Opinion From the Opinions Editor | Can artificial rain quell Delhi’s pollution? Experiments in capital must be backed by science

The monsoon has withdrawn from most parts of the country and there are indications of an early onset of winter over the National Capital Region. The prospect of a long cold season has triggered fears of a smoky sky over the capital. The haze usually makes its appearance in the run-up to Diwali, and continues well past the winter. The Delhi government this time has a new weapon in its armoury against pollution – it is slated to trial cloud-seeding in early October to trigger artificial rainfall. The procedure that aims to check pollution from aggravation will involve aircraft flying beneath cloud layers and dispersing silver iodide. This compound interacts with water droplets in clouds, making them heavier so they condense and fall as rain.

According to an analysis by the Centre for Science and Environment Delhi was the country’s most polluted megacity by a wide margin during the 2024-25 winter, with an average PM2.5 concentration of 175 micrograms per cubic metre, according to an analysis by the Centre for Science and Environment. The Aam Aadmi party which was in office then had asked the Centre’s permission to trigger artificial rain, but it was stonewalled. Now when the BJP runs a “double engine sarkar” in Delhi, the Centre’s approval of the Rekha Gupta government’s cloud seeding plans has invited accusations of step-motherly behaviour. However, beyond the AAP-BJP politics, policymakers need to subject the technology to a critical analysis, take stock of its scientific complexities, before looking at artificial rain as a silver bullet for Delhi’s pollution problems.

In 1947, a tropical hurricane that was moving west to east in the US was pricked. The hurricane moved west, instead and made landfall at Savannah, Georgia. This was blamed on the experiment, and seeding hurricanes was abandoned for more than a decade. The US army used weather modification from 1967 to 1972 during the Vietnam War to extend the monsoon season, especially over the Ho Chinh Minh trail, that was a conduit of soldiers and supplies between the northern and southern parts of the Southeast Asian country. The resulting floods led to an international treaty, in 1977, against the used of weather warfare.

China has experimented with the technology since the 1960s to bring rain to the areas in the north of the country. Then, having chosen the monsoon months to conduct the Beijing Olympics of 2008, the Chinese government asked the city’s weather engineers to shoot and spray silver iodide and dry ice into incoming clouds, still far away, to flush out rain before it could reach the sporting centres. In recent years, Russia has used cloud seeding against forest fires in Siberia – drawing from an experiment in the 1980s to prevent radioactive rain from Chernobyl to reach Moscow.

That said, the jury on weather modification is still out. Scientist believe that the results of cloud seeding are difficult to quantify. Seeding can only change certain clouds and in 2021, the Central Pollution Control Board had said that the feasibility of the technology as an emergency measure to battle winter pollution in northern India will be limited, reasoning that insufficient moisture could reduce the method’s efficacy.

Delhi’s winters are typically dry with minimal cloud cover and data shows that over the past five years, during peak pollution episodes in Delhi and the surrounding areas, clouds are rarely present. The scale of the capital’s pollution problem is vast, and it requires continuous and intense rainfall over a large area to have a measurable impact. Rain triggered by cloud seeding can, at most, temporarily wash away pollutants but it does not address the source of particulate matter and pollution levels could rebound in a short time. That’s why the effects of weather modification on dust suppression in other parts of the world have, by and large, been episodic. The Delhi government must also heed the environmental red flags on cloud seeding that have been raised in several parts of the world.

In the coming weeks as the Delhi government experiments with weather modification to resolve the city’s long standing problem, it must strictly go by science.

Till next time

Kaushik