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Cloud Seeding: Rain or No Rain?

Cloud seeding is the technology of introducing artificial nuclei or “seeds” (silver iodide, salt, dry ice), into clouds from either the air or ground to increase the chances of rain. The popular belief is that cloud seeding is done only to bring rain in a particular place. But did you know that the same technique is used to disperse rain?

Russia started the practice in the 1990s and continues to use it even today. For instance, in 2005, Russian President Vladimir Putin ordered the Russian Air Force to prevent rains over Moscow just before their military parade. In May 2016, the Russian government tried cloud seeding on International Worker's Day to coax the rain clouds to rain elsewhere.

In 2008, China apparently fired a barrage of 1,110 rockets to ensure that the Beijing Olympics opening ceremony was rain-free. Rockets with silver iodide reagents were fired from 21 sites in Beijing to intercept any rain headed towards Beijing and to trigger premature showers.

But how does one seed a cloud and trigger a shower? For rain to occur, the moisture droplets in a cloud need a “seed” or a core particle that they can latch onto and form bigger drops (similar to fruit pulp that needs a hard seed to hold onto and grow). When these drops become heavy, they precipitate as rain or snow. Sometimes, there aren’t enough seeds for the raindrops to form. And that’s where cloud seeding comes in.

Normally cloud seeding is used to bring rain in rain-scarce areas—which the state government did in September 2017 in the drought-hit North Karnataka. This effort apparently brought 10 to 25 percent more rain. Similarly, United Arab Emirates, considered a leader in rain enhancement, claims to have witnessed an increase in rainfall of about 10–35 percent following cloud seeding. Currently, more than 50 countries are reportedly undertaking cloud seeding efforts world-wide.

But despite advanced weather modification research since its discovery in the 1940s, scientists are unable to assert even today whether cloud seeding truly brings rain because of the immeasurability of treated clouds and the highly variable dependency of rain on temperature, cloud composition, and other factors. Knowledge about crystallization of water in clouds and balance of evaporation and precipitation in the atmosphere too remains limited. Heavy investments in this technology, however, continue.