Government plans to induce artificial rains to beat pollution. How does it work, explained

Representatives of the central and Delhi government said they are planning to induce artificial rain to wash away toxic pollutants from the air. What is artificial rain? How is it created? Does it work? Here is a ready reckoner:

Artificial rains or cloud seeding is defined as an effort to chemically impregnate clouds to increase rainfall.

Artificial rain is created by rocket-launching chemicals, such as silver iodide, into clouds to boost rain. To seed a cloud, pilots introduce a chemical agent, commonly silver iodide. It draws moisture to itself, allowing the cloud’s water vapour to condense into droplets and produce rain, according to the World Meteorological Organisation (WMO).

To cope with searing global temperatures, protracted droughts and chronic water shortages, countries from the United States to China are turning to “cloud seeding”, which aims to boost rainfall in dry areas.

The process is hardly new. First trialled in the United States around World War Two, it is now discreetly used in more than 50 countries, from Mali to India and Puerto Rico.

In 2016, 56 countries had cloud seeding operations, compared to 42 in 2011, as estimated by the World Meteorological Association.

China, however, has the biggest cloud-seeding operation, which it utilises not only to increase rainfall but also to avoid hailstorms that can devastate farm crops.

The country even has an office of weather manipulation.

The programme is increasingly used to disperse smog in heavily polluted regions.

Before Beijing hosts prestigious guests or events, there is often heavy rainfall which has the effect of clearing the city’s heavily polluted air for a few days. Many locals credit the meteorological bureau for the rainstorms.

It is also used to battle China's crippling water scarcity, which threatens a long-standing policy of self-sufficiency in food production, as demand from manufacturing and power generation grows.

Well … umm ..

“There are still a lot of unknowns and a lot more research to be done,” Deon Terblanche, the WMO’s director of research. “But... if it can be done successfully it will have huge benefits, especially in water-scarce areas,” he told Reuters last year.

Although the amounts of silver iodide used for most cloud seeding are too small to hurt the environment or public health and do not present any significant risk, he said, the chemical in very large quantities can be toxic.

Apart from environmental risks, cloud seeding could also lead to geo-political spats if over-used in one region, depriving areas downwind of rainfall.

The main stumbling block, however, is measuring the technique’s success.

Terblanche said in some areas where cloud seeding is used, rainfall has increased by more than 10 percent. But there could also be knock-on effects that are harder to quantify, such as increased river runoff, he added.

Terblanche believes cloud seeding shouldn’t be seen as the best way to deal with water shortages. In particular, countries need to work on capturing and managing natural rainfall to take advantage of heavier downpours, as rain becomes less reliable.

While the success of cloud-seeding efforts remains in question, commercial use of the technology is growing. US and European companies are testing unmanned drones to seed clouds, and promising rain-free wedding ceremonies by ‘bursting’ clouds ahead of the big day.

Still, the technology can’t do much to tease rain from a cloud-free sky, experts warn.

“In extreme heat or drought conditions, there are no clouds. Nobody can make clouds,” Roelof Bruintjes, a senior scientist who works on weather modification for the US National Center for Atmospheric Research told Reuters last year.

Rather, the idea of cloud seeding is to make rain form more efficiently inside clouds so more water comes down, he said.

Such artificial rainmaking is akin to giving clouds vitamins, or farmers applying fertilisers to boost their crop yields, he explained.