Why cloud seeding to create artificial rain has been delayed in Delhi

While Delhi has been considering using cloud seeding to create artificial rain to fight the smog in the capital for two weeks now, things are yet to kick-off. Scientists have been waiting for the right meteorological conditions, namely plenty of clouds and correct humidity levels. Wind speed plays a vital role, too. While it's obviously difficult to predict exactly when atmospheric conditions will fall into place, the buzz is that the operation will take place this week.

For the uninitiated, cloud seeding or weather modification is an artificial way to induce moisture in the clouds so as to cause a rainfall. In this process, either silver iodide or dry ice is dumped onto the clouds by using an aircraft or an artillery gun which leads to a rain shower.

According to The Times of India, the cloud-seeding technology currently available in India can only induce potential pre-existing clouds, hence the delay in launching operations. The idea is to use the artificial rain to clear the toxic air in the capital and provide Delhiites with a much-needed respite.

"The exact date and extent of seeding will depend on cloud formation. Scientists can, however, be ready within 24 hours of getting such a prediction," a senior official from the country's central pollution watchdog, CPCB, told the daily. The environment ministry has already given a formal nod to the CPCB to go with ahead with the project. "If we get enough clouds, scientists from IIT, Kanpur will go for seeding silver iodide and other chemical substances in the clouds to induce rain in the city," the source added.

Here's how it works: The amount of rain that a cloud can produce depends on a balance between the number of ice nuclei inside it and the amount of water available to grow around those nuclei. Clouds often lack naturally occurring ice nuclei so injecting them with silver iodide particles increases their numbers.

Doing so makes the clouds more efficient at generating ice crystals that fall as rain or snow, depending on the temperatures in and beneath the clouds.

This will be the first time that clouds would be seeded in India to battle pollution, although the country has tested the technique on a limited scale using two aircraft for research purposes in the rain shadow region of Solapur in Maharashtra.

Although scientists are hopeful that the seeding will take place this week, without adequate cloud formation in the next few days, things may get further delayed.