While chief minister Arvind Kejriwal suggested using cloud seeding for inducing rain to clear away the smog that has enveloped the Capital since Diwali, experts are divided on its effectiveness given the timing and Delhi’s usually dry weather.
Here’s all you need to know about cloud seeding:
What is cloud seeding?
It is a process to induce rain in moisture-filled clouds by sprinkling the upper reaches of clouds with chemicals such as common salt or silver iodide, usually with the help of jets fixed to aeroplanes.
Usually, rain occurs when moisture content in a cloud becomes too heavy and can no longer be held. Cloud seeding aims to accelerate this process by making more chemical nuclei available to facilitate the process.
The chemicals induce nucleation – the water in the cloud condenses around the newly introduced particles, and then goes to form ice. The much-heavier ice particles then melt on their way to the ground.
For cold clouds, sodium iodide crystals are used and for warm clouds – such as those in India – common salt crystals are used.
Rain generally follows 30 minutes after the seeding. But the process is only meant to increase the precipitation and rainfall isn’t guaranteed.
How effective is it?
The technology was first invented in the United States in the 1940s but its success rate has been patchy, especially in areas with a warm weather. Several countries, including China, France and Australia, have tried to induce rain with seeding but with various degrees of success.
Australia, for example, found that the technology was ineffective in the plains but successful over the island, Tasmania – probably because of increased moisture levels.
The most enthusiastic user of the technology is China, which has pumped in millions of dollars -- $150 million a year, by some estimates -- into cloud seeding and exports machinery to other countries, including India.
Beijing has used the weather modification technology to induce rain, clear away pollution and even inhibit precipitation – like during the 2008 Olympics, when it overseeded clouds to inhibit storms/rainfall and ensured clear skies for sports.
Experts also warn of secondary air and water pollution as an outcome of chemicals used.
But the bigger problem is, there is simply no effective metric to determine whether the rainfall after seeding a cloud would have fallen anyway.
How has it worked out in India?
India’s experiments with modifying rainfall first started in 1951 over the Western Ghats but saw a spurt in recent years with states such as Andhra Pradesh, Karnataka and Maharashtra opting for trial runs of the technology.
Last year, Maharashtra conducted a cloud seeding run after August to reverse the effects of drought but it wasn’t very effective because most of the moisture-laden clouds had withdrawn by then. Similarly, experiments by previous governments in Karnataka had largely failed.
This year, the Maharashtra government had earmarked Rs 30 crore for cloud seeding but shelved the project after above-average rainfall.
Will it work in Delhi?
Unlikely, experts say, because of the Capital’s dry weather and the time of the year, when moisture in the air isn’t very high. Cloud seeding works best just before or during the monsoon, which receded from northern India at least two months ago.
As winter approaches, the number of moisture-laden clouds decreases and in the absence of these, cloud-seeding is unlikely to succeed. This, combined with the technology’s patchy record, don’t hold good news for Delhiites. The chance of rainfall washing away pollution and the blanket of haze hanging over the city is little.