The Ministry of Earth Sciences’ ongoing Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) is proving to be a welcome method for mitigating extreme drought conditions. It will also pave the way for a new cloud seeding protocol that can be followed in keeping with Indian conditions in future.
Cloud seeding is a method of enabling inefficient clouds to bring rain, or enhance rainfall from a seedable cloud by introducing seeding material. The secondary effect of evaporation from falling precipitation improves the thermodynamic efficiency of the environment to form fresh convective clouds and more rain. This principle is used to enhance rainfall and reduce pollution. Two types of seeding—‘ground’, using generators and rockets, and, ‘aerial’ seeding using aircraft are possible. Based on the type of cloud to be seeded (warm or cold) to enhance precipitation or snow; hygroscopic seeding using salt as spray from the base of a cloud and cold cloud seeding using silver iodide as spray from the top of the cloud may be deployed.
Need for seeding
The increase in rainfall due to cloud seeding can depend on many factors such as cloud size, liquid water content of the cloud and prevailing atmospheric conditions. Seeding is done on individual cloud cells, and sometimes, on clusters of clouds. The availability of suitable clouds depends on weather conditions. If more suitable clouds are available, a lot more area is covered. Cloud seeding however, cannot mitigate drought conditions. But, timely rainfall produced through cloud seeding, even in small quantities can help the survival of crops in stressed conditions. Similarly, cloud seeding if carried out in a targeted manner over catchment areas have been found useful in increasing the water level in dams.
As cloud seeding involves increasing the efficiency of conversion of cloud water to raindrops within a cloud, it has no effect on adjacent clouds. Thus, there is no decrease in rainfall in the vicinity. Ground based and rocket methods for seeding warm clouds are not very effective as there is no guarantee that the particles produced will reach the updraft regions of the clouds.
This story is from the July-August 2016 edition of Geography and You.
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This story is from the July-August 2016 edition of Geography and You.
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Former Professor of Economics and Education, School of Social Sciences, Jawaharlal Nehru University, New Delhi. bkhadria@gmail.com.
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