But the success of such an attempt depends on a host of conditions ranging from the presence of clouds to their moisture content and from the way they are seeded to when.

Rainfall, which is usually brought by western disturbances in winter, is expected to wash away pollutants. Cloud seeding involves spraying a mixture which includes salts into a cloud, in this case from an aircraft, to allow “cloud drops” to form around the nuclei that the salts provide, and eventually drop down as rain.

Manindra Agrawal at IIT-Kanpur, who is the project in-charge, explained favourable conditions would be clouds with “reasonable moisture content” – but whether conditions would be amenable to it given this time of year would play a significant part.

“As of now, radar data shows that around that period (around November 20), there will be clouds. But these things change. It will be incorrect to say that we will do it on November 20 or 21, because in a week’s time, it’s possible that updated information shows that clouds may not be there,” he said.

“In the winter, you do get clouds occasionally. Sometimes, although rarely, it does rain also. What we will be doing is increase the chance of rain whenever there are clouds. These are scientific experiments…it depends on clouds and moisture content in the clouds,” he added.

Sachchida Nand Tripathi, Professor at IIT-Kanpur, who is part of the project, said IIT-Kanpur had two significant pre-requisites for the procedure – including a Cessna aircraft – with seeding equipment installed aboard.

And especially, the professor added, IIT-Kanpur has developed the ‘seed’ – the solution on which cloud droplets form needs to have cloud condensation nuclei and ice nuclei, which comes from two different salts.

“Where and at what height you seed then depends on meteorological conditions and cloud-related properties,” he said.

According to Agrawal, clarity on conditions becoming favourable for cloud seeding was possible closer to when the process was scheduled to be carried out; three days ahead of the chosen time for it could shed light on whether or not the required conditions were available for it. This too, however, was subject to variation.

“That picture also keeps changing as you come closer. If we know three days ahead that there is a chance, we can make all the arrangements, park the aircraft in Delhi and then wait. On the day we want to fly, we would have to get detailed data and see,” he said.

How is it done?

The process, according to Agrawal, would ideally require flying into the cloud to measure its moisture content and adapt the seeding technique in regard to it – but there was also a measure of uncertainty involved.

“Once we know (the moisture content) we tailor our spraying accordingly. If there is less moisture content, we spray more. If there is more moisture, we spray less. But that kind of instrumentation (to measure moisture) we don’t have now, and we will have to fly a little blind there, which is what makes it more uncertain,” he added.

But what about the extent of the area over which the process could be carried out, the duration of seeding it would require and the expenditure that this would entail?

“If we get the kind of cloud cover we need, we would like to do 300 sq km. Delhi is around 1500 sq km, so if a reasonable part of that we can seed… The estimated cost is around Rs 3 crore, but we will know better once we do the experiment,” he said.

The procedure would, however, require permissions. “Many permissions are required to fly the aircraft in Delhi airspace. For 300 sq km, it can take 9 to 10 hours to spray the mixture – it is a very finely ground solid mixture,” he said.

“The flares that are made that contain this mixture – there is a company in Sivakasi, which makes these flares for other parts of the world as well, and they are doing this for us,” he also said.

To spray the salt mixture, according to Agarwal, aircraft would be required to fly below the clouds. He also flagged issues that needed to be factored in with regard to the altitude of the aircraft carrying out the procedure.

“If you just spray it from below, some will go up, and some will naturally fall by gravity. One can go up above the cloud and spray it, but clouds are often thick, and that would mean going very high. You don’t want to go inside the cloud because there will be turbulence,” he said.

“So, what is done is that you fire the flares – that generates heat and then you eject the mixture. Hot air rises, and it takes the entire mixture up into the clouds,” he added.

Previous trials

Earlier attempts at cloud seeding have already been made at IIT Kanpur, he said, with much success – but when weather conditions were more amenable.

“This exercise was done in the July, August, September period this year, but it did not intend to cause rain. The intention was to get DGCA’s approval for air worthiness of our aircraft, which was modified due to flare attachments that were put on the wing,” he said adding that it was carried out during the rainy season.

“Even if there was precipitation, it would be hard to argue that it was because of seeding…The seeding that we did was in 2018 at IIT Kanpur in the months of April and May, when there are no rains usually. We conducted six trials and five of them resulted in rain,” he also said.

Back then, said Agrawal, seeding was limited to a smaller area with the intent to gauge whether the set-up at their disposal actually worked. “It did cause rain, but not in a large area…not that it caused rain all over Kanpur city, but it did in some parts,” he said.

The trial had in fact, resulted in not only a “non-trivial” period of rain, but even hail. “There was a short, but non-trivial period of good rain – at least a 10-minute period of decent rain, and then very light rain, a drizzle over the next hour or so. We even got hail – when we spray too much, the particles start coalescing and instead of a drop, it becomes a bigger piece – hail,” he said.

This, however, was in the pre-monsoon season – not winter. “We did get success there. We have never actually done this in the winter… there is always a question mark,” he added.