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

An assessment by IIT Delhi’s Centre for Atmospheric Sciences concludes that the National Capital Region’s winter atmosphere is, in most years, too dry and poorly suited for dependable cloud seeding. The analysis, which synthesizes a decade of climatological data (2011–2021), finds that the combination of limited moisture, weak saturation, and insufficient atmospheric lift during December and January—the very months when air pollution peaks—undercuts the odds of meaningful, repeatable outcomes.

Why winter rarely cooperates

The report underscores a stark seasonal mismatch: the core winter months bring Delhi’s hardest-hitting smog episodes precisely when the atmosphere is at its driest. Western Disturbances occasionally create the kind of conditions that might allow seeding, but these “windows” are uncommon and often coincide with rainfall that would have occurred anyway.

Even on days that appear promising—such as cloudy Western Disturbance events without precipitation—the study’s Moisture Suitability Index (MSI), which accounts for moisture depth, saturation, and vertical motion, frequently flags shortfalls. Simply put, the atmospheric ingredients needed for seeding rarely align in Delhi’s winter, and when they do, nature often beats the planes to it.

Trials highlight the limits

Recent pilot efforts in parts of Delhi, including Burari, Karol Bagh, and Mayur Vihar, produced no rainfall, in contrast to earlier demonstrations over Kanpur in 2017–18 that reported success. The disparity illustrates how region-specific meteorology matters: Delhi’s winter boundary layer and moisture profiles differ significantly from locations where seeding has shown promise, limiting the technique’s reliability in the capital.

Aerosols complicate the picture

Delhi’s heavy aerosol load adds another layer of complexity. Elevated aerosol optical depth is often linked to enhanced cloudiness and greater liquid or ice water content, especially during rainy spells. Yet those favorable microphysical conditions tend to coincide with precipitation that would occur without intervention, blunting the added value of seeding.

Operationally, there is also a mismatch in altitude: the densest aerosol layer typically sits below about 2 kilometers, while the seedable cloud decks are more often found between 2 and 5 kilometers. This vertical separation complicates targeting, dosage, and timing. Thermodynamic analyses suggest that glaciogenic seeding could be thermally viable in mid-winter, but in practice, opportunities are mostly restricted to periods when it is already raining.

Rain’s brief reprieve for pollution

The study confirms that heavy natural rainfall can wash out between 80% and 95% of pollutants such as PM2.5, PM10, and NOx. Light showers, by contrast, do little to reduce concentrations. Even after a strong downpour, improvements are fleeting: with emissions continuing unabated from traffic, industry, solid fuel combustion, and construction dust, pollutant levels typically rebound to pre-rain conditions within one to five days. The analysis also notes that ozone often ticks upward after rainfall episodes as atmospheric chemistry shifts.

While dry Western Disturbances sometimes provide modest ventilation, the report flags several concerns around cloud seeding as an air-quality tool: substantial operational costs, scientific uncertainties in aerosol-rich environments, targeting challenges, and questions about the environmental and health implications of commonly used seeding agents such as silver iodide.

What the science says about strategy

According to the assessment, cloud seeding in Delhi’s winter cannot be relied upon as a primary pollution-control measure. At best, it could serve as a tactical, short-term option during declared air-quality emergencies—and only when forecasts meet strict, MSI-based suitability thresholds. Even then, any reprieve would likely last one to three days before pollution resurges.

The broader conclusion is unequivocal: durable improvement depends on cutting emissions at the source. That means persistent action across transport, industry, power, waste burning, and construction dust; stronger inspection and enforcement; expanded clean energy and electrified mobility; and better coordination of early warnings with rapid-response controls. In a climate where moisture is scarce precisely when relief is most needed, technological quick fixes offer limited returns. Winter-ready air, the report argues, must be earned through sustained, year-round emission reductions.