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Global warming alters rainfall pattern
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- Global warming has altered a key weather system and that may be whetting cyclones in the Bay of Bengal, decreasing winter rain in north India and altering global rainfall patterns, a study by a team of Indian and U.S. researchers has found.
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- Study Published in: Journal “Nature”
- Findings of the study: Madden–Julian Oscillation (MJO)
(1) A moving band of rain clouds that travels around the globe spanning 12,000–20,000 km across the tropical oceans.
(2) In its journey, it interacts with surface waters of the Indo-Pacific ocean, the largest pool of warm water in the globe, due to which the life cycle of MJO gets affected.
(3) MJO clouds on average are spending only 15 days, instead of 19, over the Indian Ocean.
(4) Over the west Pacific, it increased by five days (from an average 16 days to 23 days).
(5) It is this change in the residence time of MJO clouds that has altered the weather patterns across the globe.
(6) When the MJO appears in the Indian Ocean during the monsoon months of June-September, it can increase rains over India.
(7) This year, India was poised to receive below normal monsoon rainfall in April but ended up with excessive rain partly due to the MJO.
(8) The study doesn’t delve into the impact of the MJO during the monsoon months. However, one of the researchers said change in MJO could drift warmer surface water towards the Bay of Bengal and increase cyclones.
(9) The MJOs haven’t been as extensively studied as say the El Nino.
- This study shows that we need better observation of the Indian Ocean and improve forecasts that can warn us about a cyclone.
- Ocean temperatures
- To compute the reduction in the number of MJO days over the Indian Ocean, the scientists from the U.S. National Oceanic and Atmospheric Administration (NOAA), University of Washington & University of Tokyo, compared ocean temperatures from 1981-2018 for changes.
- Global warming has been expanding the size of the warm pool on average by 2,300 sq. km. annually from 1900-2018 and at an accelerated average rate of 4,000 sq. km. per year during 1981–2018.
- Changes in MJO behaviour have increased the rainfall over northern Australia, west Pacific, Amazon basin, southwest Africa and southeast Asia (Indonesia, Philippines and Papua New Guinea).
- At the same time these changes have brought a decline in rainfall over central Pacific, along the west and east coast of U.S. (e.g., California), north India, east Africa and the Yangtze basin in China.
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Sources
The Hindu