Cloud seeding is a technique to induce precipitation (rain or snow) by dispersing suitable chemicals into clouds. The result can be encouraging if the clouds targeted contain enough water vapour.
The commonly used chemicals for seeding include silver iodide, potassium iodide, dry ice (solid carbon dioxide), liquid propane and table salt (sodium chloride).
Substances like silver iodide, which has crystalline structure, cause freezing nucleation in clouds. It may also help initiate other microphysical processes in clouds. As a result, tiny water vapour particles grow large and heavy enough to fall as rain drops or snowflakes.
Seeding chemicals may be dispersed by aircraft or from the ground by firing up rockets or similar devices such as anti-aircraft guns. Silver iodide flares can also be released by aircraft flying through clouds.
China has extensively experimented with cloud seeding by firing silver iodide rockets into clouds for induced precipitation and also to clear air pollution.
In India, cloud seeding experiments were conducted a few times to induce artificial rains by the Tamil Nadu government from 1980s. The Karnataka government also attempted similar efforts two decades later. Maharashtra conducted such operations in the beginning of the beginning of the new century. The Delhi government now plans to try the method to combat frequent smog and persistent air pollution.
Some other countries that tried to manipulate precipitation through seeding include Indonesia, Thailand, Kuwait, UAE, USA, Canada, France, Russia, Germany, Australia, and some African countries.
Experts and research show that silver iodide used for cloud seeding may cause negligible health hazards to humans and almost no environmental hazards.