Cloud seeding: Process, Applications & Limitations

Context (TH): The Directorate General of Civil Aviation has approved cloud seeding trials to address air pollution in Delhi.

About Cloud Seeding

Cloud seeding is a weather modification technology that artificially stimulates rainfall by spraying chemical substances into the air that serve as cloud condensation nuclei.

Cloud condensation nuclei are small particles upon which water vapour condenses to form clouds.
The chemical substances used are silver iodides, potassium iodides, dry ice (solid carbon dioxide) or liquid propane.
It works only when there are enough pre-existing clouds in the atmosphere.
Weather Suitability: It requires tall, moist clouds and low wind conditions to operate effectively.
Pollution Removal: Artificial rain reduces particulate matter by washing pollutants out of the air.

Particulate Matter: Tiny solid or liquid particles (like dust, soot, smoke) that harm lungs and trigger respiratory and heart issues.

Hygroscopic Cloud Seeding: Salts are sprayed through explosives in the lower portions of clouds.
Static Cloud Seeding: Chemicals like silver iodide crystals are sprayed into clouds.
Dynamic Cloud Seeding: Vertical air currents are boosted to encourage more water to pass through the clouds which translates into more rain.

In the Solapur experiment, hygroscopic cloud seeding was used and calcium chloride flare was used for seeding the clouds.

Increases rainfall: In drought-prone or arid regions, cloud seeding can increase rainfall, helping farmers and ensuring food security.
Geoengineering Research: Cloud seeding is being explored in some climate engineering projects to counteract localized warming or extreme weather conditions.
Regulates weather: Creates favourable microclimates by dispersing fog, suppressing hail, and modifying cyclones.
Pollution Removal: Artificial rain reduces particulate matter by washing pollutants out of the air.
Airport Operations: In aviation, cloud seeding is used to dissipate fog (especially supercooled fog) near airports, improving visibility and flight safety.

Particulate Matter: Tiny solid or liquid particles (like dust, soot, smoke) that harm lungs and trigger respiratory and heart issues.

Cannot mitigate drought: It can simply partially address the water requirements.
Not All Clouds Are Suitable: Cannot produce rainfall from all clouds.
Moisture is essential: Requires the presence of moisture-bearing clouds.
Cause abnormal weather conditions: For e.g., when naturally less moisture place receives more rainfall, then it may cause flash floods.
Harmful for environment and health: Chemicals used in cloud seeding are toxic.
Contribute to global warming: The chemicals used in cloud seeding are a source of GHGs.

Delhi records alarmingly high pollution levels each year; in early 2025, it was ranked as India’s second most polluted city.
Delhi records alarmingly high pollution levels each year and was ranked India’s 2^nd most polluted city in early 2025, as per a mid-year assessment by the Centre for Research on Energy and Clean Air (CREA).

Vehicle Emissions: Diesel-heavy transport makes up about 40% of winter PM2.5 in Delhi.
Industrial Output: NCR Industries emits sulphur dioxide, nitrogen oxides, and fine particulate matter.
Construction Dust: Ongoing construction and demolition increase PM10 and coarse dust levels.
Waste Burning: Burning plastic and garbage worsens local air quality in many areas.
Stubble Burning: Crop residue fires in neighbouring states increase pollution in late autumn.
Weather Inversion: Winter inversions trap pollutants close to the ground, reducing dispersion.

Winter Inversions: A weather condition where warm air overlays cooler air near the surface, preventing vertical air movement and trapping pollutants close to the ground.