Rain delay

A beer company tries to keep Brazilian Carnival revellers dry

Cloud-seeding is not a foolproof method

THUNDERSTORMS OFTEN show up uninvited to Carnival in Brazil. The authorities in Rio de Janeiro used to share meteorological data with a group of spiritual mediums who claimed to have rain-dispelling powers. That ended with the election of an evangelical mayor in 2016.

This year’s attempt to sway the skies took place in São Paulo as part of a publicity stunt by the party’s official sponsor, Skol, a Brazilian beer brand. “The fun stops when it rains,” says Pedro Adamy, Skol’s marketing director. So do beer sales.

Enter a company called ModClima. A ModClima aeroplane painted with Skol’s logo spritzed water droplets into cumulus clouds to make rain fall before the clouds reached the city. According to a zippy YouTube video that has been viewed 12m times, “Giro na Chuva” (roughly, Reverse the Rain) is a “mission worthy of science fiction”.

Whether it’s science or fiction is up for debate. The use of cloud-seeding to increase rainfall dates back to the 1940s. But the United States government stopped funding it in the 1980s due to a lack of “scientific proof of the efficacy of intentional weather modification”, according to the National Research Council. A new paper based on experiments in Idaho found that seeding clouds with silver iodide increased snowfall on three occasions, but the authors say that more research is needed to figure out if it can reliably promote precipitation. Paulo Artaxo, a Brazilian physicist, says flatly that cloud-seeding is “useless”.

Still, governments and firms in many countries use the technology. The city of Beijing tried cloud-seeding to divert rain away from the Olympic games in 2008. São Paulo’s water company has signed million-dollar contracts with ModClima to induce rain over reservoirs, most recently during a drought in 2014-15. Although cloud-seeding normally uses a chemical such as silver iodide to provide a surface around which water or ice droplets form, ModClima says it has invented an “experimental” method that uses water alone. Droplets sprayed into clouds expand as they are lifted by air currents and collide with others, forming raindrops, the firm claims.

Carnival-goers cheered when the first two days were cloudy but dry. “Not all heroes wear capes,” one wrote on her retweet of Skol’s video. But at around 5pm on February 24th, the sky darkened and rain pelted down. Revellers at one block party left the Skol stands and flocked to a vendor selling plastic rain capes. “Only God can control the weather,” said the poncho man.■

This article appeared in the The Americas section of the print edition under the headline "Rain delay"