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Can cloud-seeding really wash away Delhi’s pollution? Experts say no. The technology’s success rate remains highly uncertain, and even when it works, the scale of rainfall is too small to make a measurable difference. “You’re spending crores for a drizzle,” says one environmental expert.
But the Delhi government is trying anyway, desperate to scrub the skies clean. The city government has just sent planes into the air in the hope of coaxing raindrops down upon the heads of the city’s millions.
On Tuesday, two small aircraft released flares containing silver iodide and other particles into clouds at altitudes of about 4,000 to 5,000 feet. The targeted area was roughly 46 kilometres long and 7 kilometres wide over northwest Delhi.
Officials insisted the trials were a success, claiming there was light rainfall in parts of Noida a few hours after the flights. They also conceded that the weather conditions were not ideal for cloud seeding as the clouds lacked sufficient moisture.
The government’s experiment comes amid an annual pollution crisis that worsened dramatically after the city went cracker-crazy during Diwali. Fireworks pushed Delhi’s Air Quality Index from 175 (“unhealthy”) on October 15 all the way to 334 (“very poor”) on October 21, and over 400 at many of the city’s monitoring stations that night thanks to frenzied cracker-bursting.
What is worse is that the choking pollution has lingered at sky-high levels with no sign of improvement.
Delhi’s BJP chief minister Rekha Gupta, who was catapulted into the city government’s top slot in February, is eager to show she can outperform her predecessor, Aam Aadmi Party (AAP) leader Arvind Kejriwal, in tackling the city’s toxic air. So she is looking to wrestle down the pollution numbers in any way possible and has turned to dramatic fixes like cloud seeding.
What is wrong with cloud seeding? The answer, scientists say, is just about everything. Cloud seeding is neither precise nor predictable. The process involves dispersing substances such as silver iodide into clouds to encourage condensation and rainfall.
However, its success depends entirely on having the “right kind” of clouds. They need to be moisture-laden and extend at least a kilometre in height.
Another key question for Delhi is whether cloud seeding can work in this giant metropolitan sprawl. Delhi stretches over 1,484 sq km, and the National Capital Region is a vast urban area that covers 55,083 sq km of the northern Indian plain. It includes cities like Gurugram, Noida, Faridabad, Ghaziabad and Meerut.
The flights that took off Tuesday could only fly over a limited area.
“If it rains in 5 sq km, that will make no impact,” says Mohan P. George, clean air and mobility consultant at the Centre for Science and Environment. He adds: “The technology is not so calibrated. It may rain in Delhi or in Ghaziabad or Meerut. Also, financially you can’t do it.”
He continues: “If it does rain, there may be some effect. But once again the question is how much rain you are having. If it’s just a slight drizzle here or there, it may complicate things more.”
Drizzle-sized droplets are too small to wash pollutants out of the air. Instead of clearing the pollution, they can just move it closer to the ground, making the air worse for people to breathe. Also, after a light drizzle, the air near the ground cools while the air above stays warmer, creating a lid that traps pollution and makes smog last longer.
Meteorologists point out that post-monsoon skies over north India rarely contain the kind of moisture-laden clouds required for effective seeding. George notes that such clouds must “contain an adequate amount of water vapour and liquid water” to produce rainfall at all. “It’s crucial to have what can only be called the right type of cloud,” George says.
The thick grey pollution haze that now blankets Delhi in winter arrived late this year, largely because the monsoon continued much longer than usual until about October 10. As a result, the city had more clear days than it usually has enjoyed in recent years.
But the blue skies suddenly vanished under a cloud of smog after the Supreme Court gave the go-ahead to what were optimistically described as “green crackers”.
In practice, there were no checks on whether the fireworks being set off were actually “green”, and even these supposedly cleaner versions still release dangerous PM2.5 and PM10 – tiny particles of dust, soot and smoke that are small enough to be breathed deep into the lungs, causing respiratory and heart problems, with PM2.5 fine enough to enter the bloodstream.
The Diwali firecrackers, compounded by exhaust fumes from millions of vehicles and industrial emissions, filled the skies with the familiar yellow-grey smog.
What is even worse is that the smog haze right now is generated by Delhi emissions alone. Crop burning in Punjab, which normally worsens Delhi’s air each November, has not yet peaked.
“The pollution haze is purely generated over Delhi and its surrounding areas,” George explains. “Farming is only contributing 2 per cent to 3 per cent of Delhi’s pollution woes currently.”
There is another very big catch with cloud seeding: the sheer cost of putting aircraft in the air and having them fly around seeding the clouds. The Delhi government teamed up with IIT Kanpur for the project, using a Cessna 206H aircraft to fire the flares.
Tuesday’s two flights were only the beginning – three more are planned. The total price tag: about Rs 3.2 crore.
Cloud seeding has a long history of letting people down. The first “success” in 1946 triggered a tiny snow shower in Massachusetts, and early trials in Denver the following year, when scientists released dry ice into clouds, produced some localised snowfall but that was about it.
Since then, attempts around the world, from Australia and California to Pakistan and China, have frequently failed to produce meaningful rainfall, shifted precipitation to the wrong areas, or delivered results too small to matter. Experts warn that cloud seeding is often little more than an expensive gamble.
Pakistan conducted trials with UAE support in 2023 with minimal measurable impact, while India has tried similar efforts in Vidarbha, Tamil Nadu and Karnataka without clear or consistent results.
The skies over Delhi are clouded with politics as much as pollution. The city’s BJP government has accused Punjab’s AAP of encouraging farmers to burn crop stubble and worsen Delhi’s air, while AAP leaders counter that Gupta’s government is indulging in “gimmicks” to distract from its own failures.
Whatever the political blame game, the data tell their own story: Delhi has again claimed the title of the most polluted city in the world, followed closely by Lahore across the border.
Climate scientists say cloud seeding may occasionally work to induce rainfall, but it is no solution to pollution. Even if the experiment triggers showers over a small pocket of the city, the effect on overall air quality would be negligible.
In the end, as experts say, there is no quick fix for Delhi’s toxic skies. Clearing the air will take long-term investment, far stricter enforcement of emission norms and cleaner transport, not a few drops of artificial rain.
