CPCB mulls cloud seeding to trigger rain, experts sceptical

EXPERIMENTAL Scientists say cumulus clouds needed for rain usually do not form in winter season

NEWDELHI: The Central Pollution Control Board (CPCB), with the help of scientists from IIT Kanpur, is mulling artificial rain with cloud-seeding technique this winter to bring some respite from pollution.

But a section of experts say the method may not be fruitful during winter, when pollution reaches abysmal levels.

However, if the pilot project is successful then it would be a rare feat because across the world, cloud seeding is usually done during summers or the rainy season, when there is ample cloud cover.

“Barring a few instances in other countries, cloud seeding is usually done during the summer months. We would conduct the experiment during winter and that too with fully indigenous technology. A few other states in India had conducted such experiments but with foreign technology,” said SN Tripathi, head of the civil engineering department at IIT Kanpur and one of the brains behind this project.

This is where a section of scientists and weather forecasters have expressed their doubts.

They said that while on one the hand, there is hardly any cloud cover over northwest India during winter, on the other hand, not all clouds can be seeded.

“The primary requirement for cloud seeding is the availability of cloud itself. In northwest India, there is hardly any cloud cover during the winter season. Secondly, not all clouds can be seeded to trigger rain. These include low-altitude stratified clouds and high-altitude cirrus clouds. Matured cumulus clouds, which have good dimension and water content, can be considered for triggering rain with seeding,” said LS Rathore, former director general of the India Meteorological Department (IMD).

But matured cumulus clouds usually do not form during winter in northwest India and Delhi.

A senior IMD official said that on November 22, there is some possibility of cloud formation. But those would be not suitable for seeding as they are high clouds.

“Chances of formation of large cumulus clouds are very rare in the next one week at least. Such clouds usually form during the summer seasons when there is high temperature and moisture content is also high,” said GP Sharma, president (meteorology and climate change) of Skymet, an Indian private weather forecasting agency.

Cloud seeding is the process of injecting chemicals such as silver iodide, dry ice and liquid propane. These chemicals not just reduce the temperature of the water vapour molecules, thus helping in precipitation, but even provide a platform on which the water droplets can coalesce. When they become heavy, they come down as rain.

“Cloud seeding has experimented only with matured clouds that are laden with water particles. But whether rain can be triggered from other types of clouds, which sometimes come

The primary requirement for cloud seeding is the availability of cloud itself. In northwest India, there is hardly any cloud cover during the winter season. Secondly, not all clouds can be seeded to trigger rain.