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The Delhi government, in collaboration with the Indian Institute of Technology, Kanpur, attempted to induce artificial rain to reduce pollution in the national capital on October 28.
The two cloud seeding trials, which cost nearly Rs 60 lakh, involved a small aircraft flying over several areas of Delhi and releasing flares containing silver iodide and sodium chloride (common salt) particles into the atmosphere. The effort resulted in 0.3 mm of rain over Noida and Greater Noida — there simply wasn’t enough moisture in the clouds to induce showers over New Delhi.
The national capital is no stranger to cloud seeding trials. The first such experiment took place here as far back as in 1957. It was conducted by the Delhi-based National Physical Laboratory (NPL)’s Rain and Cloud Physics Research (RCPR) unit, set up to undertake extensive scientific studies on cloud physics and rainmaking.
Cloud seeding experiments began to be carried out around the world after American chemist Vincent Schaefer and his colleagues at General Electric in New York made the first snowstorm in a laboratory freezer in 1946.
The technique was implemented in India for the first time in 1951, when Tata firms tried to induce artificial rains over the Western Ghats by using ground-based silver iodide generators. A year later, S K Banerji, the first director-general of the Indian Meteorological Department (IMD), experimented with cloud seeding using salt and silver iodide through hydrogen-filled balloons released from the ground.
Subsequently, similar trials were conducted in Delhi and other parts of north India by the RCPR unit, which was established at the NPL in 1955 and later, in 1967, transferred to Pune’s Indian Institute of Tropical Meteorology, then known as Institute of Tropical Meteorology.
Former IMD Director-General R R Kelkar tells The Indian Express, “In the 1950s, the science of what used to be called precipitation enhancement was still new. Indian researchers carried out experiments to see if they could do what Schaefer and others had done aboard. However, these trials (including the 1957 trial) were not done for the purpose of research since scientific trust in the technique of cloud seeding was not strong.”
He adds, “These experiments were usually conducted to address the needs of someone. For instance, Karnataka would ask scientists to carry out the experiment to tackle drought or Andhra Pradesh would want it to provide more rain for its farmers.”
The first cloud seeding trial in Delhi took place during the monsoon months of 1957 — between June and September — because the technique usually works when there is at least 50% moisture in the cloud.
To induce artificial rain, salts like silver iodide and sodium chloride are dispersed in the atmosphere to provide additional nuclei, around which more cloud droplets can form.
Before carrying out the 1957 experiment, the RCPR unit’s scientists examined the relevant weather features over the region to ensure they were suitable for the trial. For example, they look at the natural concentration of hygroscopic nuclei — the tiny, airborne particles like dust and sea salt that attract water vapour, and are essential for the formation of clouds and precipitation — in the air.
“Before embarking on a plan of cloud seeding by dissemination of hygroscopic nuclei in cloud air, it would be logical to try to make an estimate to whether and, if so, how frequently the need for such artificial nucleation actually arises in the area in question,” states a 1961 paper, titled ‘Cloud seeding trials at Delhi during monsoon months, July to September (1957-59)’, by A K Roy, V Ramana Murthy, R C Srivastava, and L T Khemani in IMD’s journal, Mausam.
While cloud seeding is typically done using aircraft these days, in 1957, scientists used ground-based generators to disperse particles in the atmosphere. One reason for using this method was that it was much simpler and more cost effective than deploying an aircraft, according to the paper.
Stating that it is “not possible to create a cloud artificially”, IMD’s Kelkar says, “One can only make a cloud rain. To do so, you inject particles into a cloud and water droplets form on those particles. Now, you can either take these particles in an airplane and put them at a certain level of the cloud, or you could spray these particles upward with a lot of force from the ground, just like you spray water in a garden.”
For the 1957 experiment, two sprayers were deployed. These sprayers operated simultaneously for about three hours during midday to disperse a dilute solution of common salt.
According to the 1961 paper, the RCPR unit continued to carry out cloud seeding trials during the monsoon months of 1958 and 1959. Although it did rain on some occasions, the efficacy of these experiments could not be ascertained due to wide-ranging results in each year.
“A rigorous testing of the method followed… is not easy, because of lack of control over dispersal of seeds into clouds of (the) right type and at the right moment and of the difficulties, as are common to all rainmaking trials, of separating out effects of natural variations in rainfall from those caused by seeding,” the paper states.
The scientists involved in the 1957 experiment concluded that there was a need to conduct trials for a larger number of monsoon seasons.
The writer is Senior Correspondent, The Indian Express
