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Friday, Dec 13, 2019

India’s rain pattern getting affected by global climate crisis

In a report published on Wednesday, climate scientists pointed out that the Indo-Pacific warm pool, a stretch of ocean where the temperature remains above 28°C in the winter months, has doubled in size between 1981 ans 2018.

india Updated: Nov 28, 2019 03:29 IST
Jayashree Nandi and Snehal Fernandes
Jayashree Nandi and Snehal Fernandes
Hindustan Times, New Delhi/Mumbai
Scientists have for the first time linked a specific phenomenon brought on by the climate crisis to reduced winter rain in India
Scientists have for the first time linked a specific phenomenon brought on by the climate crisis to reduced winter rain in India(Satyabrata Tripathy/HT Photo)
         

Scientists have for the first time linked a specific phenomenon brought on by the climate crisis to reduced winter rain in India -- a growing patch of warm seas in the Indo-Pacific ocean region that is causing droughts in some regions across the world and extreme floods in others.

In a report published on Wednesday, climate scientists pointed out that the Indo-Pacific warm pool, a stretch of ocean where the temperature remains above 28°C in the winter months, has doubled in size between 1981 ans 2018. This, in turn, has “warped” the Madden-Julian Oscillation (MJO), a band of rain clouds that moves eastwards over the tropics and is responsible for most weather variations in the region -- including the south-west and north-east monsoons.

The study, published in the journal Nature and authored by scientists from Pune’s Indian Institute of Tropical Meteorology (IITM), United States’s National Oceanic and Atmospheric Administration, University of Washington and University of Tokyo, said that the changes to MJO have a cascading effect that triggers extreme weather events across the globe.

The MJO season begins in October and lasts till April, and the report contends its “warping” has a direct link to lower rainfall in the winter months in north India. Experts separately say the effects also spill over to the summer monsoon,which is crucial for India’s agriculture and economy.

The landmark study comes less than a week before 197 countries gather for the UN Climate Conference (COP25) in Madrid to negotiate on rules around the functioning of carbon markets, how vulnerable countries can be compensated for the loss caused by climate impact, and to decide on how findings of Intergovernmental Panel on Climate Change (IPCC’s) 2019 report on land and oceans can be taken on board.

“The MJO location-specific changes in terms of their lifespan has altered weather patterns across the globe because it changes atmospheric circulation that can enhance or suppress tropical rainfall variability, modulate or trigger extreme weather events including hurricanes, droughts, flooding, heat waves and cold surges,” said Roxy Mathew Koll, principal investigator and climate scientist, IITM.

Previous studies have established that an increase in greenhouse gas emissions due to human activities has led to the warming of the Indo-Pacific pool, the study noted.

The study looked at climate model simulations between 1981 and 2018 and found that MJO clouds now remain in Indian Ocean for four fewer days (from an average of 19 days to 15 days). In turn, they have spilled over to the west Pacific region, where they linger for five more days (from an average of 18 days to 23 days).

MJO travels 12,000-20,000km mainly over the Indo-Pacific warm pool and modulates the El Niño Southern Oscillation, tropical cyclones and the monsoons, contributing to severe weather events over Asia, Australia, Africa, Europe and the Americas.

Koll said changes in MJO can affect western disturbances that bring rain to north India and may also reduce the span of summer monsoon rains and cause extreme rainfall events in short duration.

Raghu Murtugudde, professor of atmospheric and oceanic science and earth system science at the University of Maryland, who was not involved in the study, said the report is critical for the Indian monsoon because the MJO season (October to April) dovetails the monsoon season, also known as the Monsoon Intraseasonal Oscillation or MISO season (May to September).

“The monsoon is all about MISOs or active/break periods. Since the variability and change in the monsoon are all manifest in active/break periods and our agriculture depends on active/breaks, this MJO story raises new questions about how MISOs are responding to the Indo-Pacific warm pool changes,” said Murtugudde. “Now the question is to see how MJO changes are related to the MISO changes and what it means for the future of the monsoon.”

A third scientist supported the concerns. “It’s quite possible that changes in MJO are impacting the north-east monsoon. It definitely has a big impact on our summer monsoon which is being documented. MJO is one of fundamental oscillations that impacts the intra-seasonal variability of southwest monsoon,” said SK Dash, climate scientist, IIT Delhi.

In addition to India, the impact spreads to central and east Pacific, east Africa, the Yangtze basin in China, and the east and west coasts of the United States. It is also linked to enhanced rainfall over the Maritime Continent–west pacific region, the Amazon basin in South America, south-west Africa and northern Australia.

The study links MJO changes to California droughts in 2013-2014, South-east Asia floods in 2011 and East Africa droughts in 2011, which occurred during years when the MJO phase duration was longer over the west pacific region. Extreme flooding events in Brazil, such as the 2011 Rio de Janeiro floods are also linked to longer MJO