The technique of inducing precipitation from certain types of clouds is a process called “Cloud Seeding”. A more sophisticated but seemingly generic expression is “Weather Modification”. Cloud seeding is defined as “ A process of treatment of cloud systems with the aim of enhancing precipitation”. The process was developed based on a chance discovery in a GE laboratory in the United States, sometime in the mid forties wherein it was found that when in contact with ice shavings, super-cooled water droplets froze and immediately turned into ice crystals. Although demonstrated for the first time in 1946 with a fixed wing aircraft spraying silver iodide in a cloud at 14000 ft, the concept became a practical reality only in 1950. Apart from enhancing rainfall, the process finds application for hail suppression, fog dispersal and weakening of tornados, all based on the basic principle of inducing precipitation.

For the purpose of cloud seeding, clouds are divided into two categories each requiring a different seeding method. A cloud where the temperature is below the freezing point i e 0 degrees Celsius, is categorized as Cold Cloud and the seeding process is called Cold Cloud Seeding. Where the temperature is above the freezing point, it is described as Warm Cloud and the seeding process is called Warm Cloud Seeding. Large cumulonimbus clouds can have warm regions at lower levels and cold regions in the upper reaches thus necessitating a combination of seeding methods.