Cloud seeding can’t be reliable strategy to tackle pollution in Delhi, says IIT study

The report, prepared this month at the Centre for Atmospheric Sciences (CAS) IIT Delhi, is the outcome of a “comprehensive analysis integrating climatological data (2011-2021), aerosol-cloud interaction assessments, and pollutant washout/recovery”.

The Delhi government conducted two back-to-back cloud seeding trials on October 28, in which a team from IIT-Kanpur flew a small aircraft over parts of Delhi and released silver iodide and salt particles in flares.

The idea was to induce artificial rain, and thus reduce air pollution above the capital. Rain is believed to reduce air pollution because it acts as a natural cleansing mechanism, washing soluble gases out of the atmosphere and depositing particulate matter on the ground.

A report released by the office of Delhi Environment Minister Manjinder Singh Sirsa after the trial said that as per data available on the ‘Windy’ website, two precipitation events were noted – 0.1 mm of rain fell in Noida at 4 pm, followed by 0.2 mm in Greater Noida. No rainfall was recorded in Delhi.

“There is a fundamental lack of sufficient moisture and saturation during the peak pollution months (December-January), coinciding precisely when intervention is most needed,” the IIT-Delhi report, titled ‘Can Cloud Seeding Help Tackle Delhi’s Air Pollution?’ says.

“While Western Disturbances (WDs) are the primary drivers of potential seeding conditions, viable “windows of opportunity” are rare, confined to specific anomalous events,” the report says.

“Even on days identified as potentially promising (e.g., cloudy WD days without rain), a multi-criteria Moisture Suitability Index (MSI) indicates they frequently lack the necessary combination of moisture depth, saturation, and atmospheric lift required for successful seeding,” it says.

The analysis confirmed that heavy natural rainfall is indeed highly effective in washing out PM2.5, PM10, and NOX, while “light rain offers minimal impact”. It noted, however, that “even after significant washout, air quality improvements are short-lived, with pollutant concentrations typically recovering to pre-event levels within 1-5 days due to persistent emissions”.

Also, “ozone concentrations often increase post-rainfall”, the study says. And “significant concerns remain regarding the environmental/ health impacts of seeding agents like AgI (silver iodide), high operational costs, and scientific uncertainties”.

The study underlines that a sustained reduction of emissions from diverse sources including vehicular traffic, industrial activities, construction dust, agricultural biomass burning, and residential heating, “remains the most viable and necessary long-term solution” to air pollution.

In 2024, after the then Delhi government asked the Centre about cloud seeding as an emergency measure to improve winter air quality in Delhi, “expert opinion was sought from the India Meteorological Department (IMD), Commission for Air Quality Management in NCR and Adjoining areas (CAQM) and Central Pollution Control Board (CPCB) regarding feasibility of cloud seeding for artificial rainfall in the Delhi during winter”, the government told Parliament in December 2024.

The experts opined that “effective cloud seeding requires specific cloud conditions, which are generally absent during Delhi’s cold and dry winter months”, the government told Parliament.

One of the mentors of the IIT-Delhi study, aerosol scientist Shahzad Gani, told The Indian Express on Friday, “The study looked at past data that showed that during the polluted winters of Delhi, atmospheric conditions are just not suitable for cloud seeding. Even when it rains, pollution comes back in a few hours or maximum in a day or two.”

“Solutions like cloud seeding and smog towers are a distraction and a waste of resources,” he added.