The Delhi government has resumed cloud-seeding trials to generate artificial rain and combat the city's severe air quality index ahead of Diwali, despite previous experiments facing challenges due to insufficient atmospheric moisture.

The Delhi government has resumed cloud-seeding trials to generate artificial rain and combat the city's severe air quality index ahead of Diwali, despite previous experiments facing challenges due to insufficient atmospheric moisture.

The Delhi government has resumed cloud-seeding trials to generate artificial rain and combat the city's severe air quality index ahead of Diwali, despite previous experiments facing challenges due to insufficient atmospheric moisture.

With the air quality index (AQI) worsening in the national capital ahead of the Diwali fireworks, the Delhi government has once again attempted for artificial rain through cloud seeding trails. The government has already conducted two rounds of cloud-seeding trials near the Indira Gandhi International Airport in the last 15 days. 

Trials were conducted at an altitude of approximately 30,000 metres, significantly higher than the altitude of around 10,000 metres at which cloud-seeding operations were carried out in Delhi last year.

According to sources, more trials are likely to be conducted after Diwali and Chhath. 

What is cloud seeding? 

Cloud seeding is a weather modification technique designed to enhance precipitation—such as rain or snow—by artificially dispersing chemical agents into clouds to encourage cloud droplets to form and fall.

How does it work? 

For rain or snow to fall naturally, microscopic water droplets inside a cloud need something solid to freeze or condense around—known as condensation nuclei or ice nuclei. Cloud seeding introduces these artificial "seeds" directly into cloud layers using aircraft, rockets, or ground-based generators.

As the first step, meteorologists use weather radar and satellite imagery to identify clouds carrying adequate moisture that are underperforming or failing to release rain naturally.

Specially equipped planes fly into or directly above the cloud layer, releasing seeding agents from wing-mounted burners. Agents like silver iodide (AgI) or dry ice are introduced into sub-freezing clouds (below zero degree Celsius). Because silver iodide has a crystalline structure nearly identical to ice, supercooled water droplets rapidly freeze onto these particles, forming ice crystals through nucleation.

Now for the warm clouds, hygroscopic salts like sodium chloride (common salt) or potassium chloride are released into warmer clouds. These particles absorb water vapour avidly, causing tiny moisture droplets to collide and coalesce into larger, heavy raindrops.

Why did the artificial rain technique fail last year? 

The Delhi government first rolled out its cloud-seeding project last year in collaboration with the Indian Institute of Technology (IIT) Kanpur.  Two rounds of trials were conducted in October last year, with eight chemical flares containing silver iodide and sodium chloride released during each operation. However, the experiments did not result in rainfall.

They even released a report claiming that the trials had helped reduce particulate matter levels at the targeted locations despite the absence of rainfall. But the technique was unsuccessful altogether as it could not achieve the desired results. 

The attempt was "not completely successful" due to the lack of moisture in the air. 

Over the past few weeks, Delhi's AQI has become "severe", with quality levels touching 600 in some areas. 

In a statement, IIT Kanpur, on conducting the experiment on October 27, said that despite the lack of rain, there had been a measurable reduction in particulate matter because of the experiment, "indicating that even under limited moisture conditions, cloud seeding can contribute to improved air quality".

Delhi's Environment Minister Manjinder Sirsa told reporters that the trial is likely to be repeated in the coming weeks after the moisture levels in the clouds increase again. 

According to the Indian Institute of Tropical Meteorology, Delhi's first cloud-seeding experiment was carried out in 1957, followed by another attempt in 1972. 

IIT Kanpur director Manindra Agarwal told BBC Hindi that those experiments were aimed at drought management then, and this cannot be a long-term fix for Delhi's air pollution problem. 

However, scientists point out that the process doesn't always work and is dependent on the right amount of moisture and humidity in the clouds to allow for ice nuclei to form.

Globally, cloud seeding exercises have yielded mixed results.

China has boasted about its success in managing rains before hosting the Olympics, with Beijing using rockets, cannons and drones to do cloud seeding.

However, in the United Arab Emirates, questions over the technique were raised, following floods in Dubai last year.

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