Can artificial rain work in Delhi? Expert Raghunandan answers

Delhi is about to run its first major trial of artificial rain through cloud seeding around mid-October, as announced by Environment Minister Manjinder Singh Sirsa. The Delhi government has sanctioned Rs 3.21 crore for the project, which includes five cloud seeding trials to combat air pollution.

In an interview with The Federal, D Raghunandan of the Delhi Science Forum (DSF) and former president of the All India People's Science Network (AIPSN), explains how the process works and whether it is effective.

Could you explain to us in simple terms how artificial rain is created and how cloud seeding works?

The idea is that you drop some particles of dry ice, etc., from an airplane or a balloon, which will make the moisture in clouds dissipate like it happens during rain. It will encourage the formation of particles around which the water vapour can form into droplets and fall down as rain. Now, that's the principle, but in order for it to actually happen, there are many, many things that are required.

First, the cloud must have sufficient moisture for this to work. If you have a thin, discrete cloud which disappears as you are watching it, nothing is going to happen. So, you need clouds with at least 50 per cent moisture content, which, as you can well imagine, is not something that happens all the time. It happens only occasionally.

Secondly, you need to have appropriate conditions in the atmosphere and in the weather system. So, you must have a reasonable wind, but not such a strong wind that the cloud gets blown away.

The cloud should be situated over where you want rainfall. Then, the temperature inside the cloud needs to be right, and what you use for cloud seeding, the chemicals or whatever, are designed or selected appropriate to the conditions inside the cloud. So, if you have cold clouds, then you use a certain kind of chemicals. If you have warm clouds, then you use certain kind of chemicals. So, that is the other condition that is required. Then, atmospheric conditions should be appropriate for cloud seeding to work.

Also read: How climate chaos is rewriting India’s water future

So, how do we know cloud seeding has worked, and to what extent has it worked?

Most studies that have been conducted show that if there is a chance of rainfall, the amount of rainfall can be 3 to 5 per cent more than it would have been otherwise. So if you have a 30 per cent chance of rainfall, according to the Met office, maybe those chances increase to 33 per cent or 34 per cent.

The problem is that these parameters to judge whether cloud seeding has worked and if it has worked, how much it has worked, till now have never been substantiated statistically. That is, if I do 10 trials, do I get a 3 per cent improvement in rain in 8 out of 10 trials? We don't know. Is it only once or twice out of 10? Then, it's not sufficient to say, yes, it has worked.

So, my worry is in these trials over Delhi, how are we going to judge whether it has worked or not? Straightaway, one can say, okay, it was not rainy. The Met office did not predict rain. Now, it is raining, so it worked. But under the same conditions, tomorrow, will it work? We don't know. So, these are the many questions that surround cloud seeding. It is slightly uncertain. It requires a lot of other conditions to be right in order for it to work. And you must have scientifically verifiable parameters according to which you can judge whether it has worked or not.

Also read: Over 7,500 evacuated as Yamuna floods Delhi’s low-lying areas

You said the kind of substances or chemicals that are used for cloud seeding depends on the composition, the kind of cloud it is. What are these substances? And are there any risk factors?

One of the materials used for cloud seeding is dry ice, which is solid carbon dioxide. It’s like ice, which is used in deep freezers like ice cream trolleys. They are relatively harmless. Common salt is used for cloud seeding. That is relatively harmless. Silver iodide is used for certain kinds of clouds, cold clouds in particular. Excess of some of these chemicals, of course, is not very healthy. There are some potential risks, particularly if it is not just a one-day trial. If you are going to do repeated cloud seeding over two weeks or three weeks, then it becomes maybe a partial problem.

Also read: Delhi: AAP slams BJP over artificial rain, warns of protest

Earlier, you said clouds need to have some moisture to work. The Delhi government has already postponed the schedule of the trial twice, and it's shifted now to mid-October. Do you think that Delhi's atmosphere and weather at that time will be conducive to such a trial?

I am not a meteorological expert or a weather expert, but from what I understand of the weather, the original idea of doing it during the monsoon is clearly wrong. Because in the monsoon, it's going to rain anyway. So, who is to say whether cloud seeding has helped the rain or not? So that was a useless test, if you ask me.

My understanding is that peak pollution in Delhi is during December and January. That's when the media goes crazy and writes articles every day about the farmers in Haryana burning stubble, etc. AQI goes above 400, 500. Now, during that winter period of December, January, and February, the sky over Delhi is usually very dry, not moist. There aren't many clouds to be seen. And even if there are clouds, they're not likely to be laden with the moisture. So winter is, I would think, not a great time to attempt cloud seeding. But winter is the time when Delhi needs it the most. So, I don't see that cloud seeding in the month of October is going to do much good. Because by October, the monsoon conditions have passed, and moisture-laden clouds are going to be few. Plus, the question remains, why do you want rain during October? The point of this trial is to reduce pollution. So, I don't see this as a particularly appropriate test. If at all you want to try something, do it during December and January and see what happens.

Also read: Here’s all about the science of cloud seeding

Can you tell us where all within the country and outside have these experiments been done before, and whether they have helped with air pollution?

There have been experiments done in the US and in the UK. Famously, experiments were done during the Beijing Olympics. When the city of Beijing wanted to prevent pollution around the city. And also prevent much rainfall around the city. So, what they did was they followed the clouds before the clouds entered Beijing to bring the rain down earlier, so you don't have clouds during the opening ceremony.

There is no scientific evidence to show how much that works. We can only say that fortunately, it did not rain during the opening ceremony in Beijing. Whether that was because of the cloud seeding or due to other factors, we can't say with any definitive knowledge. So as I said, if you look at all the cloud seeding experiments worldwide and then do a statistical analysis, the net result comes out to be a 3 to 4 per cent increase in precipitation as a result of cloud seeding. In the US, cloud seeding has been done to combat drought… It has not been convincing enough to say – let's do it every year, and we'll make sure that we have rain.

Also watch: Why Delhi is banking on artificial rain to tackle smog

Overall, would you say that artificial rain or cloud seeding is an effective measure against air pollution?

My own assessment is that I don't see cloud seeding as a permanent solution. The way the government is talking about it suggests, we'll go up, we'll spray some chemical, and voila, there will be rain over Delhi. Like it’s a magic wand. The problem is that the Delhi government is after silver bullet solutions to the problem of pollution. They first tried smog guns, which is nothing but spraying water. Now they’re trying to bring rainfall over the whole city.

Unfortunately, it is not just the Delhi government that put forward this magic formula. I think it is also the Honourable Supreme Court, which virtually ordered the Delhi government to set up smog guns, which I think has been one of the most spectacular failures in anti-pollution policy, but which are still continuing.

The Central Pollution Control Board is on record as saying that cloud seeding is not a solution to the problem of air pollution. I don't think you can get a better authoritative source than the CPCB on this subject.

What do you think are the long-term policy measures that a government that is serious about combating air pollution should undertake?

The government and other people in power, including, unfortunately, the Supreme Court, are looking for magic solutions to the problem of air pollution, whereas the solution is staring you in the face – which is to reduce the number of vehicles on the road. We know that more than 60 per cent of air pollution in Delhi is caused by vehicles. If that is the case, all policies must be directed to reduce the number of vehicles on the road and the only way to do that is to substitute personal vehicles by public mass transport, because one bus carries 50 people, compared to one car which is carrying one person and the pollution, road occupations, fuel consumption, everything on a per capita basis is 10 times worse in personal vehicles than it is in public transport.

That’s the real solution. But to tackle it, the government and political class will have to tackle the automobile lobby. And that’s not easy. So to escape from doing that, you go looking around for smog guns, rain seeding, etc.