Sunday Times 2
Do we need artificial rain in March?
According to media reports, Thai experts launched a cloud seeding programme recently to produce artificial rain in Sri Lanka and the practical part of the project will take place this month.
Most Sri Lankans, including schoolchildren and teachers, may question the need to produce artificial rain in March because the first inter-monsoon season sets in by mid-March every year. Another important fact is that as a result of heavy rains in the latter part of second inter-monsoon season and the early part of the Northeast Monsoon last year, almost all the catchment reservoirs are still full. It is a known fact that convective rains during the first inter-monsoon (FIM) period in March-April bring a significant amount of precipitation in many areas of the country.
As we learn in school, one part of the water cycle is the precipitation of water drops to the ground from clouds. The whole process of rain depends on a series of physical changes in the lower atmosphere. Moist air rises up and becomes saturated with moisture due to cooling at atmospheric levels above about 500 metres; the saturated moisture then condenses to form water droplets; the tiny droplets combine to form large water drops and ultimately fall down as rain, thus completing the process. This natural process is supported and accelerated by a number of atmospheric parameters when requirements are naturally fulfilled.
Then…..what is the meaning of artificial rain making?
With the development of scientific and technological applications, we could observe all atmospheric parameters and physical processes even at very high atmospheric levels. A number of experiments were launched with the hope of accelerating some steps in producing rain artificially by using chemicals and some materials. A peep into history will inform us that in 1946, scientists in Vonnegut in the United States found out that silver iodide particles, acting as ice nuclei, were capable of forming ice crystals out of water droplets at a temperature of 4 degrees Celsius below zero.
In the same year, US scientist Vincent Schaefer discovered that dry ice (solid carbon dioxide), which exists at 70 degrees Celsius below zero, when crushed and scattered in a cloud of super-cooled water droplets, produces ice particles which multiply very rapidly in numbers. Field experiments conducted by Langnluir and Schaefer showed that these techniques were reasonably successful in producing some degree of precipitation from ordinarily non-precipitating cumulus clouds. Several techniques have been used in the ‘seeding’ of ice clouds. For instance, fine silver iodide particles — or dry ice — have been scattered from aircraft flying at cloud base, the reason being that the updrafts in the clouds tend to carry the seeding particles upwards and hence prolong their lifetime. In other experiments, silver iodide solutions and acetone were burned by ground-based burners and the smoke allowed to rise into selected clouds.
A number of countries launch cloud seeding processes to produce rain during prolonged droughts. As the clouds develop only in a high humid atmosphere and they tend to move with prevailing wind streams, upper air observations are performed before performing cloud seeding to verify whether the conditions are favourable for cloud seeding. This is because seeding cloud is an expensive exercise. It may be a successful exercise for countries with a significantly large geographical area but not for tiny land masses.
Sri Lankans may remember that a cloud seeding project was launched in the 1980s, disregarding concerns expressed by eminent scientists, including Prof. Osmand Jayarathna of the University of Colombo. It was merely a waste of funds with no successful outcome. Prof. Jayarathna had a presentation at the annual sessions of the Sri Lanka Association for the Advancement of Science (SLAAS) to make the public aware about the worst negative results of the artificial rain-making experiment.
Without considering all these facts, someone or a group seem to have planned to make artificial rain in Sri Lanka in a few days to come. As the Meteorological Department forecasts, north east monsoon rains will occur in several parts of the island. Also the inter monsoon conditions will prevail over the island, with the northward equinox of the Sun in March. With all of these natural atmospheric conditions, we have to ask from the authorities concerned, “Do we need artificial rain in March?”
(The writer is a visiting lecturer at the Post-Graduate Institute of Science (PGIS), University of Peradeniya and was a director of Meteorology)