Coaxing the clouds

The history of weather modification has been stormy. From exploding balloons to strewing smelly chemical concoctions around dams, Roelof Bezuidenhout looks at how we came to the exact science of rainmaking.

- Roelof Bezuidenhout

The idea of inducing rainfall artifically was first considered seriously in the US in the 1800s.

In 1838, the Americans hatched a plan to end a devastating drought by setting fire to huge forests, hoping that the smoke would stimulate rain. The plan was rejected, but in around 1890, the Texas government experimented with exploding balloons to seed clouds.

In 1916, Charles Hatfield, with a generous donation from the mayor of San Diego in California, mixed a concoction of 24 chemicals that smelt of rotten cheese and strewed it around a large reservoir outside the city. A flood ensued a few days later, washing away roads and railways.

Whether it was his fault or not, Hatfield disappeared overnight.

SOUTH AFRICA

The first attempt at cloud seeding in South Africa was in 1922, when someone tossed a bag of ordinary table salt from a small aeroplane into a promising cloud. The result, unfortunately, is unknown.

However, in 2007, a South African weather research project received an international award. At the time, Dr Deon Terblanche of the Bethlehem weather research station claimed that weather modification was an effective way to supplement water supplies when suitable clouds were available.

Silver iodide or dry ice is spread into clouds from an aircraft. Ice crystals form and become heavy enough to fall to earth as raindrops. Terblanche said that treated storms delivered twice as much rain as untreated clouds.

His experiments showed that 75 treated storms in a 100km by 100km area increased rainfall by 10%. And there are many more storms than that on the Highveld. It does not work at the coast due to the low clouds and high salt content of the air.