Playing God: How cloud seeding works

After the UAE's record month of rainfall, understanding cloud seeding has become pretty important.

Neil Churchill April 18, 2016

The first I heard about cloud seeding was during the 2008 Beijing Olympics, when China proudly claimed they had done the complete opposite and kept the skies clear for the entirety of the games.

Since then, playing God by way of rainfall has become extremely popular. Just this week, a local meteorologist, Sufian Farrah, claimed cloud seeding was behind the UAE’s record rainfall last month, when a downpour on March 9 of 287 millimetres measured higher than the predicted annual rainfall. The result? Schools were shut, flights were delayed and buildings were damaged.

But creating artificial rain could have huge economic benefits in parts of the world where natural precipitation is rare – the GCC with its expansive deserts is a prime example. While the desert may be unforgivingly dry and hot, it actually only takes a small amount of rainfall to facilitate plant growth and help the ecosystem to flourish. 

So how does it work?

To understand how cloud seeding works, it’s worth briefly remembering how natural rain occurs. When supercooled water droplets reach a temperature below zero centrigrade they turn into ice crystals. Being too heavy to remain suspended in the air, these crystals fall to earth, melting along the way before voila, they hit the ground as rain. A rainstorm happens when this process is multiplied.

All that cloud seeding does is to help this process along. The ‘seeds’ that are used – silver iodine or calcium chloride, which are sprayed from a plane or from a cannon device on the ground – provide extra nuclei that force the natural water in the skies to condense and crystallise. Even in dry areas, a UAE desert for example, the air still contains water droplets. 

So the process is not creating rain from nothing, it’s more giving a helping hand to rain that otherwise wouldn’t be able to materialise.

But does it work?

Well, if Farrah, meteorologist at the National Centre for Meteorology and Seismology, is right, then last month the UAE was proof that it certainly does work.

But some studies have claimed it’s hard to know for sure. After all, it’s impossible to carry out a controlled experiment in the open atmosphere. It may have been that the UAE was scheduled for the deluge last month anyway, or that cloud seeding only played a small role. 

The UAE has been using cloud seeding for quite some time though. Back in 2010, Abu Dhabi’s deserts experienced no fewer than 52 storms, in July and August no less. Local scientists claimed the downpours were artificial and part of an $11 million experiment. Lampshade-shaped ionizers in the desert were believed to shoot the seeds into the sky. According to TIME, on the 52 days that it rained, forecasters did not predict rainfall once.

The risks

While playing God has long been an obsession for man, there are risks that cloud seeding can bring. While China proudly told the world it had mastered the opposite feat in 2008, it was apparently still learning the ropes just a year later.

After deciding to seed clouds in November 2009, scientists failed to see a sudden incoming cold snap, resulting in the artificial rain falling as snow. It was the earliest snow seen in Beijing for ten years.

But despite those risks, it’s hard to argue against the benefits of being able to produce precipitation in areas were rainfall is rare and much needed. Just don’t be surprised in the future if it snows in the desert. 

Images: Alamy, pujadutta