The Indian monsoon - long known for its steady and gentle falls - is succumbing to "human-induced" changes to become more abrupt, according to a new multinational study led by a climate scientist from the state-run Indian Institute of Tropical Meteorology (IITM) in Pune.
Two studies, steered by monsoon investigator R Krishnan of the IITM and his international partners, have presented the first evidence of how pollution and change in patterns of land use are impacting India's main rain-bearing system. As opposed to historically softer and evenly spread rains, the monsoon now features more localised, extreme and sharper falls, with abrupt "start-stop" cycles and "significant rise" in monsoon breaks or long pauses during a season.
Some of these impacts may have been brought on by sweeping economic progress in neighbouring China, with its copious aerosol emissions in the past 50 years, evidence suggests. "We found that the monsoon is now more characterised by intense precipitation at the expense of moderate events," Krishnan told HT.
His team concluded that pollutants such as black carbon and aerosols as well as changing land-use patterns like deforestation have weakened the monsoon. "China's development could be affecting the monsoon. Its aerosol use is now well recognised," said Krishnan.
Even more worrisome are findings that the monsoon has been declining in the Western Ghats, Jharkhand and Chhattisgarh by 6-7%.
Krishnan and his team also stumbled upon a vicious cycle. A weakening monsoon circulation has quickened the warming of the equatorial Indian Ocean which, in turn, has contributed to a weakening of the monsoon. "Our studies show the Indian Ocean has significantly warmed in 50 years by about 0.6 degrees," Krishnan said.
"Although the frequency of extreme rainfall events have increased in certain parts of the country, it is the decreasing trend in moderate-to-heavy monsoon rainfall events that poses an enormous long-term concern for one of the most densely populated regions of the world that heavily depends on the monsoonal rains," the authors wrote in Climate Dynamics.
The new findings portend problems India isn't currently prepared to address. Two-thirds of Indians rely on rain-fed farm income. The monsoon replenishes 81 nationally important water reservoirs critical for drinking, power and irrigation. Such changes could prompt a shift in farm belts, hamper food security and affect livelihood of millions.
During the studies, Krishnan, along with M Sugi of the Meteorological Research Institute in Japan, applied a Japanese model to track the monsoon's changes. While one of the studies is under peer review (a necessary academic step), the other one has been published in the prestigious Climate Dynamics journal.