Can cloud seeding be the answer to India's growing problem of uneven rains?

In the summer monsoon months of 2018 and 2019, two aircraft went up over Solapur, in Maharashtra, on a mission that was one of a kind. They were part of a Rs 200 crore project — though no confirmation of this amount is available — to infuse the clouds with particles having an affinity for water vapour.

This was part of the Cloud Aerosol Interaction and Rainfall Enhancement Experiment (CAIPEEX), Phase IV, conducted over two years to test the feasibility and effectiveness of cloud seeding to create rain.

This, understandably, has generated interest over its potential to address the growing problem of uneven rains in India.

CAIPEEX IV, according to some scientists, was one of the largest experiments in cloud seeding attempted anywhere in the world.

A few months back, the Indian Institute of Tropical Meteorology (IITM), Pune, an autonomous institute under the Union Ministry of Earth Sciences, released the findings of the experiment that was also published as a paper in the journal Bulletin of the American Meteorological Society. The report says CAIPEEX IV showed rainfall could be enhanced by up to (approximately) 46±13 per cent at some locations and, on an average, approximately 18±2.6 per cent over a 100 square kilometre area over the rain shadow region of Solapur.

The latter was equivalent to almost 8.67 millimetres of additional rainfall. Over two years, scientists at the IITM evaluated samples of 276 clouds to test the effectiveness of cloud seeding. “All measurements were done using a wide network of state-of-the-art equipment such as automatic rain gauges, radars, radiometers, and aircraft,” the report said. It added that the results showed robust statistical significance above the 95 per cent confidence level.

The first phase of CAIPEEX began in 2009. The second phase was in 2010-11, the third in 2014-15, and then came the fourth phase in Solapur in 2017-19. The report said the first three phases consisted of research and studies on clouds and airborne observations of clouds and rain. Their outcomes helped scientists at the IITM to design cloud seeding experiments for the fourth phase. The outcome, the report concluded, showed that cloud seeding under suitable conditions could effectively enhance rainfall in a region.

Seeding a cloud

“Simply speaking, cloud seeding is done by spraying chemicals on the base of the clouds through an aircraft. The clouds are spotted using radars and once a cloud is identified, the pilots are informed and they immediately go to the base of the cloud and pump the chemicals,” says Madhavan Rajeevan, former secretary to the Ministry of Earth Sciences and a well-regarded expert on Indian monsoon. He was also one of the people behind the cloud seeding experiment in Solapur.

According to the IITM report, cloud seeding is a technique in which cloud-forming particles are used to increase rainfall. It can be done in two ways, hygroscopic and glaciogenic. In the first, seeding is done at the base of warm clouds, using seed particles with an affinity for water vapour. Glaciogenic seeding, on the other hand, is carried out in cold clouds by seeding near the top of the cloud, using silver iodide particles, which may form ice particles in the clouds.

IITM tried hygroscopic seeding in the 1970s. Subsequently, several states, such as Maharashtra and Karnataka, from time to time attempted creating rains artificially, but with limited success. During monsoon, hygroscopic seeding is more advantageous in enhancing rainfall and ensuring longevity of the clouds.

More than 56 countries practise cloud seeding to create rain. Some of them are Australia, China, Russia, Thailand, the United Arab Emirates, and the United States.

Cost vs benefit

The IITM analysis showed that the approximate cost of producing water through cloud seeding was around 18 paise a litre. A few years back, a study showed that the Bombay Municipal Corporation spent Rs 19.44 for every 1,000 litres of water it supplied to Mumbaikars, or Rs 0.019 per litre.

So, does that make creating water by cloud seeding a costly affair?

Rajeevan agrees that the process of cloud seeding is costly. It costs a lot of money to hire aircraft. However, when staring at drought-like conditions, the cost could be worth it.

 “See, when you identify a cloud and seed it with aerosols, it may or may not rain. Secondly, even if you don’t seed a cloud, it could still rain. Therefore, the question is how beneficial it is to make rain by seeding a cloud, which this experiment tries to answer,” says Rajeevan.

He explains that in cloud seeding, when aerosols are injected into the clouds, the already present rain droplets grow in size. Once they grow sufficiently big, they rain down due to gravity. “Therefore, practically cloud seeding can only happen in the monsoon months, as you need some amount of moisture in the clouds that can then be enhanced through seeding. Cloud seeding can’t happen in clear blue skies,” says Rajeevan. That is one reason why cloud seeding cannot be the right solution to bring down Delhi’s pollution in winter. Nor can cloud seeding mitigate large-scale droughts. What it can do, however, is bring rain to a village facing water scarcity. Earth Sciences Minister Kiren Rijiju has also said that cloud seeding will be used only in extreme circumstances. The IITM experiment laid down elaborate protocols for state governments and others for doing cloud seeding. It also said that currently most of the technology and equipment required for cloud seeding were imported. “The centre at IITM should facilitate the indigenisation of technologies for cloud seeding aligned with the Make in India vision of the Government of India,” the report added.

Easier alternative

Bharat Sharma, scientist emeritus of International Water Management Institute, says cloud seeding should be attempted only in extreme conditions in places like perennially water-deficit areas such as Telangana or Vidarbha. “A much simpler way would be to conserve rainwater, because we in India get 1,000-1,100 mm of rainfall in a year and we don’t need artificial rain except perhaps in extreme conditions,” he says.

Studies show that of India’s annual rainfall, 35-55 per cent is the run-off rate in different regions. “The environmental flow requirement is a minimum of 10 to 15 per cent, while the rest can be used by creating water infrastructure or artificial groundwater recharge,” Sharma said.

Himanshu Thakkar of the South Asia Network on Dams, Rivers and People says the priority should be groundwater recharge, as this is where water extraction comes, and groundwater is the primary source of water in India.