Combating air pollution with artificial rain: Cloud seeding explained

The Delhi govt has announced it would initiate cloud seeding to tackle air pollution in the national capital

The Delhi government announced it would initiate cloud seeding or "artificial rain" to wash away pollutants in the air in the national capital. The Arvind Kejriwal-led government said it will bear the entire cost of artificial rain to combat hazardous air pollution in the city.

What is cloud seeding?

Cloud seeding is a weather modification technique to enhance precipitation by dispersing substances into the air that help to saturate the clouds.

The process starts with identifying suitable clouds through weather analysis using aircraft or ground-based generators. Following this, seeding agents are released into the targeted clouds. The seeding particles help in the formation of larger water droplets, which leads to increased rainfall.

 

To initiate cloud seeding, clouds are injected with salts such as silver iodide, potassium iodide, sodium chloride, or dry ice (solid carbon dioxide), which acts as the "seed". These salts are dispersed to provide additional nuclei around which more cloud droplets can form.

What are the methods of cloud seeding?

1. Hygroscopic cloud seeding:

Hygroscopic cloud seeding involves dispersing salts through flares or explosives in lower portions of clouds. Following the dispersal, the salts grow in size. This method usually involves table salt. Hygroscopic cloud seeding has proved to have positive results in research conducted by countries such as South Africa and Mexico.

2. Static cloud seeding:

In 2010, researchers from the University of Geneva directed infrared to the air above Berlin. The experiment showed that infrared can help atmospheric sulfur dioxide and nitrogen dioxide form particles that act as seeds and cause rainfall.

3. Using salts:

Termed the most common method, chemicals such as silver iodide, potassium iodide and dry ice are dispersed using an aircraft or by dispersion devices located on the ground.

What are the applications of cloud seeding?

1. Agriculture:

It helps to create rain, which can provide relief to drought-stricken areas.

For example, the Karnataka government, in 2017, launched "Project Varshadhari", under which an aircraft was used to spray chemicals to induce rainfall. The project covered Bengaluru, Gadag and Yadgir districts of the state.

2. Power generation:

The cloud seeding method has been shown to augment the production of hydroelectricity in Tasmania, Australia, during the last 40 years.

3. Water pollution control:

The process of cloud seeding can maintain minimum river flows and dilute the impact of treated wastewater discharges from industries.

4. Fog dispersal and cyclone modification:

During winters, cloud seeding is initiated to increase the mountain snowpack to ensure that additional runoff is received during the spring melt season.

The US in 1962 launched "Project sky water", aimed at fog dispersal, hail suppression, and cyclone modification.

5. Tackle air pollution:

The method of cloud seeding can be used to settle down toxic air pollutants through inducing rain.

For example, recently, the Central Pollution Control Board and other researchers discussed the possibility of using cloud seeding to tackle Delhi's air pollution.

What are the challenges involved in cloud seeding?

1. Side-effects:

The chemicals used in cloud seeding may cause harm to plants, animals, people, and even the environment.

2. Abnormal weather patterns:

It may lead to changes in climatic patterns, like places that receive rains may experience drought conditions due to the artificial process of adding chemicals to the atmosphere to stimulate rain.

3. High cost:

Cloud seeding involves dispersing chemicals to the sky using aircraft or flare shots, which involves huge costs and logistic preparations.

4. Pollution:

Following the initiation of cloud seeding, the rain that falls will include seeding agents such as silver iodide, dry ice, or salt. The residual silver discovered in places near cloud-seeding projects is considered toxic.

Which countries have used the cloud seeding method?

1. Thailand:

In November 1955, Thailand launched the "Thailand royal rainmaking project" to help farmers suffering from severe drought.

2. China:

China has the largest cloud seeding system, where they increase the amount of rain by firing silver iodide rockets into the sky. In February 2009, China fired iodide sticks over Beijing to artificially induce snowfall after four months of drought and blasted iodide sticks over other areas of northern China to increase snowfall.

3. India

In 1983, 1984–87, and 1993-94, the Tamil Nadu government initiated cloud seeding to deal with severe drought. In 2003 and 2004, the Karnataka government initiated cloud seeding.

4. Israel

Israel has been using cloud seeding since the 1950s. It disperses silver iodide from airplanes and ground stations.

Several other countries, such as Russia, Australia, and the UAE, have experimented with cloud seeding.