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Seeding isn’t believing

No more experiments after last year’s failure, civic body decides not to try cloud seeding again. Instead, it says, it is looking at alternative sources such as borewells, ringwells and insisting on water recycling in new buildings, reports Rajendra Aklekar.

india Updated: Jun 07, 2010 00:24 IST
Rajendra Aklekar

You can’t create rain. That’s what the Brihanmumbai Municipal Corporation (BMC) learnt the hard way last year from its experiments with cloud seeding.

No wonder the BMC is wary of revisiting it this year. Officials said they would, instead, try and work out other means to ensure the city has enough water if the monsoon is delayed.

Last year’s deficient monsoon forced the BMC to cut water supply to homes by 15 per cent and to commercial establishments by 30 per cent.

“Cloud seeding did not work last year; there’s no point repeating the experiment. If it doesn’t rain on time, we will meet with the state government and work out a solution. We will look at all the alternatives,” said Rahul Shewale, chairman of the BMC’s Standing Committee.

“There will be no cloud seeding this year,” confirmed Additional Municipal Commissioner Anil Diggikar.

Cloud seeding is a method of inducing precipitation from clouds using silver iodide or dry ice. Last year, it was tried out over the Tansa and Modak Sagar lakes. From a rented aircraft, sodium iodide was sprinkled over the clouds to induce rainfall.

What are the solutions the BMC is looking at? Officials said they have discontinued water supply to civic gardens and more than 300 public toilets since May 1.

A number of public utilities are being provided water through alternative sources like ringwells and borewells.

Borewells require hand pumps to draw water, while ringwells are small 1 mt x 1 mt wells used to draw water for non-potable purposes.

So far, the BMC has received proposals for 485 borewells, of which work on 71 has begun. Most of them are in the western suburbs and the island city. The BMC is digging 300 ringwells itself — 100 each in the island city, eastern suburbs and western suburbs at a cost of Rs 41 crore.

Additionally, under the green building policy that is being drafted, it will become mandatory for new buildings to have water recycling plants.

The BMC will give a 20 per cent rebate on property tax to buildings that comply.

The water situation in Mumbai this year is worrying — supply from four of its six lakes has been discontinued because of dipping water levels. Only 2,900 million litres a day (MLD) are being supplied; the normal supply is 3,400 MLD.

Cloud seeding

It involves the spreading of silver iodide aerosols or dry ice on clouds to stimulate precipitation. Most rainfall starts through the growth of ice crystals from super-cooled cloud droplets (droplets colder than the freezing point) in the upper parts of clouds. The silver iodide encourages the growth of new ice particles. Silver iodide flares are ignited and dispersed as an aircraft flies through the cloud at a height of 18,000 ft to 35,000 ft.

When Mumbai tried it

The BMC allotted two clouding seeding contracts in 2009 — one to Shantilal Meckoni of Meckoni Enterprises and the other to Bangalore-based Agni Aviation. Agni was awarded the Rs 8-crore contract to carry out the aerial experiment for 60 days, while Meckoni was paid Rs 15 lakh for conventional cloud seeding.

Success in 1992

On July 23, 1992, 10 cloud seeding stations were set up in a three-kilometre radius of the Tansa and Upper Vaitarna lakes. In half an hour, iodide fumes from the generators reached the clouds and it rained within an hour.