New Delhi: Amid disappointing forecasts for rainfall in the June-September monsoon, the government is working on bringing rain through another method—cloud seeding—that senior scientists say is set to become an important part of India’s weather management.
The method involves trying to modify the weather by changing the amount of precipitation—any product of the condensation of atmospheric water vapour that falls under gravity—in clouds to either increase or decrease rainfall.
This is done by dispensing cloud seeds—known scientifically as cloud condensation nuclei (CCN)—at the base of clouds from a special seeder aircraft. The cloud seeds help turn water vapour into its liquid state—a process known as condensation—and thus create rainfall.
Conversely, the clouds can be blasted with large water-
absorbing particles such as salt to decrease rainfall.
The twin technologies are useful because India, unlike many other countries, often has to deal with both drought and flood conditions in different parts of the country.
The Indian Institute of Tropical Meteorology (IITM), a part of the ministry of earth sciences, has launched the third and latest phase of an experiment that began in 2003. The first part of the current phase, spanning 2014 and 2015, will be conducted from Varanasi, which will be the base station for the central Indian region, the focus of the experiment.
To be sure this is not the first time the government is attempting cloud seeding—it has been tried in various states with varying degrees of success. This year’s experiment is, however, significant in the context of the sub-par monsoon forecast. Central India is likely to be one of the regions that will see deficient rains.
This year’s experiment will focus on investigating how aerosols, which are minute particles suspended in the atmosphere, can lead to strengthening of clouds and help develop a basis for direct observations on the characteristics that determine rainy and dry monsoon conditions.
“Ground-based observations have already begun in the Varanasi station, and will continue till the end of monsoon,” said Thara Prabhakaran, a senior scientist at IITM, which has been conducting cloud seeding experiments since the 1970s.
The current IITM experiment is called the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX), which aims to investigate the interaction between aerosol and cloud precipitation in various parts of India and to carry out cloud seeding over Varanasi in central India.
In 2003, when the first cloud-seeding operations were carried out in Andhra Pradesh, no change was detected in rainfall. But after the first phase of CAIPEEX was carried out in 2009, also in Andhra Pradesh, more than 17% of rainfall in the 12 districts was attributed to cloud seeding.
The second phase was carried out from 2010 to 2011, when the main focus was to collect more samples of clouds that were seeded.
“Since the experiment started late in the monsoon season due to delay in the hurdles of permission of import of an instrumented aircraft, the samples collected were not enough to make a statistically significant conclusion on the experiment,” said IITM’s Prabhakaran.
The second part of the current third phase will span 2015 and 2016, when scientists will focus on collecting more seeding samples with a so-called instrumented aircraft—a special plane, imported from the US in this case, consisting of at least 25 instruments that can measure atmospheric properties, observe water droplets and probe aerosols.
“Cloud-seeding operations will take place in June-July in Varanasi to carry experiments to see the interaction between clouds and aerosol. Weather modification operations are really going to gain importance in the coming years,” said M. Rajeevan, a senior scientist and adviser in the ministry of earth sciences.
“But it is difficult to modify nature, the practicalities are difficult. In some cases it may work, in most it doesn’t,” Rajeevan added.
In 2008, China attracted global attention when it cleared away rain clouds just before the opening ceremony of the Olympic Games. Other countries such as Russia, the US and South Africa, too, have been conducting such experiments with varying degrees of success.
This year, the Municipal Corporation of Greater Mumbai has approached IITM to ask if it could help bring artificial rain in certain areas of Mumbai.
“We’re conducting research on clouds and how they develop, and the role of aerosol in precipitation. IITM has no infrastructure, we can only give technical guidance. So far BMC (Brihanmumbai Municipal Corporation) had sent a request; we will provide technical guidance,” said B.N. Goswami, director, IITM.