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IITM Researchers Say Global Warming Behind Monsoon Decline Over a Century

As India eagerly awaits for a better monsoon every year, the gradual decline in the rain-fed agricultural states is alarmingly visible, making meteorologists to link it to the possible global warming.

Pune-based Indian Institute of Tropical Meteorology (IITM) has noted in its latest research paper that the rapid warming in the Indian Ocean has been weakening the monsoon consistently with 10% to 20% deficient rains every year in the mean rainfall over the last 112 years in Central India, especially the states of Uttar Pradesh, Jharkhand, Madhya Pradesh, Uttarakhand and Chhattisgarh.

The study, published in the journal ‘Nature Communications’, used multiple observed datasets to show that a significant weakening trend in summer rainfall during 1901–2012 over the central-east and northern regions of India, along the Ganges-Brahmaputra-Meghna basins and the Himalayan foothills, where agriculture is still largely rain-fed.

“The land-sea thermal gradient over South Asia has been decreasing, due to rapid warming in the Indian Ocean and a relatively subdued warming over the subcontinent,” IITM scientist Roxy Mathew Koll said in the article.

The evidence is compelling that the enhanced Indian Ocean warming potentially weakens the land-sea thermal contrast, dampens the summer monsoon Hadley circulation, and thereby reduces the rainfall over parts of South Asia, the said in their research paper.

One of the major monsoon drivers is the land-sea temperature difference in summerthat has reduced in the past decades. “This reduction in land-sea temperature is primarily contributed by a strong warming in the Indian Ocean. The surface warming in the Indian Ocean, especially that in the western regions, has reached up to values of 1.2°C during the past century, much greater than the warming trends in the other tropical oceans,” said Koll.

The study was conducted as part of an Indo-French collaboration under the National Monsoon Mission setup by the Ministry of Earth Sciences.

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