Delhi’s winter atmosphere unsuitable for cloud seeding: IIT Delhi report

According to the IIT Delhi report, Delhi’s winter atmosphere is climatologically unsuitable for consistent cloud cultivation due to fundamental lack of adequate moisture and saturation, especially in the months of December and January when pollution is at its highest.

The report, based on a comprehensive analysis by IIT’s Center for Atmospheric Sciences integrating climatological data (2011-2021), comes against a backdrop where the Delhi government in collaboration with IIT Kanpur has conducted two cloud seeding trials in Burari, north Karol Bagh and Mayur Vihar, but no rainfall. The institute had previously conducted successful trials in Kanpur in 2017-18, but this was the first such trial in the National Capital Region (NCR) region of Delhi.

“While cloud seeding is theoretically possible under certain atmospheric conditions, during Delhi’s winter, its practical utility as a consistent and reliable intervention in air quality is limited. The required atmospheric conditions are rare and often overlap with natural precipitation, limiting potential marginal gains,” the report said. he said.

“Even if successful, induced rainfalls will likely provide only a short period (usually one to three days) before pollution levels rise again. Given the high operating costs, scientific uncertainties inherent in aerosol-laden environments, and the lack of any impact on underlying emission sources, cloud seeding cannot be recommended as a primary or strategic measure for Delhi’s pollution management.”

“At best, it can serve as a high-cost, tactical intervention during declared air quality emergencies, subject to a forecast meeting stringent MSI-based eligibility criteria. Ultimately, the study underscores that sustained emissions reductions remain the most appropriate and durable solution to Delhi’s chronic air pollution crisis,” he added.

The report stated that the ten-year analysis (2011-2021) showed that the key winter months of December and January coincide with both the most severe pollution periods and the driest climatic conditions.

“There is a fundamental lack of adequate moisture and saturation during the peak pollution months (December-January), precisely when intervention is most needed. While Western Disturbances (WDs) are major drivers of potential seeding conditions, viable ‘windows of opportunity’ are rare and limited to specific abnormal events.”

“Even on days identified as potentially promising (e.g., cloudy WD days with no rain), the multi-criteria Moisture Suitability Index (MSI) indicates that the combination of moisture depth, saturation, and atmospheric lift required for successful seeding is often missing,” he said.

The study highlights the complexities arising from Delhi’s high aerosol environment.

High aerosol loading [characterised by high Aerosol Optical Depth (AOD)] It is associated with increased cloud cover and higher liquid/ice water content, especially during wet conditions.

However, favorable microphysical conditions (low cloud base, high water content) often coincide with naturally occurring precipitation, limiting the potential additional benefit of seeding. The vertical separation between the shallow aerosol layer (below 2 km) and typical seedable cloud layers (2-5 km) also presents significant operational targeting challenges.

Thermally glacier-inducing seeding appears potentially viable in mid-winter, but operational feasibility appears limited by current wet conditions.

Regarding pollution removal, the analysis confirms that heavy natural rainfall is highly effective (80-95% removal for PM2.5, PM10, NOX), while light rain provides minimal impact. More importantly, even after significant cleanup, improvements in air quality are short-lived; pollutant concentrations typically return to pre-event levels within one to five days due to persistent emissions.

Ozone concentrations generally increase after rain. While dry WDs provide limited aeration, significant concerns remain regarding the environmental/health impacts, high operating costs, and scientific uncertainties of seeding agents such as AgI (silver iodide).

“Given these constraints, cloud seeding cannot be recommended as a primary or reliable strategy for Delhi’s winter air pollution management. At best, it should be viewed as a potentially high-cost, emergency short-term measure subject to strict forecasting criteria.”

“The study underlines that sustained emissions reductions remain the most feasible and necessary long-term solution,” the report said.

It was published – 01 November 2025 11:17 IST