Warming Indo-Pacific Ocean disrupting rainfall patterns globally: study

A new study led by Indian scientists has reported that rapid warming of the Indo-Pacific Ocean may be responsible for changing rainfall patterns in many parts of the globe, including India.

The warming pools of the Indo-Pacific Ocean are expanding and this, in turn, is altering a major weather phenomenon known as the Madden Julian Oscillation (MJO). The changes in the behaviour of MJO impacts rainfall patterns globally. The warming of Indo-Pacific Ocean is occurring due to man-made emissions.

On the one hand, these 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). On the other hand, these very changes are causing a decline in the rainfall over central Pacific, along the west and east coast of United States, North India, east Africa, and the Yangtze basin in China, according to research findings reported in international scientific journal Nature.

Specifically over north India, the impact is being seen in the form of reducing the rainfall during the winter-spring season (November to April). “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,” explained Roxy Mathew Koll of the Pune-based Indian Institute of Tropical Meteorology (IITM) who led the study.

Asked if the changes in MJO behaviour are resulting in any impact on rainfall during the summer monsoon (June to September)as well, Koll told India Science Wire: “during summer season, the warm pool waters cover the equatorial and north Indian Ocean. It is hence important to extend this study to see if there are similar changes in the summer warm pool, which may impact the summer monsoon rains over India.”

Vimal Mishra, climate scientist at IIT Gandhinagar, who was not associated with the study, commented that “the expansion of the warm pool due to anthropogenic warming has implications on climate and weather in many regions of the world. Due to this expansion, the MJO duration has gone down and this can reduce the rainfall in the Gangetic Plain.”

“It is noteworthy that previous studies have shown that decline in the rainfall in the Gangetic Plains is linked with the warming of Indian Ocean. But the new study shows that it is multi-dimensional impacts of climate warming that lead to changes in the mean and extreme rainfall. It has further indicated the need of more work on understanding of the changing complexities of the summer monsoon under the warming climate,” Mishra told India Science Wire.

Koll said “we need to enhance our ocean observational arrays to monitor these changes accurately, and update our climate models to skilfully to predict the challenges presented by a warming world.”

The extent of increase in Indo-Pacific warm pools is almost twofold. The warm pool expanded from an area of 2.2 × 107 square km during 1900–1980 to an area of 4 × 107 square during 1981–2018. The rate of expansion is 4 × 105 square km. This is critical given the fact that these pools are the largest expanse of the warmest ocean temperatures on the planet.

Though the entire Indo-Pacific has warmed, the warmest waters are over the west Pacific, creating a temperature contrast that drives moisture from the Indian Ocean to the west Pacific Maritime Continent, enhancing the cloud formation there. 

MJO is basically a band of rain clouds moving eastward, traveling a stretch of 12,000 to 20,000 kms over the tropical oceans. The warming ocean pool has altered its life cycle. The residence time of MJO clouds has shortened over the Indian Ocean by 4 days (from an average of 19 days to 15 days), while it has increased over the west Pacific by 5 days. It is this change that is altered the weather patterns across the globe.

“There are coordinated international efforts underway to extend the range of accurate weather forecasts out to lead times of two to four weeks and the MJO is one of the most important keys to the success of this enterprise,” pointed out Michael McPhaden, a member of the study team and senior scientist at the U.S. National Oceanic and Atmospheric Administration (NOAA).

The study team also included Panini Dasgupta (IITM), Chidong Zhang (NOAA), Deahyun Kim (University of Washington) and Tamaki Suematsu (University of Tokyo). (India Science Wire)

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