Delhi Air Pollution: Why Cloud Seeding in Winter Has a Low Chance of Success
Table of Contents
Source: The Indian Express
Relevance: GS Paper–III: Science and Technology ,Environment and Ecology
Important Keywords:
For Prelims:
Cloud Seeding, Silver Iodide, Salt Mixture, CAIPEEX
For Mains:
Effectiveness of cloud seeding, India’s scientific experiments, CAIPEEX findings, limitations in post-monsoon atmosphere, and implications for air pollution control.
Why in News?
In November 2025, the Delhi government, with IIT Kanpur and IITM Pune, attempted cloud seeding to curb pollution. Experts warned of low success in winter due to unfavourable weather conditions.
Background
Every winter, Delhi’s air quality plunges to hazardous levels due to a mix of factors — crop residue burning, vehicular emissions, industrial pollutants, and unfavourable weather conditions. In search of quick fixes, authorities often turn to experimental technologies like cloud seeding or smog towers, despite limited scientific evidence supporting their long-term effectiveness.
What is Cloud Seeding?
Cloud seeding is a weather modification technique aimed at inducing artificial rainfall by dispersing certain substances into clouds, such as:
- Silver Iodide (AgI)
- Sodium Chloride (NaCl)
- Potassium Iodide (KI)
These substances act as condensation nuclei, around which water vapour condenses or ice crystals form, potentially resulting in rain.
However, the technique works only on specific types of clouds—particularly hygroscopic clouds (warm-rain clouds) that already contain adequate moisture.
History of Cloud Seeding
Global Developments:
- 1940s (U.S.): scientists William Schaefer and Bernard Vonnegut discovered that dry ice could induce ice crystal formation, causing snowfall over Pittsfield, Massachusetts. This led to Project Cirrus, an early but failed attempt to modify hurricanes.
- 1950s–60s: Cloud seeding spread globally — the Soviets used it to clear skies over Leningrad, the U.S. launched Project Skywater using silver iodide, and China used it to ensure clear skies during the 2008 Beijing Olympics.
India’s Experience:
- 1952 (Kolkata): First experiment by S.K. Banerji (IMD DG) using salt and silver iodide through hydrogen balloons.
- 1962 (Delhi): Attempted cloud seeding again, but it failed.
- 1970s onward: Moved to aircraft-based seeding using salt sprays, with research focusing on cloud microphysics, condensation, and rain-bearing cloud formation.
Delhi Trials 2025
- Conducted by: IIT Kanpur
- Objective: Induce rainfall to reduce smog and particulate matter.
Outcome:
- Two flights conducted; flares released into clouds.
- Only light drizzle reported in parts of Delhi.
- No significant rainfall recorded.
- Minor improvement in air quality observed.
Challenges:
- Poor cloud quality with low moisture content below 15%.
- Post-monsoon atmosphere not suitable for droplet formation.
- CAIPEEX had earlier shown only monsoon clouds yield measurable rain.
Next Steps:
- Despite limited success, IIT Kanpur plans to continue trials during the season.
Scientific Limitations of Cloud Seeding
Lack of Suitable Clouds in Winter:
- Hygroscopic clouds, necessary for seeding, mainly form during pre-monsoon and monsoon
- Between November and January, their occurrence over Delhi falls to 5–10%, compared to around 50% during monsoon months.
- Thus, winter conditions rarely support effective seeding.
Temperature and Aerosol Interactions:
- Light drizzles in cool weather can worsen pollution instead of reducing it.
- PM2.5 particles attach to micro-droplets, forming secondary aerosols, which lead to a rebound in pollution levels.
Short-Lived Benefits:
- Even when successful, rainfall effects are temporary.
- Pollutants quickly re-accumulate as emissions from vehicles, industries, and biomass continue.
The CAIPEEX Project
- Full Name: Cloud Aerosol Interaction and Precipitation Enhancement Experiment
- Initiated by: Indian Institute of Tropical Meteorology (IITM), Pune in 2009.
- Objective: Scientific assessment of cloud seeding’s impact on rainfall.
- Study Period: 2017–2019 over Solapur, Maharashtra, a drought-prone region.
- Method:
- Aircraft fired calcium chloride flares (no silver iodide) into selected clouds.
- Compared seeded and unseeded clouds using radar and ground data.
- Findings:
- 46% more rainfall in seeded clouds.
- 18% more rainfall downwind across a 100 sq. km area.
- Total enhancement: 867 million litres of extra water.
- Significance:
Provided quantifiable evidence that seeding can enhance rainfall under favourable monsoon conditions.
Policy Implications and the Way Forward
Strengthen Long-Term Mitigation:
- Transition from fossil fuels to renewable energy and electric mobility.
- Promote public transport and traffic decongestion strategies.
Year-Round Monitoring:
- Implement continuous source apportionment studies.
- Establish airshed-level emission inventories for better forecasting.
Scientific Validation:
- Any experimental technology like cloud seeding must undergo rigorous evaluation before large-scale deployment.
- Focus should shift from quick fixes to sustainable solutions.
Conclusion
Delhi’s cloud seeding trials reflect scientific curiosity but not sustainable problem-solving. Artificial rain offers short-term psychological relief rather than measurable environmental gains. Air pollution in Delhi is a systemic and regional issue, demanding coordinated action across states, backed by credible science, clean energy transition, and strong public awareness.Until emissions are controlled at the source, no amount of artificial rain can wash away Delhi’s toxic air.
UPSC PYQ
Artificial rainfall for pollution reduction uses: (IAS/2025)
(a) Silver nitrate and potassium iodide
(b) Silver iodide and potassium iodide
(c) Silver iodide and potassium nitrate
(d) Silver nitrate and potassium chloride
CARE MCQ
With reference to Cloud Seeding in India, consider the following statements:
- The first cloud seeding experiment in India was conducted by IMD in 1952.
- The CAIPEEX project recorded about 46% more rainfall in seeded clouds.
- The Delhi 2025 trials successfully induced widespread rainfall.
How many of the above statements are correct?
(a) Only one
(b) Only two
(c) All three
(d) None
Answer: (b) Only two
Explanation:
- Statement 1 – Correct: Conducted by IMD under S.K. Banerji in 1952.
- Statement 2 – Correct: CAIPEEX observed 46% more rainfall in seeded clouds.
- Statement 3 – Incorrect: Delhi trials produced only light drizzle, not widespread rainfall.