How successful is cloud seeding technology?

Context

Haryana Deputy Chief Minister Dushyant Chautala has written to Prime Minister Narendra Modi, requesting him to “undertake cloud seeding plan to combat the air pollution engulfing Delhi and NCR”.

About

  • Cloud seeding is a kind of a weather modification technology to create artificial rainfall. It was pioneered by atmospheric scientist Bernard Vonnegut.
  • It works only when there are enough pre-existing clouds in the atmosphere.
  • Rain happens when moisture in the air reaches levels at which it can no longer be held, and cloud seeding aims to facilitate and accelerate that process by making available chemical ‘nuclei’ around which condensation can take place.
  • These ‘seeds’ of rain can be the iodides of silver or potassium, dry ice (solid carbon dioxide), or liquid propane. The seeds can be delivered by plane or simply by spraying from the ground.
  • It is also known by other terms such as man-made precipitation enhancement, artificial weather modification, and rainmaking.

Where all has it been tried earlier?

  • Cloud seeding is not new to India and it has earlier been attempted in Karnataka, Andhra Pradesh and Maharashtra to address drought.
  • Similar experiments of cloud seeding had earlier been tried in Australia, America, Spain and France.
  • In United Arab Emirates, the cloud seeding technique led to creation of 52 storms in Abu Dhabi.
  • Also, such seeding is routine in Russia and other cold countries where the technique is used to disperse fog at the airports.

Cloud Seeding Methods

There are three cloud seeding methods: static, dynamic and hygroscopic

  • Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense. The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.
  • Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain. Up to 100 times more ice crystals are used in dynamic cloud seeding than in the static method. The process is considered more complex than static clouding seeding because it depends on a sequence of events working properly.
  • Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them.

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