Seed of an idea, but it can’t replace monsoon

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How are clouds seeded?

Cloud-seeding chemicals can be dispersed in clouds either by fly-through aircraft or by ground-based dispersion devices that use rockets or guns to fire canisters into the sky. Seeding has been shown to work better on days that are cloudy but rainless, and with clouds that already have some moisture. In case of seeding by aircraft, the pilot fires sodium chloride flares to the base of the cloud, and silver iodide flares to the top. The chemical particles are the embryos for the formation of larger drops, which ultimately fall as rain. When fired by rockets, chemical ‘seeds’ are propelled by air currents.

How much rain, and over what area, can seeding produce?

That depends on several factors, including the dimensions and moisture content of the cloud, and prevailing atmospheric conditions. It is difficult to assess the amount of rain produced by seeding unless a dense network of automatic rain gauges is employed. Rain is generally seen to start approximately 30-40 minutes after seeding, and continue for an hour or two. Since seeding is carried out in individual cloud cells, the availability of suitable clouds is key to how much area the artificial rain can cover.

Can cloud seeding substitute for a bad monsoon?

In terms of the area it covers, the precipitation it brings, and the length of the time it lasts, there is no substitute for the Indian monsoon. But cloud seeding can produce good rain over smaller areas, and can supplement the natural phenomenon. Since timely rain, rather than a lot of it, is what is often more important for crops, seeding can help. It is now a fairly advanced science — even though more research is needed for a deeper understanding of cloud formations, so that more significant meteorological interventions can be made. Different types of clouds may exist over a region, and the same type of seeding may not be effective for all; sometimes seeding is effective only over certain areas.

What does cloud seeding cost?

It involves use of infrastructure such as aircraft, radar, balloons and measuring and communications equipment, and is not cheap. Some years ago, the union Ministry of Earth Sciences allocated about Rs 14 crore to study the possibility of cloud seeding on a large scale in the country. The report submitted by the nodal agency, Pune-based Indian Institute of Tropical Meteorology, was largely positive. A plan to procure an aircraft for cloud physics studies is under consideration.

Where has seeding been successful?

While it is practised around the world, doubts remain over the ability of seeding to modify international weather, with studies in the US and Israel casting doubts over the efficacy of the process. Even so, rainmaking experiments have shown increasingly better results since being first attempted in the 1940s. The biggest faith in cloud seeding has been shown by China, which believes it can make it rain on arid regions by firing silver iodide rockets. It also claimed to have used cloud seeding to clear the air during the Beijing Olympics. Thailand, Indonesia, the UAE, several countries in Europe, Australia and the US have all experimented with cloud seeding. In India, Tamil Nadu, Karnataka, Andhra Pradesh and Maharashtra have attempted to seed clouds since the 1980s. Some positive impact notwithstanding, results have generally been patchy.

What does Maharashtra intend to do?

The state has seen three straight years of drought, and Relief and Rehabilitation Minister Eknath Khadse said at the beginning of June that cloud seeding would be taken up, especially in Vidarbha and Marathwada, if the India Meteorological Department’s forcast of a poor monsoon appeared to be coming true. This week, with the unusual rain in June drying out, Ram Shinde, Minister of State for Agriculture, said a few companies had offered to seed clouds for free to test the situation. In an editorial in Saamna on Thursday, however, the Shiv Sena, a partner in the Maharashtra government, called for trying out other options too. “There is no reason to complain against the cloud seeding project, but the question is how much rainfall will this project actually generate?” the Sena said.

So, what is the status of the experiment?

Shinde, who spoke in Pune, said the government had finalised Aurangabad as the base for carrying out cloud seeding, which would be conducted in a 250 km radius. A final decision would be taken in the next 15 days, he said. The Maharashtra Cabinet has in principle approved Rs 10 crore for cloud seeding. Seeding was last planned in the state in 2004, with Baramati as its base. The Baramati centre was expected to cover the districts of Pune, Satara, Sangli, Osmanabad, Beed, Nasik, Ahmednagar and Aurangabad.

HOW CLOUD SEEDING WORKS:

* Particles of dust or salt that have the ability to absorb moisture from the air rise as ‘haze’ into clouds.

* These hygroscopic particles form ‘nuclei’ around which moisture builds, but no rain can occur unless they reach a certain size.

* An aircraft (or rocket from the ground) can fire flares of chemicals that act as aerosols — additional nuclei in the cloud.

* As the particles of moisture grow larger, it may rain. How much it rains depends on the kind of cloud, among other things .