On October 28, despite clear warnings from the India Meteorological Department (IMD) that Delhi’s clouds were inadequate for artificial rain, researchers from IIT-Kanpur proceeded with their cloud-seeding experiment. Their plan involved two attempts to release 10 kilograms of a silver iodide, common salt, and rock salt mixture from a Cessna plane, aiming to induce rainfall. Both attempts were unsuccessful.
This particular Tuesday, with Delhi’s air quality predictably ‘poor’, marked a significant first: it was the capital’s inaugural cloud-seeding attempt since 1972, and the very first time such an effort was explicitly aimed at improving air quality.
A senior scientist from the Ministry of Earth Science (MoES) clarified that while cloud data was shared with IIT-Kanpur, no specific advice was given on proceeding with the seeding. ‘We didn’t recommend it because the Indian Institute of Tropical Meteorology (IITM), Pune, has conducted numerous cloud-seeding experiments over the years without finding reliable evidence of its consistent effectiveness,’ the scientist stated. ‘We simply provided information on the cloud conditions, which clearly indicated an absence of suitable clouds.’
M. Mohapatra, Director-General of the IMD, confirmed that general cloud data was shared, emphasizing that ‘information on cloud cover and humidity is publicly accessible.’
Manindra Agrawal, Director of IIT-Kanpur and the program’s spokesperson, acknowledged previous discussions with IITM and IMD, noting their ‘negative’ feedback and skepticism that ‘cloud-seeding for winter pollution wouldn’t work.’ IIT-Kanpur, known for its scientific expertise and involvement in various air quality projects across central and state levels, often collaborates on research initiatives.
Mr. Agrawal mentioned that while the institute lacks an Atmospheric Sciences department, it possesses an aerospace program. This specific cloud-seeding project was spearheaded by Dr. Deepu Philip, a Professor in the Department of Management Sciences, with additional experts from the Chemistry and Aerospace departments contributing.
Defending the initiative, Mr. Agrawal stated, ‘It does work, perhaps not yet in India, but it has shown success in China and the United Arab Emirates.’ He explained that the decision to proceed with the trial, despite the IMD’s unfavorable cloud forecast, was intentional. The team aimed to test their ‘proprietary solution’ – a mix of 20% silver iodide, rock salt, and common salt, with flares produced in Sivakasi, Tamil Nadu. ‘We knew the clouds had less than 15% moisture, which is insufficient for effective seeding. However, gathering data on our locally developed salt mixture’s potency was crucial,’ he added.
Cloud seeding, the process of dispersing chemical aerosols into clouds to stimulate rainfall, has been a long-standing area of research in India. Since 2009, the Indian Institute of Tropical Meteorology (IITM) in Pune, recognized as a leading authority, has conducted extensive experiments to assess its efficacy in boosting monsoon rains.
Historically, Indian State governments have enlisted private firms for cloud seeding during droughts, but outcomes have been inconsistent. This is largely because technology cannot conjure rain clouds out of thin air. The fundamental principle of cloud seeding dictates that it can only enhance existing ‘warm clouds’ that already possess minimal water vapor.
This raises a critical question: if clouds already contain enough water vapor to rain, what benefit does seeding provide?
The IITM-CAIPEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) was specifically designed to explore this very question. Similar to how medical researchers conduct randomized clinical trials, CAIPEX researchers attached tubes of chemical powder to plane wings and released them into the base of selected warm clouds over Solapur, Maharashtra, a drought-prone area. They identified 276 warm clouds and seeded 151 of them, leaving the remaining 125 untouched for comparison.
Conducted during the monsoon seasons of 2018 and 2019, clouds were selected using radar for characteristics and rain gauges for measurement. This data guided aircraft, with each mission costing ₹15 lakh, to the target clouds. The results showed that half of the seeded clouds and almost 70% of the unseeded ones dissipated without rain. Approximately 40% of seeded clouds produced rain, compared to 27% of unseeded clouds.
Ultimately, seeded clouds generated an average of 46% more rain at the treated locations compared to their unseeded counterparts. Furthermore, a 100 sq.km. area downwind experienced an 18% increase in rainfall from seeded clouds versus unseeded ones. This was confirmed through chemical analysis of rainwater collected by gauges, distinguishing water originating from seeded clouds.
The CAIPEX experiments concluded that warm-cloud seeding is effective solely for augmenting monsoon rainfall. This process comes with several strict conditions: careful selection of suitable clouds, exclusive use of calcium chloride for seeding the cloud base, implementation of a comprehensive radar and gauge system, and precise targeting of specific cloud types. Detailed findings and a comprehensive FAQ are published by IITM.
Considering the Delhi government’s past reliance on drastic measures—such as deploying smog towers and implementing vehicle rationing based on license plates—cloud-seeding has been explored as a solution for air pollution for at least seven years. However, unlike the CAIPEX study, which focused on monsoon conditions, these proposals involve seeding outside the monsoon months, a period when essential warm clouds are typically scarce.
For over seven years, the central government has consistently rejected Delhi’s cloud-seeding proposals. The scientific community, including experts from IITM and IMD, has maintained a unified stance, reiterated in the Rajya Sabha in December 2024 by Union Minister of State for Environment Kirti Vardhan Singh. He explained, ‘Effective cloud seeding demands specific cloud conditions, which are typically absent during Delhi’s cold, dry winter. Even if suitable clouds formed, precipitation could evaporate before reaching the ground due to the dry lower atmosphere. Furthermore, uncertainties regarding its efficacy and potential adverse effects of cloud-seeding chemicals persist.’
Mr. Agrawal acknowledged that post-monsoon and winter months (October-February) typically lack the moisture-rich clouds necessary for effective pollution-clearing rainfall. However, he argued against dismissing the effort as futile, citing IMD data indicating 4-5 Western Disturbances—rain-bearing storms from the Mediterranean—occur during this period. ‘These disturbances bring moisture-laden clouds,’ he noted. ‘If we seed once every ten days and achieve a significant reduction in the Air Quality Index for, say, three days, that could translate to a 30% reduction in pollution impact. That would be a considerable victory.’
When questioned about the necessity of seeding if Western Disturbances naturally alleviate pollution, Mr. Agrawal responded that ‘seeding would simply enhance rainfall, and more rain is always beneficial.’ Therefore, he believes the experiment is worthwhile. He estimated that winter cloud seeding over Delhi would cost ₹30 crore for the proposed periodic schedule, calling it ‘a mere drop in the bucket’ compared to the total budget for combating Delhi’s pollution. He also stated that IIT-Kanpur received approval for further trials this season, supported by Delhi Environment Minister Manjinder Singh Sira.
Public estimates indicate that the CAIPEX experiment (2017-2019) involved 103 flights, each priced at ₹15 lakh, totaling approximately ₹15 crore. The initial setup cost for infrastructure like radar and rain gauges was ₹33 crore, plus an annual maintenance fee of ₹5 crore. For commercial operations, a typical four-hour seeding mission would cost around ₹60 lakh.
Flight expenses represent a key variable. IITM previously noted that owning their aircraft could halve these costs. Dr. Agrawal highlighted that IIT-Kanpur possessed its own plane, which he deemed ‘a significant advantage.’
He emphasized the lack of existing data on winter cloud seeding in Delhi, stating, ‘We are establishing a baseline.’ While data analysis is ongoing, initial findings indicate a minor improvement in air quality in parts of Delhi NCR. He noted the absence of wind on the trial day, adding, ‘It’s a small step, but it’s a start. We’re not reinventing the wheel; we’re building it from scratch in this context.’
The CAIPEX experiments also included a separate study on ‘glaciogenic’ or ‘cold clouds’ (containing both ice and water), comparing 31 seeded clouds with 31 unseeded ones in Solapur. Both cloud types produced rain, but not directly at the seeding location. Their report concluded that ‘glaciogenic cloud seeding redistributed rainfall over a broader region, showing no discernible effect on rainfall at the specific CAIPEX experimental site.’
Dr. Agrawal was unsure if the IIT-Kanpur experiment specifically targeted cold clouds, noting that silver iodide, a potentially toxic substance, has historically been used in cloud seeding to generate snow. However, the IIT’s Cessna planes are limited to altitudes below three kilometers, making it unlikely they could reach the higher-altitude cold clouds that typically require top-down seeding.
Mr. Philip clarified via text message that the seeding mixture contained both nano-particle silver iodide (primarily glaciogenic material) and micro-sized rock/sea salt (hygroscopic material). He stated, ‘We dispersed the mixture using flares at the base of the clouds (warm clouds), indicating a hygroscopic seeding mechanism.’
The Earth Sciences Ministry scientist further elaborated on the complexity of cloud experiments: ‘The main challenge lies in precisely determining the optimal amount of salt mixture needed to form and grow water crystals. This demands extensive ground studies in cloud chambers, as both excessive and insufficient seeding can be counterproductive.’
The article also included a video from IIT-Kanpur, showing a Cessna 206H plane conducting cloud seeding over Delhi to combat air pollution on October 28, 2025.