Introduction
Cloud seeding uses nucleating particles to enhance rainfall from existing clouds. Delhi’s failed 2025 trials exposed the limits of weather modification against winter air pollution without adequate cloud moisture and depth.
Microphysical Working Mechanism & Pollutant Scavenging
- Glaciogenic Seeding (Cold Clouds): Silver iodide crystals mimic ice structures, triggering rapid ice nucleation in supercooled liquid water clouds below 0 degree-celcious. Example: cIce crystal growth.
- Hygroscopic Seeding (Warm Clouds): Salt flares dispersed near the cloud base absorb ambient water vapor, accelerating droplet collision and coalescence. Example: Droplet coalescence expansion.
- Delivery Technology: Aircraft-mounted flares, ground generators, rockets and drones disperse seeding agents at suitable cloud levels. Example: Aerial dispersal.
- Wet Deposition & Aerosol Coagulation: Falling raindrops capture suspended , , and soot aerosols via physical coagulation, washing pollutants down to the surface Example: Wet aerosol scavenging.
Historical Evolution & Indian Experiments (CAIPEEX & Delhi Trials)
- Early Indian Trials (1950s–1980s): India initiated ground-based salt seeding experiments in 1951 (Tatas/IMD), followed by sustained warm-cloud seeding studies over Baramati, Maharashtra (1973–1986). Example: Baramati IITM trials.
- CAIPEEX Campaign (2009–2019): Conducted by the Indian Institute of Tropical Meteorology (IITM) under the Ministry of Earth Sciences over rain-shadow Solapur, CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement Experiment) demonstrated an average 18% relative rainfall enhancement in seeded convective clouds.
- Recent Delhi Pollution Trials (2025–2026): Conducted by the Delhi Government and IIT Kanpur using flare-equipped aircraft, the trials showed localized reductions in particulate matter near targeted corridors, though dry winter atmospheric conditions prevented significant city-wide rainfall.
Meteorological Limitations & Operational Constraints
- Pre-Existing Cloud & Moisture Dependency: Cloud seeding cannot generate clouds out of dry air; it requires deep convective clouds with sufficient liquid water content. Example: Winter moisture deficit.
- Temperature Inversion & Wind Shear: Winter temperature inversions over the Indo-Gangetic Plain trap pollutants near the surface while inhibiting vertical cloud development. Example: Atmospheric inversion layer.
- Overseeding & Ecological Risks: Excessive dispersion of nucleating particles can freeze droplets prematurely without precipitation, while accumulated silver iodide poses potential soil and aquatic toxicity. Example: Silver iodide accumulation.
Way Forward
- Prioritize Source-Level Emission Controls: Treat cloud seeding strictly as a temporary emergency tool under GRAP (Graded Response Action Plan) rather than a substitute for curbing vehicular, industrial, and stubble emissions.
- Integrate CAIPEEX Protocols under Mission Mausam: Leverage IITM’s randomized seeding protocols, Doppler radars, and cloud chambers under Mission Mausam to optimize operational timing and altitude.
- Mandate Environmental Impact Assessments: Establish continuous ecological monitoring of soil and groundwater to evaluate long-term chemical residues from repeated seeding operations.
- Mission Mausam: Use its ₹1,342.29-crore 2026–27 allocation to strengthen observation, modelling and forecasting not presume it funds cloud-seeding deployment.
Conclusion
As demonstrated by IITM’s CAIPEEX findings, cloud seeding is scientifically viable for enhancing rainfall in moisture-rich rain-shadow regions, yet remains constrained by dry winter meteorology in urban airsheds. Combining targeted weather-modification research with systemic emission reductions will secure sustainable environmental resilience.
