including India and West Africa. The other half of this oscillation is formed by the cooling of the north western Indian monsoon region or the northern part of West Africa.

During El Nino, the warmer waters of the Pacific Ocean cause the winds in various regions, like the trade winds that come towards India, to reverse. This change of wind direction can lead to warmer winters and summers and a decrease in rainfall during the monsoon. Sometimes it also leads to drought.

In the cooling phase of the ENSO, known as the La Nina, the exact opposite of these events happen which might lead to increased rainfall inducing floods, flash floods and landslides.

In fact, the paper states, “During 1901-2015, the ISM recorded 22 droughts, of which nine were associated with El Niño and of the 18 floods recorded in that period, nine were associated with La Niña. On the other hand, for WASM, out of 21 droughts, nine were associated with El Niño, while of the 22 floods, seven were caused by La Niña, implying that 45 per cent of the ISM and 39 per cent of the WASM rainfall extremes are associated with ENSO.”....
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Thanks & Regards

Sonali Pattanayak
Research Associate
Divecha Center for Climate Change
IISc,Bangalore-12