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Cloud Seeding : Impact and Examples

• Cloud Seeding is a process to induce rain in moisture-filled clouds by sprinkling the upper reaches of clouds with chemicals such as common salt or silver iodide, usually with the help of jets fixed to airplanes.
• Usually, rain occurs when moisture content in a cloud becomes too heavy and can no longer be held. Cloud seeding aims to accelerate this process by making more chemical nuclei available to facilitate the process.
• The chemicals induce nucleation – the water in the cloud condenses around the newly introduced particles, and then goes to form ice.The much heavier ice particles then melt on their way to the ground.
• For cold clouds, sodium iodide crystals are used and for warm clouds – such as those in India – common salt crystals are used.
• Rain generally follows 30 minutes after the seeding. But the process is only meant to increase the precipitation and rainfall isn’t guaranteed.

Examples of cloud seeding:
• In July this year, China allocated 199 million yuan ($29.76 million) to spend on its cloud seeding program to prevent drought.
• During 2008 Beijing Olympics, Chinese organizers fired a barrage of rockets in the air ensuring clear skies for the opening ceremony.
• In 2009, Chinese scientists fired Beijing skies with iodide sticks hoping to end a long spell of drought, the seeding, however, caused an early snowfall which disrupted air and road traffic.
• In the United States, cloud seeding is occasionally used by ski resorts to induce snowfall. Cloud seeding is being used to recharge the ground water in arid UAE.
• Last year, Malaysia and Indonesia used cloud seeding to stimulate rainfall after toxic smoke gripped the region. Effectiveness of cloud seeding:
• The success of cloud seeding depends on the weather conditions of the area. Some moisture in the atmosphere is needed to cause precipitation.
• Environmentalists have raised concerns regarding secondary air and water pollution as an outcome of chemicals used to cause precipitation.

Why Cloud seeding was not an option for tackling Delhi pollution?
1. Cloud seeding requires moisture laden clouds and there are none at the moment over Delhi.
2. The wide area of Delhi requires massive amounts of resources, which just to pull together, could take months.Seeded clouds may not give rain immediately and could possibly travel out of the desired region thus wasting the entire exercise.
3. Cloud seeding does not guarantee rain. It always remains to be a matter of chance.
4. The science of cloud seeding has not been established yet, hence requires further refinement.

Impact on environment and health:
• Silver iodide can cause temporary incapacitate or possible residual injury to humans and mammals with intense or continued but not chronic exposure.


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