As Delhi readies for artificial rain, here’s all about the science of cloud seeding

After implementing the odd-even vehicle scheme, switching to online classes, and following Stage IV of the Graded Response Action Plan (GRAP), the Delhi government is now considering a spell of artificial rain to deal with the ‘severe’ air pollution in the national capital.

If all goes well, Delhiites will get drenched in artificial rainfall on November 20-21 and get relief from the health hazards that are plaguing them, thanks to the relentless stubble-burning in the neighbouring Punjab and Haryana, barring local factors like vehicular pollution.

Besides, after Diwali on November 12, the national capital’s air quality is expected to take a turn for the worse. But what is artificial rain? How easy will it be for Delhi to get a spell of artificial rain? Here is all about this unique concept.

What is artificial rain?

The process by which artificial rain is induced is called cloud seeding. It is basically a scientific process by which certain chemicals are released into clouds to enhance their ability to make rain or snow. Experts also call the process “weather modification”.

How is cloud seeding done?

There are two main ways to do cloud seeding. One is to release the chemicals from below the cloud. A plane with the chemicals concerned flies below moisture-laden clouds, and flares on the plane’s wings burn the chemicals from below. The updraught takes the particles high into the cloud for the “seeding”.

In the second method, the chemicals are dropped from above the cloud. The flares are dropped from the plane in this case and they catch fire once they fall off the plane and on to the cloud, thus “seeding” the cloud with the particles.

How does cloud seeding work?

It’s common knowledge that not all clouds make rain. But why is that so? One reason is that a cloud may not have enough ice particles or enough cloud droplets to combine and make raindrops.

Cloud seeding gives such moisture-laden clouds more ice crystals to help for bigger droplets to combine and make rain. Some of the common chemicals used for cloud seeding are silver iodide, dry ice (solid carbon dioxide), and potassium iodide. The particles of these compounds serve as nuclei around which water droplets can form, leading to the creation of raindrops.

Silver iodide is preferred because its structure resembles that of natural ice crystals. When a cloud is seeded with silver iodide, its crystals grow quickly once exposed to the cloud’s moisture. The crystals swiftly turn into heavy, large raindrops. Only 1 g of silver iodide can reportedly create up to 10 trillion artificial ice crystals.

How long does cloud seeding take?

The process usually takes around half an hour.

Is success guaranteed?

Not necessarily. To begin with, moisture-laden clouds must already be present in the sky and wind patterns must be suitable.

For instance, IIT Kanpur, which has proposed artificial rain for Delhi, has said that a minimum of 40 per cent cloud cover is necessary to create artificial rain, Delhi Environment Minister Gopal Rai has said. November 20-21 has been chosen because there is a possibility of a cloud cover over Delhi at that time.

How long will the effects last?

Manindra Agrawal, a professor in the computer science and engineering department at IIT Kanpur, told The Economic Times that artificial rain can provide only temporary relief, for up to a week.

Has IIT-Kanpur done it before?

IIT-Kanpur has been working on this project since 2018, says the ET report. After five years, the institute reportedly conducted successful trials in July this year.

So, are the skies clear for Delhi to carry out cloud seeding?

No. The process needs several approvals before Delhi can go ahead with it. To begin with, the Delhi government has asked the IIT team for a detailed plan, which it will submit in Supreme Court on Friday (November 10).

If the Supreme Court gives its consent, the Delhi government and the Centre will move on to the next steps. Permission has to be received from the Directorate General of Civil Aviation (DGCA), the Home Ministry, and the Special Protection Group responsible for the Prime Minister’s security.

Objectives of cloud seeding

Combating drought and its effects on agriculture, securing drinking water supply, fighting forest fires, and preventing hailstorms are some of the reasons why cloud seeding is used. Delhi is, of course, seeking to combat pollution.

Successful cloud seeding by other countries

China reportedly uses cloud seeding on a regular basis. Every Chinese city reportedly has a local cloud-seeding plan, which officials and researchers implement in cooperation with the military. The People’s Daily reported that between June and November 2022, cloud seeding brought about “8.56 billion metric tons of additional rainfall” in the Yangtze basin.

The US, the UAE, Russia, Saudi Arabia, France, South Africa, Thailand, and Mexico have also developed the method.