Cloud Seeding Delhi: Artificial Rain in Delhi! Using Chemicals in Clouds to Reduce Pollution, Why Does It Take 15 Minutes to 4 Hours for Rain?

Cloud Seeding Delhi: Delhi’s air has once again become toxic, with the Air Quality Index (AQI) crossing 300 to reach the ‘very poor’ category. To combat this severe pollution, the Delhi government conducted a trial of cloud seeding on October 28, 2025. This technology induces artificial rain by injecting chemicals into clouds, which can wash away pollutants from the air. But the question is, why does it take anywhere from 15 minutes to 4 hours for rain to occur after this process begins?

What is Cloud Seeding?

Cloud seeding is an 80-year-old weather modification technique. It involves introducing chemical agents into clouds to induce rain or snow. Naturally, clouds need nuclei, like dust or salt particles, for water droplets or ice crystals to form. Sometimes, despite the presence of clouds, it doesn’t rain due to the lack of these nuclei. Cloud seeding provides these artificial nuclei to intensify rainfall.

• Scientific Fact: In Delhi’s case, Silver Iodide (AgI) is primarily used, which helps form ice crystals in cold clouds.
• Statistic: This technology has been shown to increase rainfall by 5-15% worldwide.

Why Cloud Seeding in Delhi?

Delhi is one of the world’s most polluted cities. During winter, PM2.5 particles from stubble burning and vehicular emissions make the air toxic. Artificial rain can wash down these particles, improving air quality. Acknowledging this, the Delhi Cabinet approved ₹3.21 crore for five trials in May 2025, and an MoU was signed with IIT Kanpur in September.

The trial on October 28th was conducted using an aircraft between 12:30 PM and 1:00 PM. Environment Minister Manjinder Singh Sirsa stated that rain could be expected soon. A total of five trials are planned, with each costing approximately ₹6.4 million.

The Complete Process of Cloud Seeding

In Delhi, the process was carried out by an aircraft. Let’s understand it in 6 steps:

1. Cloud Selection: Radar and satellites are used to identify suitable clouds at an altitude of 2-5 kilometers, containing supercooled water (water below 0°C). For AgI to be effective, the cloud temperature must be between -5°C and -20°C.
2. Seeding: The aircraft flies into the cloud and releases tiny crystals of Silver Iodide (AgI). In the Delhi trial, one aircraft deposited 10-15 kilograms of AgI.
3. Nucleation: The AgI particles act as nuclei, attracting water droplets to form ice embryos. A single AgI particle can produce 100-1000 ice crystals.
4. Growth & Coalescence: These ice crystals absorb moisture from the air and grow larger.
5. Precipitation: Once the particles become heavy enough, they fall as rain. It takes about 10-30 minutes for them to travel from the cloud base to the ground.
6. Rain Distribution: The rainfall typically covers an area of 10-50 square kilometers. The target for Delhi is 5-10 mm of rain.

Why Does It Take 15 Minutes to 4 Hours for Rain?

Cloud seeding is a ‘trigger’ for a natural process, not magic, which is why it doesn’t rain instantly. Here’s a breakdown of the timeline:

• 15-30 Minutes (Immediate Effect): Nucleation begins within 15 minutes of seeding. If the clouds are ripe, light droplets may start to fall.
• 30 Minutes – 1 Hour (Main Growth): It takes about 20-40 minutes for the ice crystals to grow to a significant size. During this time, they are carried by the wind.
• 1-4 Hours (Full Rain): For substantial rainfall, it can take 1-2 hours for large particles to form, melt, and disperse. If the wind is slow or the clouds are very high, this process can take up to 4 hours.

According to the World Meteorological Organization (WMO), 70% of cloud seeding cases show results within 20-60 minutes, while 20-30% can take 2-4 hours, depending on cloud thickness and humidity.

Success and Benefits

• Increased Rainfall: The process can increase rainfall by 5-15%.
• Pollution Reduction: It can reduce PM2.5 levels by 30-50%, potentially bringing the AQI down to the 100-150 range.
• Disadvantages: While Silver Iodide is generally considered safe, its excessive use could lead to accumulation in the soil. The process also has a 20-30% failure rate if suitable clouds are not available.