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A poor monsoon has Karnataka turning once again to cloud seeding to tackle water scarcity. The state government has approved a Rs 28 crore programme that will involve around 200 flying hours spread over 60 days, beginning in September. The operation will be carried out across Karnataka’s four revenue divisions, with flights directed towards areas where weather conditions are suitable for cloud seeding.
Announcing the programme, Major Irrigation Minister N Cheluvarayaswamy said the exercise was being taken up to address the rainfall deficit and “pre-empt” a possible water crisis. He said September would be the most suitable period for cloud seeing because of the availability of dense clouds, and that the government was targeting a 30% success rate.
According to the Karnataka State Natural Disaster Monitoring Centre (KSNDMC), 178 taluks across 27 of the state’s 31 districts were facing deficient rainfall by the end of July.
Can cloud seeding make a significant difference to Karnataka’s water situation? And what does a “30% success rate” mean?
What is cloud seeding?
Clouds contain tiny water droplets or ice particles, but not every cloud produces rain.
Cloud seeding is an attempt to alter the microphysical processes inside an existing cloud so that these droplets or ice particles grow large enough to cause precipitation.
The process needs a cloud that is already capable of producing precipitation. It cannot manufacture a rain-bearing cloud from nothing.
The material used depends on the type of cloud and the seeding technique. In warm clouds, hygroscopic materials such as salts can be introduced to encourage tiny water droplets to collide and grow. In colder clouds, glaciogenic materials such as silver iodide, dry ice, and liquid propane, can encourage the formation of ice crystals.
The material can be dispersed from aircraft using specialised flares or other equipment.
Flights will be guided by real-time information on cloud density and atmospheric conditions, with radar and other meteorological data being used to identify suitable clouds. The flights will not follow a fixed route every day. Instead, they are expected to be dynamically directed towards areas where radar and atmospheric observations indicate that suitable clouds are present.
Why is Karnataka doing this now?
The immediate concern is the state's deficient monsoon and the possibility of water scarcity.
Minister Cheluvarayaswamy said the government had decided to undertake cloud seeding because weather forecasts indicated that the state may not get sustained monsoon activity. The objective, he said, was to secure uninterrupted water availability for people and livestock.
The programme is expected to run for 60 days, with around 200 flying hours. The Minister said September would provide the most optimal window because cloud cover is expected to be denser during this period, while cloud volume is likely to reduce significantly by October.
The government has also proposed separate committees to oversee the operation. A monitoring committee will handle policy and inter-departmental coordination, while a technical committee involving scientists and experts from institutions including Indian Institute of Science, Indian Institute of Technology, and Indian Meteorology Department will monitor meteorological parameters and radar data. A field operations committee will oversee the flights, dispersal protocols, and assessment of rainfall on the ground.
Has Karnataka tried cloud seeding before?
Karnataka has conducted cloud-seeding operations before, including the Varshadhare programme in 2017.
That programme ran from August to November 2017 and used both hygroscopic and glaciogenic seeding. It was designed using knowledge from the Indian Institute of Tropical Meteorology's Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX).
Researchers subsequently analysed the results using a high-resolution network of around 6,000 rain gauges across Karnataka.
A 2019 peer-reviewed study of the 2017 programme found an average rainfall increase of 27.9% above natural rainfall in its analysis of 618 cases. The researchers estimated that about 2.1 trillion litres, or 2.1 TMC (thousand million cubic feet), of additional water was made available through the programme.
But that number needs context. The study did not mean that cloud seeding produced 27.9% more rain everywhere in Karnataka. Rather, it found an average 27.9% increase in rainfall in the specific cloud-seeding cases that were analysed, compared with the rainfall expected naturally in those cases. The effect depended on whether the clouds had the atmospheric conditions required for seeding to work.
So, does cloud seeding actually work?
There is scientific evidence that it can enhance rainfall under the right conditions. But the effect is neither automatic nor uniform.
One of India's most important experiments was CAIPEEX, conducted by the Indian Institute of Tropical Meteorology under the Ministry of Earth Sciences.
The experiment studied clouds over the rain-shadow region around Solapur in Maharashtra and used radar, aircraft, and ground instruments to understand what happens inside clouds before and after seeding.
The final results found that rainfall at some locations was enhanced by about 46%, while the larger 100 sq km area downwind showed an average enhancement of around 18%.
The experiment identified specific conditions under which seeding was more likely to work, including sufficient cloud liquid water, adequate cloud depth, and favourable atmospheric conditions.
This is why the quality of the clouds matters as much as the aircraft carrying out the operation.
Why is the government expecting a 30% success rate?
Minister Cheluvarayaswamy said Karnataka's earlier cloud-seeding exercises had recorded an average success rate of 18–20%, while the government is now aiming for 30%.
But “30% success” should not be understood as meaning that rainfall across Karnataka will increase by 30%.
Scientific studies use different ways of measuring the effectiveness of cloud seeding. Some measure rainfall at individual rain gauges, while others compare seeded and unseeded clouds or calculate rainfall over a larger area.
A peer-reviewed study on Karnataka's 2017 Varshadhare programme estimated that it produced an average rainfall increase of 27.9% above natural rainfall in the cases it analysed. India's larger CAIPEEX experiment found rainfall enhancement of about 46% at selected locations, but the average enhancement over a larger 100 sq km downwind area was around 18%.
So when the government says it is targeting a 30% success rate, it means it hopes to get around 30% more rain from clouds that are suitable for seeding. This means clouds that already have enough moisture and the right atmospheric conditions to produce rain. It does not mean rainfall across Karnataka will increase by 30%. Whether this happens will depend on the number and quality of clouds available for seeding.
