Recently, the Delhi government, in collaboration with the Indian Institute of Technology (IIT) Kanpur, conducted cloud-seeding trials to induce rain as part of efforts to reduce the city’s air pollution.
About Cloud Seeding
- Definition: Cloud seeding is a weather modification technique that aims to enhance precipitation (rain or snow) by dispersing substances into the atmosphere that serve as cloud condensation or ice nuclei.
- Objective: To induce rainfall in moisture-bearing clouds or to augment natural precipitation processes.
Mechanism of Cloud Seeding
- Identification of Suitable Clouds: Only moisture-laden clouds with sufficient water vapour content are suitable.
- Typically, cumulus or stratiform clouds are targeted.
- The temperature, humidity, and wind conditions are analyzed before seeding.
- Seeding Agents Used: Chemicals used to trigger condensation or freezing include Silver iodide (AgI), Sodium chloride (NaCl), Potassium iodide (KI), Dry ice (solid CO₂)
- These materials act as condensation or ice nuclei — helping water vapour to condense into droplets or ice crystals.
- Method of Dispersal:
- Aerial Method: Chemicals are released from aircraft or drones directly into clouds; Most effective for large-scale cloud systems.
- Ground-based Method: Generators or rockets release seeding material from the ground; Winds carry the particles upward into the clouds.
- Microphysical Reactions in Clouds: Once the seeding material reaches the cloud,
- Water vapour condenses (if warm cloud seeding) or freezes (if cold cloud seeding) around the introduced particles.
- These droplets or ice crystals grow in size by colliding with nearby particles.
- Formation of Raindrops: As the droplets or ice crystals grow larger and heavier, they can no longer remain suspended in the cloud.
- They fall as precipitation — rain, snow, or sleet — depending on temperature and altitude.
Types of Cloud Seeding (Based on Temperature)
- Cold Cloud Seeding:
- Used when cloud temperature is below freezing.
- Agents like silver iodide help form ice crystals that trigger precipitation.
- Warm Cloud Seeding:
- Used when cloud temperature is above 0°C.
- Commonly uses salt particles (NaCl) to promote droplet formation and coalescence.
Role in Curbing Air Pollution
- Artificial rain helps wash out pollutants like dust, smoke, and PM2.5 particles.
- Improves air quality temporarily by removing suspended particulates from the lower atmosphere.
- Useful in cities like Delhi during severe post-monsoon smog.
- Forest Fire Control: Helps in managing and suppressing forest fires.
- Also helps in:
- Reducing temperature and dryness (which worsen pollution).
- Supporting groundwater recharge and agriculture.
Challenges and Limitations
- Weather Dependence: Requires suitable moisture-bearing clouds; cannot generate rain in clear skies.
- Limited Effectiveness: Rainfall enhancement is often marginal (≈10–20%).
- Short-term Impact: Pollution reduction lasts only a few days.
- Environmental Concerns: Possible chemical accumulation (e.g., silver iodide) in soil/water.
- High Operational Cost: Aircraft, chemicals, and trained staff make it expensive.
- Scientific Uncertainty: Mixed global evidence on consistent success.
Meteorological Challenges in the Post-Monsoon Season
- The India Meteorological Department (IMD) classifies October to December as the post-monsoon season.
- During this period, rain-bearing monsoon clouds and low-pressure systems that trigger rainfall are absent.
- Winds are generally calm, and atmospheric conditions favour dry weather, except when disturbed by western disturbances at lower latitudes.
- Implications for Cloud Seeding:
-
- Cloud seeding requires mature, moisture-laden clouds for success.
- In the absence of such clouds, even seeding visible clouds may not lead to rainfall.
Past Cloud-Seeding Experiments in India
- Project: Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX)
- Conducted by the Ministry of Earth Sciences (MoES) in four phases: 2009, 2010–2011, 2014–2015, and 2017–2019.
- Trials were primarily conducted in southern peninsular India, including Solapur (Maharashtra).
- Key Findings:
- Rainfall enhancement: Up to 46% at specific locations, with an average increase of 18% over a 100 sq. km area downwind of the seeding site.
- Guidelines developed: The CAIPEEX results led to the creation of protocols and frameworks for cloud-seeding operations in India.
Global Examples
- USA: Used extensively for drought mitigation and increasing mountain snowpack.
- China: Deployed during the Beijing Olympics (2008) to control rainfall and clear smog.
- UAE: Runs the world’s largest cloud-seeding program for water security in arid regions.
- Thailand: Implements the Royal Rainmaking Project since 1955 for agriculture and drought relief.
- Australia: Conducts seeding in Tasmania to boost rainfall for hydroelectric reservoirs.
29 Oct 2025
.png)
Current Affairs
GS Foundation
Optional Course
Combo Courses
Degree Program
