CHENNAI: Why is the Northeast monsoon, which is the lifeline for Tamil Nadu, becoming erratic? Are we witnessing an increase in frequency of tropical cyclones, extended dry periods, and extreme rainfall events? A new study suggests that the Indo-Pacific Ocean is warming rapidly, and there is a ‘near tw0-fold’ expansion of warm pool covering most parts of Bay of Bengal, which is affecting climatic patterns.
The study, led by Roxy Mathew Koll of the Indian Institute of Tropical Meteorology, and published in the journal Nature, reports a two-fold expansion of the Indo-Pacific warm pool -- the largest expanse of the warmest ocean temperatures on Earth. The study has found that the expansion of this warm pool has altered the Madden Julian Oscillation (MJO) -- a major fluctuation in tropical weather.
The increase in carbon emissions has been causing rapid warming and expansion of this warm pool in the recent decades. “The warm pool has expanded to become double its size, from 2.2 × 107 km2 during 1900-1980 to 4 × 107 km2 during 1981-2018,” says the study. The rate of expansion is concerning -- covering an area equal to the size of Japan every year.
Intensified cyclones
“Just before the onset of the Northeast monsoon, in October, the entire Bay of Bengal becomes part of this giant warm pool, aiding rapid intensification of cyclones,” said the study author Roxy Mathew Koll, citing the examples of cyclones Ockhi and Fani. Though the study does not talk about Northeast monsoon in specific, Koll said the study period corresponds with the monsoon activity.
“There are coordinated international efforts underway to improve the accuracy of weather forecasting. Climate model simulations indicate that continued warming of the Indo-Pacific Ocean is highly likely, which may further intensify these changes in global rainfall patterns in the future,” says Michael McPhaden from US National Oceanic and Atmospheric Administration, who was also part of the study.
Simply put, India is likely to witness more such cyclones in future.
“We need to enhance our ocean observational arrays to monitor these changes accurately and update our climate models to skilfully predict the challenges presented by a warming world,” added Koll. Other co-authors of the study are Panini Dasgupta (IITM), Deahyun Kim (University of Washington) and Tamaki Suematsu (University of Tokyo).