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Cloud seeding is a method used to introduce suitable sized cloud condensation nuclei or ice nuclei to kick start rain. Representational image: PTI.

Will cloud seeding be prospective answer to Chennai water woes?

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Recently, the Minister of Municipal Administration and Water Supply Department, Tamil Nadu SP Velumani revealed that the government is mulling cloud seeding, in the backdrop of the acute water crisis in the state.

Cloud seeding is a method used to introduce suitable sized cloud condensation nuclei or ice nuclei (particles on which cloud droplets or ice particles form) to kick start precipitation. The state has attempted the method a few times in the past but with little success.

Several factors determine success

Thara Prabhakaran, Project Director, Cloud Aerosol Interaction and Precipitation Enhancement Experiment / Physics and Dynamics of Tropical Clouds, Indian Institute of Tropical Meteorology, explains that there are several types of cloud seeding. However, their success depends on a number of factors, she says.

She said, “Several factors are there. Among that type of clouds and their liquid content, stage of their growth, environmental temperature, wind and relative humidity, type of seed material used, their hygroscopicity (the ability to attract the moisture content of the air by absorbing or releasing water vapour) and size matters the most. For a cloud seeding process, it has to be well-planned and executed and documented with necessary observations of rainfall both using a radar and rain gauges.”

Cloud seeding an option in India and abroad

While world over there are 53 countries carrying out cloud seeding of various types, India too has been experimenting with the same. But a quantitative demonstration using high-quality observations are needed and that is the focus of the IITM programme, observes Prabhakaran.

“The operational cloud seeding was conducted in different states and is considered a viable option to enhance rainfall. However, will cloud seeding indeed bring rainfall? Clouds may also rain naturally but how we can investigate seeded clouds to make it rain? Since it is an expensive proposition, we need to understand what types of clouds are viable for seeding to produce more rain. Additionally, what should be the environmental conditions and ambient aerosol properties so that a proper decisions on seeding strategy can be planned. Clouds are very chaotic and depict turbulent motions can indeed change its growth or decay.”

The IITM programme Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX), with research experiments began in 2009 and has gathered airborne observations of clouds, which has been helpful in formulating the present cloud seeding science experiment.

“This project is part of the Ministry of Earth Sciences (MoES) program to understand process in the tropical clouds. Indian Institute of Tropical Meteorology (IITM) carry out this scientific investigation of cloud seeding under CAIPEEX,” she added.

The experiment is expected to give scientific guidelines for rain enhancement and to make recommendations for such activities over the arid regions of Maharashtra. “The main goal of the observational campaign of 2018-19 is to provide high-quality observations of cloud and precipitation related processes in natural and seeded clouds over the rain shadow region,” she said.

Karnataka stands as an example

While Karnataka has attempted the method several times in the past, in 2017, there was 27.7 per cent enhancement in the rains. The state is set for its next round of experiment in July this year. Dr GS Srinivasa Reddy, director, Karnataka State Natural Disaster Monitoring Centre, says the success in 2017 has to be attributed to the systematic planning. He adds, “Karnataka is a state with dense network of rain gauges- all gram panchayats (6500 of them) have telemetric rain gauges. These help, when you have to do an evaluation.”

The committees are monitoring all aspects of drought on different parameters like moisture availability which will help to target the areas. “We have been looking at clouds density and their water bearing, apart from establishing radars — three of them in total,” he added.

After obtaining clearance for cloud seeding from the Centre, the networking with air traffic managers is also pivotal to the implementation of the method, he pointed out.

Reddy also says that the timing of the process holds the key. “Apart from an integrated and well coordinated work, planning well in advance is very important. To execute the task in July, we began planning in February, a good four months ahead of the date set for the implementation of the plan,” he said.

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