Cloud Seeding & Its Effectiveness – Explained Pointwise

Recently, the Delhi government, in partnership with IIT Kanpur, has recently  implemented artificial rain experiments (cloud seeding) as an emergency measure to combat its chronic air pollution crisis.

What is Cloud Seeding?

• Cloud seeding is a form of weather modification aimed at enhancing precipitation (rain or snow) from naturally forming clouds by dispersing specific chemical agents into the atmosphere.

• This process is employed to increase rainfall in drought-prone regions, suppress hail, clear fog, and—more recently—attempt to mitigate airborne pollution by “washing out” particulates.​

• Chemical Agents Used: The most common chemicals are silver iodide, potassium iodide, dry ice (solid CO₂), and sometimes table salt. These agents act as cloud condensation nuclei or ice nuclei, enabling water vapor in clouds to coalesce and form larger droplets or ice crystals.
• Mechanism: The introduced particles mimic natural nuclei, prompting supercooled water droplets to freeze and aggregate, ultimately becoming heavy enough to fall as rain or snow.

Key Cloud Seeding Methods:

Effectiveness of Cloud Seeding:

1. Precipitation Augmentation: When suitable clouds are present, seeding can typically increase rainfall or snowfall by 10% to 15% in the targeted area. In some specific, ideal scenarios, increases have been reported to be as high as 20% to 30%.
2. Snowpack Enhancement: It is highly effective in increasing mountain snowpack, which acts as a natural water reservoir. This is critical for hydropower generation and downstream irrigation in the spring. Regions like the Rocky Mountains in the US and mountainous regions in Australia have used this successfully for decades.
3. Hail Suppression: By introducing numerous condensation nuclei, the process can cause the water droplets to freeze into many small ice particles rather than a few large ones. These small particles melt before hitting the ground, thus reducing the size and damage potential of hail.
4. Fog Dispersal: In cold conditions, seeding can clear supercooled fog at airports, improving visibility and flight safety.

Challenges related to Cloud Seeding:

1. Requires Clouds, Not Creation: Cloud seeding cannot create clouds from clear skies. It is 100% dependent on the presence of existing clouds that contain enough liquid water and are at the right temperature (often supercooled water). If the atmosphere is too dry or stable, seeding has no effect.
2. Atmospheric “Thirst”: Even if rain is generated, if the air mass below the cloud is very dry, the falling precipitation may evaporate before reaching the ground—a phenomenon known as virga.
3. High Cost: Running a sustained cloud seeding program is expensive. It requires specialized aircraft, ground stations, radar monitoring, and a team of meteorologists and pilots. This makes it an impractical or non-sustainable solution for long-term water management.
4. The “Rain Stealing” Controversy: This is the most significant political challenge. The downwind regions often accuse seeded areas of “stealing” their water, claiming that forcing clouds to precipitate early depletes the moisture that would have naturally fallen elsewhere. While evidence for this is inconclusive, the perception creates interstate or international political friction.
5. Chemical Dispersion (Minimal Risk): While Silver Iodide is the most common agent, some public concern remains about dispersing chemicals into the environment. However, the amounts are minute (parts per trillion), and scientific studies have generally concluded that silver iodide is not environmentally hazardous at the concentration levels used in cloud seeding.

Reasons for underperformance of cloud seeding in Delhi:

1. Insufficient Cloud Moisture: Successful cloud seeding requires clouds with high moisture content (usually above 50%) to allow chemical nuclei to facilitate droplet formation. During Delhi’s trials, moisture levels were only about 15-20%, too low for effective rainfall induction.
2. Unfavourable Weather Conditions: Cloud seeding is highly dependent on specific meteorological conditions, which were not met during the trial periods.
3. Expectations v/s Reality: Cloud seeding is not guaranteed to produce rain—its success rate is variable, and it is better seen as a supplementary, emergency intervention, not a primary solution.

Conclusion: Cloud seeding is a promising tool for weather modification, drought management, and air quality control, but its success depends on cloud properties, timing, and atmospheric conditions. While potential is high, scientific debate continues over its practical effectiveness and long-term impact.