Every time Chennai faces a stark water shortage and poor rainfall, talk emerges on cloud seeding to induce rainfall.
Residents of the southern suburbs recently have represented that cloud seeding may be done to mitigate the impact of a water crisis.
Cloud seeding is an artificial way of inducing moisture in the clouds to cause rainfall. Weather experts recall that the State government attempted cloud seeding initiative in 1975 after a poor Northeast monsoon in 1974. The Indian Institute of Tropical Meteorology, Pune, has done several experiments at the national level.
R.G. Subramanian, former radar meteorologist who was deputed to work with Chennai Metrowater between 1984-87 on cloud seeding, recalled how the experiment was carried over catchment areas of the city reservoirs then.
Type of clouds
“Only certain kind of clouds can be seeded and it needs to have enough nuclei to process cloud seeding and thunder cloud development. We took the help of a U.S. firm, Atmospheric Inc, California, who guided us with their pilots and aircraft. We used silver iodide particles in the form of candles and fitted them on to the wings of aircraft. These candles were burnt and released into cloud masses at an altitude above 20,000 feet,” he said.
Not unfailing
However, this cannot be done in dry weather conditions. “We can experiment cloud seeding only when the cloud is in a developing stage. We cannot quantify the volume of rainfall that the experiment will bring. Even then, we could not prove that the cloud seeding caused rains as these clouds could otherwise too had the possibility of developing on their own,” he said.
Mr. Subramanian recalled that there was a heavy downpour that lasted for over 10 days in November 1985. But, there was no means to relate to cloud seeding experiment then.
In May 2003, cloud seeding was attempted through aerial spraying of common salt instead of silver iodide. But, it failed as there were no rain-bearing clouds.
