Is artificial rain the answer to Delhi’s air crisis?

Delhi and its neighbouring cities are gripped by severe pollution. The air quality index (AQI) has touched roughly 500 at certain places, as the city’s residents struggle to breathe. On Wednesday (November 20), the index remained in the ‘severe’ zone for a third consecutive day in Delhi and the National Capital Region (NCR).

As Delhi chokes, the Aam Aadmi Party (AAP) government is seeking to use artificial rain to bring some relief from the noxious pollution. Delhi Environment Minister Gopal Rai on Tuesday wrote a letter to the Centre asking for its nod to allow artificial rain in the region.

“ Delhi is under GRAP (Graded Response Action Plan) Stage IV restrictions, and we are taking every possible step to reduce vehicular and industrial pollution. Restrictions have been imposed on private vehicles and trucks, aiming to curb the number of vehicles entering the city. We are consulting specialists to explore measures to reduce the smog. One of the solutions under consideration is artificial rain, which can help settle pollutants and clear the air,” Rai said at a press conference.

He also urged the Central government to convene a meeting with experts from the Indian Institute of Technology (IIT) Kanpur on the issue.

Does artificial rain really alleviate pollution? Let’s understand.

What is artificial rain?

Artificial rain, or cloud seeding, is a weather modification method to create rain or snow.

In cloud seeding, clouds are usually injected with salts like silver iodide, potassium iodide, or sodium chloride to induce condensation.

For this, meteorologists need to identify clouds for seeding. These clouds must have sufficient moisture but are unable to produce enough precipitation on their own.

M Rajeevan, former secretary of the Ministry of Earth Sciences, told Indian Express earlier, “Cloud seeding can only happen if there is a sufficient number of clouds and a particular depth to these clouds. Inside, there needs to be an adequate number of cloud droplets. Cloud seeding is done to increase the radius of the cloud droplets so that they will grow bigger and because of gravity, they will come down as rainfall. But with a clear sky, you can’t do it.”

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The salts, or the seeding agents, serve as nuclei around which water droplets can form or ice can crystallise. These particles are dispersed into clouds using special aircraft, rockets, or dispersion devices kept on the ground.

As water droplets grow, they collide with others in the cloud. As they become heavy, the cloud gets saturated and it rains.

Does artificial rain work against pollution?

The effectiveness of artificial rain is still a matter of debate.

Artificial rain helps clear pollutants and dust from the air. Fine particulate matter (PM 2.5) and PM10 get washed away with prolonged precipitation. However, there is no impact on other pollutants such as ozone and sulphur dioxide.

Sachchida Nand Tripathi, Dean of Kotak School of Sustainability at IIT Kanpur, told NDTV that tackling air pollution with artificial rain will not be easy. “When you already are in such a critical situation with such episodic pollution, artificial rain cannot be experimented or tried now…doing it at this point in time won’t help much. It requires a lot of experimentation”.

“It is going to be very difficult, given all the clearances it requires and the optimal weather conditions, the probability of it working is very low,” he added.

According to IIT Kanpur’s Manindra Agrawal, artificial rain could provide relief to NCR residents for a week from deteriorating air quality, reported Business Standard.

In India, cloud seeding was carried out in Maharashtra’s Solapur over two monsoons in 2018 and 2019. The findings of this experiment were published in the Bulletin of the American Meteorological Society last year, revealing that the city witnessed 18 per cent more rainfall than normal conditions.

“Not all clouds are seedable, not all clouds will make rain. There are clouds that will get dissipated on seeding. Overall, however, there was a net increase of 18 per cent [rainfall] in a 100 square km area. Our experiment was very controlled and we selected clouds based on their potential to make rain,” Dr Thara Prabhakaran, the lead scientist for the experiment, told The Hindu in 2023.

She said carrying out cloud seeding in the pre-monsoon or post-monsoon period could have different results.

Aerosol scientist Shahzad Gani wrote for Indian Express last year that artificial rain can only bring temporary respite from pollution.

Its impact on the environment has also raised concerns, including introducing chemicals into the atmosphere. The seeding agents, such as silver iodide, could affect the environment if they accumulate in soil and water in large quantities.

As Gani wrote for Indian Express, there are also ethical concerns about using artificial rain to combat pollution.“The water vapour used in the process would have naturally precipitated elsewhere, and it potentially deprives other regions of rainfall. This artificial manipulation of weather patterns could even lead to droughts in areas which would have received this rainfall otherwise,” he said in the piece.

Experts suggest it is better to focus on curbing emissions and strictly implementing pollution control measures than relying on such methods.

With input from agencies