Despite inputs from the India Meteorological Department (IMD) that clouds would be insufficient to cause artificial rain over Delhi on October 28, researchers at the Indian Institute of Technology, Kanpur, went ahead. His plan to fly a Cessna plane And to break the clouds, 10 kg mixture of silver iodide, common salt and rock salt was poured into the clouds. twice. And failed both times.
That Tuesday – when Delhi’s air quality was predictably ‘poor’ – it was the first time the capital had experimented with cloud-seeding since 1972 and, for the first time, with an express plan to improve air quality.
“We shared information with them (IIT-Kanpur) on the state of clouds, but did not give any specific input on whether they should go ahead with cloud seeding or not,” said a senior scientist in the Ministry of Earth Sciences (MoES). The Hindu“We did not give any advice because the Indian Institute of Tropical Meteorology (IITM), Pune, has conducted several cloud seeding experiments over the years and there is still no solid evidence that it works reliably. We did not make any recommendations but shared our input regarding clouds, which was that there were no clouds.”
IMD Director General M. Mahapatra confirmed this The Hindu However, the cloud inputs were “shared”, underscoring that this information was common. “Cloud and humidity information is available to anyone,” he explained.
Manindra Aggarwal, director of IIT-Kanpur and the public-facing officer of the institute’s programme, said his team had earlier held talks with “IITM and IMD”, but their response was “negative” and “it (cloud-seeding for winter pollution) will not work.” IIT-Kanpur has considerable expertise, influence and resources in scientific fields across India, with many of its faculty involved in a number of central and state (Delhi) projects, including air quality issues, and hence partnering with institutes for collaborative research is not new.
The institute does not have an atmospheric sciences department, but does have an aerospace programme, Mr Agarwal said, and the specific program is led by Dr Deepu Philip, professor in the department of management sciences. It also included experts from the Department of Chemistry and Aerospace.
“But it works,” Mr Agarwal told The Hindu“It may not work in India, but it has worked in China and the UAE,” Mr Aggarwal said, adding that the decision to go ahead with the trial despite IMD’s forecast for unfavorable clouds was deliberate, as the team wanted to test the efficacy of its “proprietary solution”, which was “20% silver iodide, rock salt and common salt” with flares manufactured in Sivakasi, Tamil Nadu. “We knew that there was less than 15% moisture (cloudiness) which is too low for seeding. However, we needed data to ascertain the potency of our indigenously produced salt mixture.
Cloud seeding, or the spraying of fine chemical aerosols into clouds to induce rain, has been a subject of investigation in India for decades and the recognized authority on the subject – IITM, Pune – has conducted careful experiments since 2009 on the effectiveness of cloud seeding in enhancing monsoon rainfall.
While India’s state governments have in the past employed private companies for seeding when their areas faced drought, the results were unsuccessful; Because, it is impossible for technology to create rain clouds. The underlying rule of cloud seeding is that it can help add more water to clouds with only a minimal amount of water vapor, called ‘warm clouds’.
But if there is already water vapor in the clouds, they will rain. So what is the benefit of sowing seeds?
IITM-CAIPEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) was designed to answer this. Just as medical researchers test new drugs in randomized clinical trials, with one group of participants receiving one drug and another drug only assuming they have consumed one drug and then evaluating whether the health outcomes of actual recipients are improved, CAIPEX researchers flew tubes of chemical powder attached to the wings of planes at the base of selected hot clouds over Solapur, Maharashtra – a rainfall and water-scarce region. They chose exactly 276 hot clouds – the same as the 276 patients – and seeded 151, leaving the rest – 125 – unseeded.
These clouds were selected through a series of radar (to observe cloud characteristics) and rain-gauge (to record rainfall) during the monsoon months of 2018 and 2019. With this information, the researchers were able to send aircraft to the desired clouds to sow seeds – each flight cost ₹15 lakh. This revealed that half of the seeded and about 70% of the unseeded clouds ‘died’ without producing any rain. About 40% of seeded clouds gave rainfall and 27% of non-seeded clouds gave rainfall.
Overall, seeded clouds delivered an average of 46% more rainfall at seeded locations than at unseeded locations. More than 100 square km. Downstream in the region, unseeded clouds produced 18% more rainfall than seeded clouds. This was determined after chemical analysis of water on rain gauges, which showed how much water came from seeded versus unseeded clouds.
Conclusion: Warm-cloud seeding was only suitable for enhancing monsoon rainfall. There is a whole list of warnings such as sowing seeds only after choosing the right clouds; Using only calcium chloride for seeding at the base of clouds; There should be a radar and gauge system; And specific types of clouds are to be targeted. The results of these experiments as well as a detailed FAQ are available on the IITM website.
Given the Delhi government’s history of taking tough measures ranging from smog towers to banning select cars based on license plates, the possibility of using cloud-seeding to clean up smog-filled air has been under discussion for at least seven years. Unlike the CAIPEX scenario, this involves seeding outside the monsoon months, when all-important warm clouds are largely absent.
For at least seven years, the Delhi government’s cloud-seeding proposals have been torpedoed by the Centre. The scientific consensus of a group of experts including IITM and IMD has been consistently and last expressed in response to a parliamentary question in the Rajya Sabha in December 2024: “Effective cloud seeding requires specific cloud conditions, which are generally absent during the cold and dry winter months of Delhi. Even if suitable clouds were present, the dry atmospheric layer beneath them could evaporate any developed precipitation before it reaches the surface. Additionally, there are uncertainties, efficacy and, potentially There are concerns about adverse effects of cloud seeding chemicals,” Union Minister of State for Environment Kirti Vardhan Singh had said.
Mr Aggarwal acknowledges that the post-monsoon and winter months (October-February) generally do not see moisture-laden clouds capable of producing enough rain to clear the air. However, he disagrees that the practice is wasteful. “On the other hand, IMD data shows that on an average 4-5 western disturbances (storms coming from the Mediterranean Sea that bring rain to North India) occur during this season. These carry moisture-laden clouds. If we seed once in 10 days and we can reduce the air quality index by a reasonable amount, say, for three days, won’t that reduce the pollution impact by 30%? That’s a win.”
Since WD will naturally reduce pollution, why is seeding necessary? To this his reply was that “sowing will only increase the rains, and the more rains, the better.” So in his view, as an experiment, it is definitely worth pursuing. According to his estimate, conducting cloud seeding in Delhi during the winter months would cost ₹30 crore (assuming the periodic seeding schedule proposed by him). “This is a drop in the overall budget to reduce Delhi pollution.” Mr Aggarwal said IIT-Kanpur has got the green signal for more trials this season thanks to “encouragement” from Delhi Environment Minister Manjinder Singh Sira.
According to public estimates, CAIPEX planned 103 flights as an experiment during 2017–2019, each costing ₹15 lakh or about ₹15 crore in total. The fixed one-time cost of setting up the infrastructure (radar, rain gauge, radiosondes, etc.) was ₹33 crore, which included ₹5 crore annually as maintenance cost. To be sure, practical seeding operations conducted commercially would average four hours per seeding operation or about ₹60 lakh per operation.
There are variable flight costs. IITM had earlier said it could halve the cost if it had its own aircraft. IIT-Kanpur has an aircraft — “a significant advantage,” Dr. Aggarwal said.
“There is zero data on cloud seeding in Delhi during the winter months and what we are doing is establishing a baseline. The data analysis is still ongoing but initial reports suggest that there was marginal improvement in air quality in parts of Delhi NCR. There was zero wind that day. It is very less but definitely something. We are not re-inventing the wheel; it does not exist.”
The CAIPEX experiments had a different component: seeding 31 ‘glaciogenic’ or ‘cold clouds’ (those containing both ice and water) and comparing them with 31 unseeded cold clouds in Solapur. The result was that both types of clouds brought rain but not at the sowing site. Their report states, “Glaciogenic cloud seeding redistributed precipitation over a wide area, and had a non-obvious effect on precipitation at the CAIPEX experimental location.”
Dr Aggarwal said he was not aware that the IIT-Kanpur experiment targeted cold clouds, but historical cloud seeding experiments have used silver iodide – a substance that can be toxic – to create ice. IIT’s Cessna aircraft cannot climb to an altitude of more than three kilometers, making it impossible for them to reach cold clouds, which are generally higher in altitude and must be seeded from above the cloud rather than below.
“The seeding mix used includes both materials – nano-particle AgI (silver iodide) is primarily a glaciogenic seeding material, while micro-sized rock/sea salt is a hygroscopic material. We dispersed the mixture using flares at the base of clouds (warm clouds) – so the dispersal mechanism is hygroscopic seeding,” Mr. Philip said in a text message.
“The challenging part of cloud experiments is to determine how much of the salt mixture can actually be used to form water crystals, which can then grow. This requires a lot of ground studies in places called cloud chambers. Too much seeding is as counterproductive as too little seeding,” said the scientist attached to the Ministry of Earth Sciences.
