‘Gains short-lived… programmes can cost up to Rs 3 crore’: Experts on why cloud seeding may not work

Even as Delhi plans more such trials in the future, experts caution that evidence for seeding-led rain in convective, low-level clouds is uncertain, any air-quality gains are short-lived, and the timing, cloud type, and moisture must align almost perfectly.

These conditions, they said, often do not hold over the plains.

A World Meteorological Organisation review notes that a key challenge is reducing the uncertainty in quantifying the impact of seeding on precipitation.

With cloud bases around 10,000 feet on Monday, Skymet Weather meteorologist Mahesh Palawat said, “Cloud seeding is hard to achieve at this height. If the clouds come down by the evening and remain less than 5,000 feet in altitude… the situation can change.”

Air quality analysts have also stressed that seeding does not target emissions at the source.

“Addressing air quality requires tackling sector-specific emissions from transport, power, and construction. Without that, no real impact can be achieved,” said Sunil Dahiya, analyst and founder at Envirocatalysts.

He said cosmetic measures like smog towers, anti-smog guns, or cloud seeding may create short-term visible benefits but are not sustainable solutions. “The focus should instead be on coordinated action across states and agencies through an airshed-based approach that targets the actual sources of pollution,” Dahiya added.

Experts also said the timing of the exercise is also crucial.

In a 2023 report on cloud seeding, the Indian Institute of Tropical Meteorology noted: “One major aspect is that clouds grow rather rapidly and we need to target clouds in the early part of their growth before they start raining. The seeding in raining clouds will wash out seed particles into the boundary layer and will not serve the purpose. So, one needs to decide the correct time to intervene.”

It added that the pilot must understand seeding near the cloud base in updrafts and be proactive. Safety is critical because flying in upper-level clouds can lead to icing on the aircraft, which is hazardous. A coordinated team, accurate weather intelligence, awareness of severe weather, and bird-strike risk are required.

Dr Surendra K Dhaka, professor of Atmospheric Physics at Rajdhani College, also said the method needs “pre-existing cloud formation, relative humidity above 50%, and lower temperatures to hasten precipitation”.

He described Delhi’s aerosol mix as complex — with sulphates and silica dust — and not all of them are hygroscopic (tending to absorb moisture from the air). “Formation can take several hours and there is no certainty… Trials have been attempted in Tamil Nadu, Karnataka, China, the United States, and parts of Africa, sometimes for wildfires or drought relief,” said Dr Dhaka.

On the cost, he said programmes can run to about Rs 3.2 crore or more. “While several factors are beyond our control, if it works, the outcome could be immensely beneficial. It’s because conducting a cloud seeding experiment here will be crucial to understand the underlying science. Though such programmes are cost-intensive, their potential impact far outweighs the city’s pollution-related health expenditure.”

Meanwhile, environmental impact studies on cloud seeding are limited.

The IITM’s 2023 report, noted: “… AgI (silver iodide) is an insoluble substance used in cloud seeding. The soluble form is toxic in high amounts — say 10 gm of silver nitrate (which was used in early days) consumed by a human is fatal and the safety limits vary for different organisms.”

Stating that there is “insufficient evidence” on the environmental impact, it added, “But even small amounts (0.2 micrograms) are highly toxic to fish, microorganisms, etc. (aquatic life). Cloud seeding may increase 2-50 times of Ag (that is up to 20 micrograms noted from

observations). Iodine is 54% of the mass of AgI molecules and is not found to have toxicity levels.”

In its recommendation, any seeding programme should evaluate environmental impacts. Only a certain type of seeding in a certain cloud type (Glaciogenic seeding in orographic clouds) is strongly documented especially in the United States; there is no documented physical evidence of hygroscopic seeding in convective clouds, the IITM report noted.

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