On October 28, despite clear warnings from the India Meteorological Department (IMD) that Delhi’s clouds wouldn’t be suitable for artificial rain, scientists from the Indian Institute of Technology Kanpur pressed ahead with their cloud-seeding experiment. They deployed a Cessna plane, releasing 10 kg of a silver iodide, common salt, and rock salt mixture into the sky—twice. Both attempts, aimed at inducing rain, were unsuccessful.
This particular Tuesday, marked by predictably ‘poor’ air quality in Delhi, represented a significant moment: the capital’s first cloud-seeding trial since 1972, and its inaugural attempt specifically targeting air quality improvement.
A senior scientist from the Ministry of Earth Science (MoES) informed The Hindu that while cloud condition data was shared with IIT-Kanpur, no specific advice was given on proceeding with the seeding. The MoES official explained that the Indian Institute of Tropical Meteorology (IITM), Pune, has extensively researched cloud seeding with inconclusive results regarding its reliability. Therefore, their input was merely to confirm that ‘there were no clouds’ suitable for the operation.
M. Mohapatra, Director-General of IMD, corroborated that cloud data was indeed ‘shared,’ but stressed its generic nature, stating, ‘The information on clouding and humidity is available to anyone.’
Manindra Agrawal, Director of IIT-Kanpur and the leading figure of the institute’s program, acknowledged prior consultations with IITM and IMD, noting their ‘negative’ feedback and skepticism about cloud seeding’s effectiveness for winter pollution. Despite this, IIT-Kanpur, a prominent institution with significant scientific influence and involvement in numerous Central and Delhi State projects, including those related to air quality, proceeded with the trial.
Mr. Agrawal defended the initiative to The Hindu, asserting, ‘But it does work,’ citing successful applications in China and the UAE, even if results in India have been mixed. He clarified that proceeding with the trial despite IMD’s unfavorable cloud forecast was a conscious decision to evaluate their ‘proprietary solution’—a blend of 20% silver iodide, rock salt, and common salt, with flares produced in Sivakasi, Tamil Nadu. Agrawal acknowledged the cloud moisture content was below the 15% threshold typically required for effective seeding but emphasized the need to gather data on their domestically developed salt mixture’s potency.
For decades, cloud seeding—the process of dispersing chemical aerosols into rain-bearing clouds to stimulate precipitation—has been a research focus in India. The Indian Institute of Tropical Meteorology (IITM), Pune, a leading authority, has been meticulously studying its potential to enhance monsoon rainfall since 2009.
Indian State governments have previously engaged private firms for cloud seeding during droughts, but outcomes have been inconsistent. This is because the technology cannot create clouds; it can only augment existing ‘warm clouds’ that contain minimal water vapor.
This raises a critical question: if clouds already possess enough water vapor to rain naturally, what actual benefit does seeding provide?
The IITM-CAIPEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) was specifically designed to address this question. Emulating randomized clinical trials in medicine, CAIPEX researchers conducted an experiment over Solapur, Maharashtra—a drought-prone area. They identified 276 ‘warm clouds,’ treating 151 of them by releasing chemical powder from flares attached to aircraft wings, while leaving the remaining 125 unseeded to serve as a control group.
Conducted during the 2018 and 2019 monsoon seasons, the clouds were selected using radar for characteristics and rain gauges for rainfall measurement. This data guided the deployment of aircraft, with each sortie costing ₹15 lakh, to target specific clouds. The findings revealed that half of the seeded clouds and nearly 70% of unseeded clouds dissipated without producing rain. However, approximately 40% of seeded clouds resulted in rainfall, compared to 27% of unseeded clouds.
Significantly, seeded clouds produced an average of 46% more rain at the treated locations than their unseeded counterparts. Downwind, over a 100 sq. km. area, seeded clouds delivered an 18% increase in rainfall, confirmed by chemical analysis of water collected by rain gauges, distinguishing between seeded and natural precipitation.
The key takeaway from CAIPEX was that warm-cloud seeding is effective solely for enhancing monsoon rainfall, provided specific conditions are met. These include careful selection of appropriate clouds, using only calcium chloride at the cloud base, employing radar and gauge systems, and targeting specific cloud types. Comprehensive results and an FAQ are publicly accessible on the IITM website.
Given Delhi government’s track record of deploying urgent solutions—from smog towers to odd-even car schemes—cloud seeding as a smog-clearing strategy has been considered for at least seven years. However, unlike the monsoon-focused CAIPEX experiments, this application would occur outside the monsoon season, a period when the crucial ‘warm clouds’ are typically scarce.
For at least seven years, the Central government has consistently rejected Delhi’s cloud-seeding proposals. The scientific community, including IITM and IMD, maintains a unified stance, as articulated by Union Minister of State for Environment Kirti Vardhan Singh in December 2024: ‘Effective cloud seeding demands specific cloud conditions, which are generally absent during Delhi’s cold and dry winter months. Even if ideal clouds materialized, precipitation might evaporate in the dry lower atmosphere before reaching the ground. Furthermore, uncertainties, efficacy issues, and potential adverse effects of seeding chemicals persist.’
Mr. Agrawal acknowledges that post-monsoon and winter months (October-February) typically lack moisture-rich clouds conducive to air-clearing rainfall. However, he argues the endeavor is not futile. ‘IMD data indicates 4-5 Western Disturbances—rain-bearing storms from the Mediterranean—occur during this season, carrying moist clouds. If we seed once every 10 days and reduce the Air Quality Index significantly for three days, that’s a 30% reduction in pollution impact. That’s a win,’ he asserted.
When questioned about the necessity of seeding if Western Disturbances naturally alleviate pollution, Mr. Agrawal responded that ‘seeding would only enhance rain, and the more rain, the better.’ He deems the experiment worthwhile, estimating winter cloud seeding over Delhi would cost ₹30 crore under his proposed schedule. ‘That is a drop in the bucket for the overall budget to reduce Delhi pollution,’ he commented, adding that IIT-Kanpur received ‘encouragement’ for further trials this season from Delhi Environment Minister Manjinder Singh Sira.
Public estimates show the 2017-2019 CAIPEX experiment involved 103 flights, costing ₹15 lakh each, totaling approximately ₹15 crore. The initial infrastructure setup (radar, rain gauges, radiosondes) was ₹33 crore, with annual maintenance at ₹5 crore. Commercial seeding operations typically average four hours and cost around ₹60 lakh per operation.
Flying costs are a major variable. IITM previously noted that owning its aircraft could halve expenses. Dr. Agrawal highlighted IIT-Kanpur’s advantage of having its own plane available for trials.
Agrawal emphasized, ‘There is zero data on cloud seeding in Delhi during winter, and we are establishing a baseline.’ He noted that while data analysis is ongoing, preliminary reports indicate a ‘slight improvement in air quality’ in parts of Delhi NCR, despite zero wind that day. ‘It is very little but definitely something. We are not reinventing the wheel; it doesn’t exist,’ he added.
CAIPEX also included a component on ‘glaciogenic’ or ‘cold clouds’ (containing both ice and water), seeding 31 such clouds in Solapur and comparing them with 31 unseeded ones. Both types produced rain, though not at the seeding location. Their report stated, ‘Glaciogenic cloud seeding redistributed rainfall over a wider area, and had a non-discernible impact on rainfall at the CAIPEX experimental location.’
Dr. Agrawal was unsure if IIT-Kanpur’s experiment targeted cold clouds. Historically, silver iodide, a potentially toxic substance used in their mixture, has been employed for glaciogenic seeding to create snow. However, the IIT’s Cessna planes have an altitude limit of three kilometers, making it unlikely they could reach and seed cold clouds, which are typically higher and require top-down application.
Mr. Philip clarified via text message: ‘The seeding mixture contains both nano-particle silver iodide (primarily glaciogenic) and micro-sized rock/sea salt (hygroscopic). We dispersed it 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: ‘The challenge in cloud experiments lies in precisely determining the optimal amount of salt mixture needed to create water crystals that can grow. This necessitates extensive ground studies using cloud chambers, as both excessive and insufficient seeding can be counterproductive.’