Delhi seeds clouds to clear post-Diwali smog, but rain still elusive

Despite high levels of air pollution in the national capital, experts say artificial rain is both expensive and only temporary fix, and that cities must tackle primary sources

The Delhi government on Tuesday carried out another cloud-seeding attempt to induce artificial rain, using an aircraft from Kanpur that dispersed eight fire flares over Burari, Karol Bagh, and Mayur Vihar during a half-hour operation before landing at Meerut airfield. The Indian Institute of Technology Kanpur (IITK), which is overseeing the exercise, said rainfall could occur within 15 minutes to four hours.

 

However, the cloud-seeding attempt did not lead to rainfall.

 

According to scientists, Tuesday marked Delhi’s third attempt at artificial rain. The first was conducted during the 1957 monsoon, and the second in the early 1970s. At that time, the understanding of cloud seeding was still rudimentary.

 

The India Meteorological Department had predicted light rain for Tuesday morning and later in the week, weather conditions favourable for the formation of clouds suitable for seeding.

 

Tuesday’s operation was the Delhi Bharatiya Janata Party government’s second attempt. The first, conducted last week over Burari using small quantities of silver iodide and sodium chloride, failed to produce rain because of low atmospheric moisture — less than 20 per cent compared to the 50 per cent typically required.

 

“A Cessna aircraft took off from Kanpur and released eight fire flares, each weighing 2 to 2.5 kilograms. The trial lasted for half an hour; each flare burnt for two to two and a half minutes. The clouds had a humidity of 15 to 20 per cent. The flares were released for about 17 to 18 minutes,” Environment Minister Manjinder Singh Sirsa said in a video statement.

 

The Delhi government claimed the artificial rain would help wash away the after-Diwali smog, which thickened after residents ignored in defiance the Supreme Court’s firecracker restrictions on both type and timing.

 

The Delhi government signed a memorandum of understanding with IITK on September 25 to conduct five cloud-seeding trials, all planned in northwest Delhi.

 

The Directorate General of Civil Aviation earlier granted permission to IITK to conduct the trials anytime between October 1 and November 30.

 

Clearances have also been secured from more than 10 central and state departments, including the Union ministries of environment, defence, and home affairs; the Uttar Pradesh government; the Airports Authority of India; and the Bureau of Civil Aviation Security, among others.

 

The Delhi Cabinet on May 7 approved a proposal to conduct five cloud-seeding trials at a total cost of ₹3.21 crore.

 

Some experts, however, question the effectiveness of cloud seeding as a sustainable way to curb air pollution. They argue it is, at best, a temporary fix, since pollution levels inevitably return once the rain stops. Instead, they say, the government should focus on the main sources of pollution rather than rely on short-term measures like artificial rain.

 

Making clouds sweat

 

Cloud seeding is a technique that uses microscopic cloud-forming particles to increase rainfall, according to the Pune-based Indian Institute of Tropical Meteorology (IITM).

 

This can be done in two ways: hygroscopic and glaciogenic.

 

In the first method, seeding is done at the base of warm clouds using particles that attract water vapour. The glaciogenic method is used in cold clouds by seeding near the top with silver iodide pellets, which help form ice particles that later turn into rain.

 

Hygroscopic seeding was first attempted in India in the 1970s by IITM. Since then, states such as Maharashtra and Karnataka have occasionally experimented with artificial rain, but with limited success.

 

During the monsoon season, hygroscopic (cloud-base) seeding tends to be more effective since the clouds already contain higher moisture content.

 

The chemistry of fake rain

 

Madhavan Rajeevan, former secretary of the Ministry of Earth Sciences and a key figure behind several cloud-seeding experiments, explained that the most common method involves spraying chemicals at the base of clouds using aircraft.

 

“The clouds are spotted using radars, and once one is identified, the pilots are informed. They immediately fly to the cloud base and pump in the chemicals,” Rajeevan said.

 

As rising air pushes the chemicals into the cloud, droplet formation begins.

 

Cold clouds, which typically hold supercooled liquid water, are injected with silver iodide, prompting the water to attach to it and form snowflakes that later melt into rain.

 

Warm clouds — which contain tiny water droplets too small to coalesce naturally — are seeded with sodium chloride (salt), which draws moisture and helps create larger drops.

 

But here’s the catch: there must already be moisture-laden clouds for seeding to work. Without that, the process cannot even begin.

 

World’s been at it — India’s catching up

 

Last year, IITM released findings from a two-year study — published in the Bulletin of the American Meteorological Society — testing the feasibility and effectiveness of cloud seeding.

 

Cloud seeding is now practised in more than 56 countries, including Australia, China, Russia, Thailand, the United Arab Emirates, and the US, primarily for weather modification and rainfall enhancement, according to an IITM report.

 

In India, results have been mixed.

 

The experiments were part of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-IV, with earlier phases conducted in 2009, 2010–11, and 2014–15. Phase-IV was carried out in Solapur, Maharashtra, during the summer monsoon months of 2018 and 2019.

 

The report found that during CAIPEEX-IV, rainfall increased by up to 46 per cent in some areas, and by an average of about 18 per cent across a 100-square-kilometre stretch in Solapur’s rain-shadow region — roughly 8.7 millimetres of extra rain, enough to justify the experiment in cost-benefit terms.

 

Between 2017 and 2019, IITM scientists evaluated 276 clouds using a network of automatic rain gauges, radars, radiometers, and aircraft.

 

The report observed “robust statistical significance above a 95 per cent confidence level” and said the experiment helped document cloud and rainfall processes and develop seeding protocols.

 

CAIPEEX began in 2009 (Phase-I), followed by 2010–11 (Phase-II), 2014–15 (Phase-III), and 2017–19 (Phase-IV). The first three phases involved research and airborne cloud observations that laid the groundwork for Phase-IV’s seeding trials.

 

The findings suggest that cloud seeding can be an effective strategy for enhancing rainfall in the right conditions.

 

A short fix for a long crisis?

 

Rajeevan cautioned that cloud seeding can produce rain only for a few days and cannot ensure that pollution won’t return. “Also remember: not every seeded cloud will produce rain,” he said. “My advice would be to target the real sources of urban pollution — vehicles and factories — instead of short-term fixes like cloud seeding.”

 

Himanshu Thakker, coordinator of the South Asia Network on Dams, Rivers and People, echoed the sentiment. He said cloud seeding is a temporary measure and that efforts should focus on addressing pollution at its source.

 

The price of playing rainmaker

 

IITM’s cloud-seeding experiment reportedly cost around ₹200 crore. Officially, the report pegged the operating cost at about ₹15 lakh per seeding flight.

 

While the study confirmed the effectiveness of cloud seeding under specific conditions, its cost-benefit analysis estimated the price of producing water through the process at about 18 paise per litre.

 

By comparison, reports suggest the Brihanmumbai Municipal Corporation spends around ₹19.44 per 1,000 litres of water supplied to residents — about ₹0.019 per litre — far cheaper than cloud-seeded rain.