Explained: What Is Cloud Seeding, Why Is Delhi Spending Over Rs 3 Crore On It

Delhi is set to launch its first-ever cloud seeding trial from July 4 to 11 to combat its persistent air pollution through artificial rain.

Announced by Environment Minister Manjinder Singh Sirsa, the Rs 3.21 crore project will deploy modified Cessna aircraft to disperse a scientifically formulated mix of silver iodide nanoparticles, iodised salt, and rock salt into moisture-laden clouds over northwest and outer Delhi, with the aim of triggering rainfall and cleansing the air.

Coordinated by IIT Kanpur and IMD Pune, the operation is a historic first for the capital and will cover 100 sq km in each of the five 90-minute sorties. 

What Is Cloud Seeding?

Cloud seeding is used to make it rain or snow by adding special substances such as silver iodide or salt to clouds. It can be done using airplanes, rockets, or machines on the ground.

Cloud seeding is used in many countries (China, US, UAE) to help with droughts, increase snowfall, reduce hail, clear fog, or improve air quality. It usually works only when there are already clouds in the sky and can increase rainfall by about 5-15 per cent.

How Cloud Seeding Works

Cloud seeding works by adding certain substances into clouds to encourage the formation of raindrops or snowflakes. These substances, like silver iodide, potassium iodide, dry ice, or salt, act as "nuclei" that attract water vapour. When water vapour gathers around these particles, it condenses into larger droplets or ice crystals. Once these droplets or crystals become heavy enough, they fall to the ground as rain or snow.

There are two main types of cloud seeding: cold cloud seeding, where silver iodide helps ice crystals form in supercooled clouds (below 0 degrees Celsius), and warm cloud seeding, where salt particles help small droplets combine into larger raindrops. 

Is Cloud Seeding Effective?

Cloud seeding is generally considered moderately effective, with studies and real-world programmes showing it can increase rainfall or snowfall by about 5-15 per cent under the right conditions.

In places like the western United States and Australia, cloud seeding has been used successfully to boost snowpack and water supply, with some projects reporting gains of up to 14 per cent. Results vary depending on the method, weather conditions, and region.

For example, in India, a pilot project saw only a 3 per cent increase in rainfall. The technique works only if suitable clouds already exist and is most effective in moisture-rich or supercooled cloud systems.