No rain, second cloud seeding trial on hold due to low moisture

The second phase of Delhi’s cloud seeding trial, scheduled for Wednesday, was called off by the IIT-Kanpur due to low moisture in the clouds. The institute said the process is “highly dependent on the right atmospheric conditions,” and the existing levels — around 15-20 per cent — were too low to conduct the operation.

“While rainfall could not be triggered yesterday because moisture levels were around 15 to 20 per cent, the trial delivered valuable insights,” the IIT-Kanpur said in an official statement.

According to the institute, data from monitoring stations across Delhi showed a “measurable reduction of 6 to 10 per cent in PM2.5 and PM10 concentrations,” suggesting that even under limited moisture conditions, cloud seeding could have some impact on air quality.

Environment Minister Manjinder Singh Sirsa said: “This is among India’s biggest scientific steps for urban air quality control.”

“Depending on the results, we are prepared for further cloud seeding sorties in the coming weeks. After the first round of trials, the results will determine whether we should plan more seeding experiments till February," he said.

However, several experts have questioned both the feasibility and scientific basis of conducting such experiments during Delhi’s dry winter months.

Chandra Bhushan, CEO of the International Forum for Environment, Sustainability & Technology (iFOREST), think tank working on environmental issues, said Delhi’s atmospheric conditions during winter are known to be unsuitable for artificial rain. “This is not new information. The Ministry of Environment had already told Parliament last year that Delhi’s winter conditions are not suitable for cloud seeding,” he said. “Cloud seeding works best as a drought management tool, not as a pollution control method,” Bhushan said.

Bhushan said “while experiments are part of scientific research, these must be conducted with scientific rigour and ethics, not for optics.”

Experts also pointed out that cloud seeding requires at least 50 per cent moisture in the clouds for effective results. Dr Shahzad Gani, Assistant Professor at the Centre for Atmospheric Sciences, IIT Delhi, said the failure was expected. “The point is not that it did not work — the point is that it cannot work,” he said. “During these months, Delhi’s air is extremely dry. Even if cloud seeding was possible, it cannot be used as a tool to address pollution,” he said.

Dr Gani also questioned IIT-Kanpur’s claim that the trial led to a “measurable reduction of 6 to 10 per cent” in PM2.5 and PM10 concentrations.

“Correlation is not causation. The decrease in particulate matter could simply be due to minor changes in wind speed or atmospheric conditions. It cannot be attributed to cloud seeding when it did not even rain,” he said.

Sunil Dahiya, lead analyst and founder of Envirocatalysts, a Delhi-based environmental think tank, called the exercise a “distraction from real solutions.” He said the trials “were a waste of money” and diverted attention from measures needed to reduce emissions at the source.

“None of the logic behind this experiment holds. The operation was conducted even when the required moisture conditions were not met. It cannot be considered a scientifically valid trial,” he said.

The data shared with the media after the trial on Tuesday said before the first seeding PM2.5 at Mayur Vihar, Karol Bagh and Burari was 221, 230, and 229 µg/m³, respectively, which fell to 207, 206, and 203 µg/m³, respectively, after the operation.

It also said PM10 at the same sites dropped from 207, 206, and 209 µg/m³ to 177, 163, and 177 µg/m³ post seeding.

Dr Anju Goel, Associate Director, Centre for Air Quality Research, The Energy and Resources Institute (TERI) said: “These numbers could be representative of AQI values for PM2.5 and PM10 concentrations and are wrongly written as PM2.5 and PM10 levels.”

She explained, for instance if Mayur Vihar had a PM2.5 AQI of 221 and a PM10 AQI of 207, that would make sense — but it should be reported as AQI, not µg/m³. When presented as pollutant concentrations (µg/m³), those numbers are misleading and technically wrong, since PM2.5 cannot exceed PM10.

The Tribune has reached out to the Delhi Government for clarification, but has not heard back till the time of publishing of this report.

Dahiya further pointed out that cloud seeding cannot serve as a practical solution for Delhi’s pollution problem. “You cannot keep flying aircraft over the city every time pollution spikes. Even if the experiment had been successful, it would have covered only a small area and a limited time frame,” he said.

The failed trial, experts said, underscores Delhi’s misplaced focus on quick fixes over lasting solutions. Dr Gani said, “We need to do the hard work of reducing sources and making the remaining ones cleaner. Everything else depends on favourable meteorology, which we cannot and should not try to control.”

With the second trial postponed indefinitely, the IIT-Kanpur said it would continue analysing the data from Tuesday’s experiment and refine its future operations. The institute maintained that the exercise provided “valuable insights” into how atmospheric interventions could influence air quality, even under suboptimal conditions.