Why in news?

Amid worsening air quality, the Delhi government, in collaboration with IIT-Kanpur, conducted two cloud-seeding trials to induce artificial rain, though only negligible rainfall was recorded — 0.1 mm in Noida and 0.2 mm in Greater Noida.

According to experts, the weak results were due to low cloud moisture (15–20% humidity), but more sorties are planned as better moisture conditions are expected in coming days.

What’s in Today’s Article?

• Cloud Seeding
• Why Cloud-Seeding Trials in Delhi Failed to Induce Rain?
• How Cloud Seeding Helped Reduce Pollution?
• Conclusion

Cloud Seeding

• It is a weather modification technique used to enhance rainfall by introducing “seed” particles into suitable clouds.
  • The method was first tested globally in the 1940s.
• The process involves dispersing cloud condensation nuclei (CCN) — particles that attract water vapour — or ice nuclei particles, which promote ice crystal formation.
• In natural conditions, water vapour condenses around airborne particles to form droplets that grow, collide, and eventually fall as rain.
• In cloud seeding, artificial nuclei such as silver iodide or salt particles are added to accelerate this process.
• Ice crystals grow faster, combine, and become heavy enough to precipitate, increasing the likelihood of rainfall.
• Process of Cloud Seeding
  • To artificially induce rain, salts such as silver iodide, potassium iodide, or sodium chloride are used as “seeds” to create additional nuclei for cloud droplet formation.
  • These particles are dispersed into clouds using aircraft, ground-based generators, rockets, drones, or flares.
    • The method chosen depends on cloud type and conditions.
• Conditions Needed for Successful Cloud Seeding
• Cloud seeding can only be done when suitable clouds with adequate depth and moisture are present.
  • As per the experts, cloud seeding needs humidity above 50%, cool temperatures, and existing cloud formation.
• The process requires a sufficient number of droplets inside clouds to enlarge through condensation and eventually fall as rain. It cannot be done under clear skies.
• In Delhi’s winters, cloud formation depends on western disturbances — weather systems originating from the Caspian or Mediterranean Sea that bring non-monsoonal rain to northwest India.
• However, these clouds often lack the required depth and liquid water content for effective seeding.
• Experts emphasize that before any attempt, it’s essential to assess cloud height, moisture levels, and liquid water content using specialized monitoring tools to determine if conditions are right for seeding.
• Environmental concerns
  • Silver iodide (AgI), used in seeding, is insoluble but toxic in large quantities.
  • Even small amounts (0.2 micrograms) can harm fish and microorganisms, though iodine in AgI is not considered toxic.

Why Cloud-Seeding Trials in Delhi Failed to Induce Rain?

• A Delhi government report cited low atmospheric moisture (10–15%), as predicted by the India Meteorological Department (IMD), as the main reason the cloud-seeding trials did not produce significant rainfall.
• Experts explained that although there was good cloud cover, moisture levels were too low to trigger rain.
• They added that the team gained technical experience from the trials and would conduct a third round once weather conditions improve.
• Limited Rainfall and Technical Challenges
  • Experts noted that while Delhi plans more trials, cloud seeding in convective, low-level clouds remains highly uncertain.
  • Success depends on timing, cloud type, altitude, and adequate moisture, conditions that are rarely met over the plains.
    • Cloud bases were around 10,000 feet, which meteorologists said was too high for effective seeding.
    • If clouds descend below 5,000 feet, chances of rainfall improve.
  • The World Meteorological Organization (WMO) notes that the biggest challenge is quantifying seeding’s actual impact on precipitation.

How Cloud Seeding Helped Reduce Pollution?

• Despite limited rainfall — 0.1 mm in Noida and 0.2 mm in Greater Noida — the trials had a measurable impact on air quality.
• According to the Delhi government’s report, levels of particulate matter (PM2.5 and PM10) dropped after cloud seeding:
  • PM2.5 fell from 221–230 to 203–207 across Mayur Vihar, Karol Bagh, and Burari.
  • PM10 reduced from 206–209 to 163–177 in the same areas.
• The report concluded that while rainfall was minimal, pollution reduction was evident, offering valuable insights for future cloud-seeding efforts.
• Air Quality and Broader Solutions
  • Air quality analysts cautioned that cloud seeding does not address emissions at their source.
  • Experts point out that such measures — like smog towers or anti-smog guns — offer only short-term benefits.
  • Sustainable improvement requires coordinated action across states, targeting emissions from transport, power plants, and construction, under an airshed-based approach.

Conclusion

Delhi’s cloud-seeding trials provided valuable learning but limited rain, highlighting the complex science, environmental risks, and logistical constraints of such interventions.

Experts agree that while cloud seeding can supplement pollution control efforts, lasting air quality improvement demands systemic emission reductions and regional cooperation.