How cloud seeding can make it rain or prevent extreme weather

Cloud seeding has been named by some media reports as a possible contributor to record-setting rain and flooding in Dubai in the United Arab Emirates. Here's a closer look at what cloud seeding is, how it's used and whether it could have made the flooding worse.

It's the process of making tiny drops of water vapour and ice crystals in clouds stick together into larger, heavier droplets or pellets that fall as rain or snow.

Often, this is done by spraying particles of salts such as silver iodide or table salt using special flares carried by airplanes or projectiles such as rockets, cannons or missiles. 

The U.A.E. has also used drones to zap clouds with electric charges for cloud seeding.

No. It's actually been around since the 1940s. It's been used in dozens of countries, including Canada. Despite that, interestingly, it was only recently that scientists have been able to prove it works by distinguishing between natural and induced rain or snow.

It's often used to fight droughts by inducing rain or snow, including by the U.A.E. to try to recharge its dwindling groundwater supplies. 

In the U.S., there have been efforts to use it to fight wildfires.

In Canada, it's often used to lessen the damage caused by hail, by getting moisture in the clouds to fall as rain or snow before it can build up into hail.

"The results of about 70 years of research into the effectiveness of cloud seeding are mixed," wrote atmospheric scientist William R. Cotton of Colorado State University in a 2022 article published in The Conversation. He added that it requires the right kinds of clouds with enough moisture, and the right temperature and wind conditions, and produces only small increases in precipitation. 

A recent study measured the snow from three cloud seeding events and calculated that they caused enough water to fill 282 Olympic-sized swimming pools to fall over an area of 80 by 80 kilometres — a tenth of a millimetre on average at any given spot.

"Regardless of the mixed evidence, many communities are counting on it to work," Cotton said.

The U.A.E. National Centre of Meteorology says cloud seeding can boost rainfall from a specific cloud by 25 per cent under optimal conditions, and the technology "plays a crucial role in the broader context of climate change mitigation and building climate resilience."

Hail suppression is also considered effective enough that insurance companies in Canada invest millions a year to seed clouds in Alberta.

According to The Associated Press, several reports quoted meteorologists at the National Centre for Meteorology as saying they flew six or seven cloud-seeding flights before the rains. Flight-tracking data analyzed by AP showed one aircraft affiliated with the U.A.E.'s cloud seeding efforts flew around the country on Monday.