SYLLABUS

GS-3: Environmental pollution and degradation; Science and Technology- Developments and their Applications and Effects in Everyday Life.  

Context: 

According to an IIT Delhi report, cloud seeding cannot be a primary or reliable strategy for Delhi's winter air pollution management, as Delhi’s winter atmosphere is climatologically unsuitable for consistent cloud seeding. 

More on the News

• The report, titled “Can Cloud Seeding Help Tackle Delhi’s Air Pollution?”, analysed climatological and air quality data from 2011 to 2021. 
• It also assessed cloud moisture, aerosol-cloud interactions and the ability of rainfall to wash out pollutants such as PM2.5, PM10 and nitrogen oxides.
• The report comes against the backdrop of the Delhi government conducting two cloud-seeding trials in Burari, north Karol Bagh and Mayur Vihar in collaboration with IIT Kanpur, but there was no rain. 

Key Findings of the Report 

Unfavourable Winter Conditions: Winter temperature inversions and stagnant, dry air hinder cloud formation, making effective seeding difficult.

Temporary Pollution Relief: 

• Even when seeding triggers light rain, any reduction in pollutants lasts only 1–3 days before emissions push levels back up.
• It found that heavy rain can remove more than 80%of particulate matter and nitrogen oxides from the air, while light rain has little impact.

Moisture Suitability Index (MSI): The study’s MSI indicate that the necessary combination of moisture depth, saturation, and vertical uplift required for successful cloud seeding occurs rarely and only during sporadic events such as western disturbances.

Limited Measurable Impact: The report concludes that cloud seeding should be considered, if at all, only as a costly, emergency short-term measure under stringent forecasting conditions, not as a regular pollution control strategy.

Implementation challenges

• Environmental and Health Concerns: Critics point out that repeated or large-scale use of silver iodide may lead to cumulative accumulation in soil, water or crops, and possibly affect human health or ecosystems.
• Narrow Weather Windows: The 10-year analysis data found only about 90–100 days with moisture and cloud conditions comparable to natural moderate-to-heavy rainfall, thus making seeding operations highly challenging.
• Cost-effectiveness and scalability: The cost of seeding sorties, together with dependency on highly favourable conditions, raises questions about whether this is a cost-effective strategy for routine pollution management in a large urban area. 
• Unintended weather/eco-impacts: Weather modification may carry risks of altering local precipitation patterns, affecting neighbouring regions, or impacting ecosystems in subtle ways. 

Policy Recommendations 

• Limit Cloud Seeding to a Supportive Role: Cloud seeding should not be treated as a primary or independent solution for Delhi’s air pollution and must be considered only as a supplementary, situational measure.
• Prioritize Long-term Emission Reductions: Durable air-quality improvements depend on sustained emission control across transport, industry, construction, and biomass burning sectors.
• Strengthen Research and Innovation: Further research is needed to refine seeding timing and chemical formulations, while also exploring alternative technological interventions for pollution mitigation.
• Set clear criteria and thresholds for deployment: Define meteorological, cloud-moisture and aerosol conditions under which seeding may be attempted, and establish cost-benefit thresholds to decide when not to proceed. 

About Cloud Seeding 

Cloud seeding, as defined by the Indian Institute of Tropical Meteorology (IITM), is a weather modification technique that uses "seed" particles to modify suitable clouds to increase rainfall. 

Cloud seeding includes multiple types:

• Glaciogenic seeding (using ice nuclei like silver iodide, dry ice (solid CO2) in cold clouds with supercooled water).
• Hygroscopic seeding (using salts such as sodium chloride in warm clouds to enhance droplet coalescence).
• Dynamic seeding (aimed at boosting vertical air currents to enhance cloud formation).

Mechanism: 

• The process works by dispersing seed particles called Cloud condensation nuclei (CCN), often silver iodide, through flights into moisture-containing clouds to provide surfaces around which water vapour can condense.
• These particles have a molecular structure similar to ice crystals, which encourages supercooled water droplets in the cloud to freeze and form ice crystals.
• As ice crystals grow larger by collecting moisture, they eventually become heavy enough to fall as precipitation, rain or snow, thereby increasing natural rainfall.

Sources:
Indian Express
The Print
Hindustan Times