Authorities in Delhi tried to tackle the capital’s worsening air pollution on Tuesday by conducting a cloud seeding experiment—a method of modifying clouds to produce rain—but the trial was largely unsuccessful.
Cloud seeding involves releasing tiny particles, usually silver iodide, into clouds to trigger rainfall. While the technique is applied globally, experts question its long-term effectiveness in controlling air pollution.
A team from the Indian Institute of Technology (IIT) Kanpur, in collaboration with the Delhi government, carried out the experiment across several city neighbourhoods as thick smog blanketed the area.
However, the attempt—the first in 53 years—was “not completely successful” due to insufficient moisture in the air.
Over the last two weeks, Delhi’s Air Quality Index (AQI), which measures fine particulate matter (PM 2.5) harmful to the lungs, has stayed between 300 and 400—almost 20 times the safe limit.
On Tuesday, authorities deployed a Cessna aircraft to release fire flares containing silver iodide and sodium chloride into the atmosphere.
In a statement, IIT Kanpur said that despite the lack of rain, the trial caused a measurable reduction in particulate matter, “indicating that even under limited moisture conditions, cloud seeding can contribute to improved air quality.”
However, the institute’s director Manindra Agarwal told BBC Hindi that this cannot serve as a long-term solution for Delhi’s persistent pollution.
"One measure of success is if it rains, which certainly did not happen," said Mr Agarwal. "The moisture content in the clouds yesterday [Tuesday] was very low. We will continue our efforts in the near future."
The trial is expected to be repeated in the coming weeks when cloud moisture levels increase, Delhi Environment Minister Manjinder Sirsa told reporters.
Delhi’s first cloud-seeding experiment took place in 1957, followed by another in 1972, according to the Indian Institute of Tropical Meteorology. While those earlier attempts focused on drought management, Mr Agarwal said this was the city’s first homegrown effort to curb pollution through cloud seeding.
The city had also considered cloud seeding in 2023, but the plan was delayed due to pending court approvals. At that time, scientists noted that the technique is costly and has low success rates.
Cloud seeding works by accelerating moisture condensation in clouds. Salt particles act as ice-nucleating agents, allowing ice crystals to form and moisture to condense into rain. But the process depends on adequate cloud moisture and humidity, and doesn’t always succeed.
Climate expert Abinash Mohanty told the BBC in 2023, “We also don't know what its [cloud seeding] effects are because in the end you're trying to alter natural processes and that's bound to have limitations.”
Worldwide, cloud-seeding results have been mixed. China has claimed success in managing rainfall before the Olympics using rockets, cannons, and drones, whereas in the UAE, doubts arose after flooding in Dubai last year.
With inputs from BBC