Delhi govt plans ‘cloud seeding’ to induce rains amid pollution: What is this process?
Context- The Delhi government had announced earlier this week that it was considering cloud seeding or ‘artificial rain’ to wash away pollutants in the air.
The now mooted proposal has been attempted previously in India but only in the monsoon season – when clouds with moisture are present – and pre-monsoon months. Besides, it has only been done before in the country with the purpose of bringing rainfall to drought-prone areas, and not to mitigate pollution.
What is cloud seeding?
- Water vapour condenses around small particles to form the droplets that make up a cloud. These droplets collide and grow; as they get heavy and the cloud gets saturated, it rains.
- With cloud seeding, clouds are usually injected with salts like silver iodide, potassium iodide, or sodium chloride, which is the ‘seed’. These salts are expected to provide additional nuclei around which more cloud droplets can form. They are dispersed into the cloud either using aircraft or through generators on the ground.
What exactly is the mechanism and how is it expected to help bring down the concentration of pollutants?
- Seeding accelerates cloud microphysical processes. You need sufficiently large droplets that can reach the surface of the earth and not evaporate on the way
- The substance that is dispersed into the cloud needs to have cloud condensation nuclei and ice nuclei and these two come from two different salts. The cloud condensation nuclei help form cloud droplets, and ice nuclei help to form ice crystals. Ice crystals grow faster than drops, and they become large and fall.
What are the conditions required for cloud seeding to be done?
- Firstly, cloud cover and clouds of a certain type are necessary.
- M Rajeevan, former secretary of the Ministry of Earth Sciences, said, “Cloud seeding can only happen if there is a sufficient number of clouds and a particular depth to these clouds. Inside, there needs to be an adequate number of cloud droplets.
- Cloud seeding is done to increase the radius of the cloud droplets so that they will grow bigger and because of gravity, they will come down as rainfall. But with a clear sky, you can’t do it.”
- In winter, clouds form over Delhi when a western disturbance moves over the region. These are storms that originate in the Caspian or Mediterranean Sea and bring non-monsoonal rainfall to northwest India.
- With a stable atmosphere in winter, clouds are expected to form when a western disturbance disturbs this stability of the atmosphere.
- While the possibility of cloud formation can be determined in advance through radars, other conditions will have to be studied on the day seeding is likely to be done.
Has cloud seeding been done before in India, and has it been successful?
- Seeding has mostly been attempted during the monsoon in India, in places such as Karnataka, Maharashtra and Tamil Nadu.
- A more recent experiment, the fourth phase of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX-IV) that took place in the monsoon seasons of 2018 and 2019, was conducted in drought-prone Solapur in Maharashtra. It pointed to a relative enhancement of 18 per cent in rainfall.
- In 2018, cloud seeding was floated as a proposal in Delhi but it didn’t happen, with the many permissions that were required coming in the way, along with the absence of seeding equipment on IIT Kanpur’s own aircraft.
Is it expected to help with pollution levels?
- In India so far, cloud seeding has not been tried with the purpose of reducing pollution, but only been tried to deal with drought-like conditions.
- Thara Prabhakaran, a scientist at the Indian Institute of Tropical Meteorology (IITM) said “There are a few cases where China tried weather management options. In India, we don’t have investigations done in this aspect (impact of cloud seeding on pollution). Our conditions are different, and we will need a dedicated study on this. Clouds and their processes are very complex, these are non-linear processes.
- If you do something, it is not known exactly that it is going to give you this much rain or not. Clouds are also able to rain naturally, so how do you separate natural rain from seeded rainfall?”
Conclusion – Still there are a lot of difficulties. Cloud microphysics is more complicated than we think. We can get some advantage from it in the monsoon season if there are enough clouds. When you seed, all clouds won’t rain, and even without seeding clouds can rain. It is still a very complex and uncertain field of research.
Syllabus- GS-3; Environment
Source- Indian Express
