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Ecology & Environment
Mahesh

20/11/24 09:02 AM IST

Artificial rain in New Delhi

In News
  • As the national capital’s air quality continued to be in the ‘severe plus’ category for the third consecutive day, Delhi Environment Minister is  seeking clearance for allowing artificial rain in the region.
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.
  • 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.
Conditions for Cloud Seeding
  • 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.
  • In winter, you do not see the kind of clouds that are needed for seeding, but western disturbances are the way through which clouds form.
  • Even if clouds are there, you need to see what their height is, what their liquid water content is.
  • 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.
Importance
  • Pollutants such as PM2.5 and PM10 can be washed out to a significant extent by prolonged rainfall.
  • However, other pollutants like ozone and sulphur dioxide are not affected.
  • Besides, cloud seeding or artificial rain can severely impact the environment.
  • For instance, the chemicals used — such as silver iodide — in the process can adversely affect agriculture and the ecosystem if they accumulate in soil and water in large quantities.
  • Scientists are yet to fully understand the impact of these chemicals on the environment.
  • The water vapour used in the process would have naturally precipitated elsewhere, and it potentially deprives other regions of rainfall.
  • This artificial manipulation of weather patterns could even lead to droughts in areas which would have received this rainfall otherwise.
Source- Indian Express

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