Cloud Seeding: How to make it rain

Incredibly, simply by dispersing salts into the air, rain-bearing cumulus clouds are germinated

Image by Stefanie van Dijk from Pixabay

The ability to control the weather might seem like something from science fiction, but since the 1940s scientists have been altering the elements in the form of cloud seeding. As the name suggests, cloud seeding is the process by which ‘seeds’ – in the form of simple table salt or silver iodide – are released into the atmosphere to spawn cloud growth.

By their very nature, clouds form when evaporated water molecules condense around atmospheric dust and ice, known as a nucleus. As more water droplets collect around the nucleus, larger droplets collide and begin to form clouds. This natural seeding is what scientists have been able to replicate using aeroplane-bound flares and even ground-launched rockets. However, this process cannot create clouds out of thin air; there first needs to be some water vapour or juvenile clouds in the area so that the artificial seeds can encourage clouds to form.

But why would we want to make clouds in the first place? Rather than simply indulging in the science of ‘playing God’, cloud seeding can be a lifeline to areas around the world where rainfall is minimal. For example, one of the keenest countries to undertake cloud-seeding programmes is the United Arab Emirates (UAE). As one of the driest nations on Earth, the UAE’s arid environment only receives around 120 millimetres of rainfall each year. Cloud seeding programmes to encourage precipitation are therefore vital to assist in agricultural practices.

However, creating a downpour for the sake of watering plants is just one reason for cloud seeding. It is a solution for a variety of weather problems, from strategically inducing rainfall to make way for blue skies in the 2008 Beijing Olympics to preventing heavy hail storms that cause physical damage to crops.

Spreading the seeds

How can seasoning clouds with a little salt make them grow?

Image credit: © Future PLC/ Illustration by Adrian Mann

This article was originally published in How It Works issue 134

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