The Delhi government and IIT Kanpur have begun cloud-seeding to try and induce rain and curb toxic air pollution, a move some weather scientists caution appears driven more by demand than by evidence.
The artificial rain is meant to wash out pollutants that have pushed air quality across the national capital region into the “very-poor” category over the past week. But experts, including some who have evaluated cloud seeding, have questioned the viability of this approach.
A Cessna aircraft took off from Kanpur on Tuesday and released flares containing sodium iodide and sodium chloride particles over several areas across Delhi, the first of a series of “cloud-seeding trials” planned over the next few days.
Till late into the night, the weather department had not recorded any traces of rain in the city.
“This is a huge step taken by the government to mitigate pollution. If the trials are successful, we will prepare a long-term plan,” Delhi’s environment minister Manjinder Singh Sirsa was quoted as saying in a PTI report.
A nationwide air quality monitoring network recorded Delhi’s average levels of tiny particulate matter size 10 microns (PM 2.5) to be 136 micrograms per cubic metre at 7pm on Tuesday — about nine times the 15 micrograms per cubic metre limit recommended by the World Health Organisation.
Earlier this year, the Delhi government had approved the ₹3.2-crore cloud-seeding trials and last month signed a pact with IIT Kanpur for trials around northwest Delhi, according to PTI.
A test flight over north Delhi last week failed to produce rain because atmospheric moisture was below 20 per cent, short of the 50 per cent typically required for cloud-seeding, PTI reported.
Scientists familiar with cloud-seeding research say the failed test raises questions about whether the trials are considering key quantitative criteria such as cloud moisture, temperature and updraft wind.
Some of the criteria had emerged from the world’s largest randomised cloud-seeding trial conducted by the Indian Institute of Tropical Meteorology (IITM), Pune, during 2018-2019, measuring rainfall from 151 seeded and 125 non-seeded clouds.
“We documented on average about 18 per cent more rainfall from seeded than from non-seeded clouds,” Thara Prabhakaran, the IITM scientist who had led the trial, told The Telegraph.
Authorities in China, South Korea and Pakistan have also tried to address air pollution through cloud-seeding but experts say the evidence for its effectiveness remains limited, inconsistent and largely short-term.
“This is not a viable solution to air pollution,” said Madhavan Rajeevan, a senior atmospheric physicist and former secretary of the Union earth sciences department. “Even if there is some induced rain, it’s unclear how long its effect will last in the continued presence of the pollution sources — the real solution lies in finding ways to reduce or curb the pollution.”
An IIT Kanpur faculty member had told PTI in December 2023 that the institute had “developed a novel seeding solution of salts which has been tried for cloud-seeding for artificial rain”.
A query sent by this newspaper on Tuesday to the faculty member seeking responses to scientists’ concerns went unanswered. The faculty member also did not reply to a question on whether Tuesday’s trial produced any rain. Studies suggest that artificial rain, when it occurs, typically appears within 30 minutes to 3 hours after seeding.
But two Indian scientists familiar with cloud-seeding research said they were not aware of any research study in the country that had evaluated in a rigorous, quantified manner whether and by how much cloud-seeding cou;d lower air pollution and for how long.
The government’s weather and air quality agency forecast says Delhi’s air will stay “very poor” until October 31 and fluctuate between poor and very poor over the following six days.