Brilliant rain plan still in the clouds

Hyderabad: Even as city reservoirs run dry and groundwater levels remain at a record low, the state government does not have any plans of seeding clouds, which will induce rainfall.

Experts say this is the best time for cloud seeding given the low pressure area over Bay of Bengal and the upper air trough from Vidharbha to Tamil Naidu crossing Telangana, accelerating heavy cloud formation.

Dr M. Subbarao, academic advisor — JNTU — Centre for Atmospheric Sciences & Weather Modification Technologies on Cloud Seeding, said, “The clouds are categorised as low and medium depending on their height. Though they contain water, it won’t condense into rain as they lack ‘cloud condensation nuclei’ (CCN), also known as cloud seeds. CCN are small particles on which water vapour condenses. Cloud seeding is nothing but injection of CCN from planes so that water vapour in the clouds turn to rain.

“Earlier chalk power was sprinkled, but the clouds would take a long time to transit and move away, later common salt was used, but it is a hygroscopic substance (catches moisture fast). Years later they settled on calcium chloride, which proved to be the best, especially for tropical climates.”

The process of cloud seeding is as follows. Experts observe the clouds on radar (located in JNTU — IST section) and check whether they have sufficient water.
The seeding material is then taken on a plane, with experts directing the pilot regarding the exact latitude and longitude of the cloud. The pilot spray the material into the cloud. The water vapour in the cloud will coalesce around the CCN and become bigger droplets, falling as rain.

After seeding, it takes 30 minutes to two hours to rain. However, the place over which the cloud was seeding will not receive rain as the cloud would have moved 10-12 km by then. In tropical countries, calcium chloride is used while it is silver iodide for cooler climes.

“Cloud seeding causes no harm to nature. It just enhances rainfall. It is most important for the state to consider this as groundwater needs to be recharged. The state cannot depend on just river water for agriculture,” Dr Subbarao added.
When contacted, managing director of HMWS&SB, Mr M. Dana Kishore said that they have no plans for cloud seeding yet.

In 2014, the TS government had instructed the irrigation department to consult experts from JNTU and implement cloud seeding. Officials say that no plan had been proposed yet.

The concept was  first introduced in the state in 2007 and a total of Rs 20 crore was spent on it each year.