Kelly McSweeney

Aug 14th 2020

Making it Rain: The Science of Weather Manipulation


Farmers have long wished they could control the rain, and now weather manipulation can do just that. Cloud seeding, the most common way to modify weather, involves shooting silver iodide or other chemicals into clouds to encourage precipitation. In other words, a silver bullet can make it rain.

This technique is not perfect, and it can’t solve chronic drought, but it’s relatively inexpensive and many communities around the world are desperate for water. Scientists use weather modification to enhance rainfall and increase water supplies, to disperse fog and to minimize hail during storms. Private companies and state-sponsored groups have even used cloud seeding to drop fresh snow on ski mountains and to squeeze out the rain before major events such as the 2008 Beijing Olympics.

What is Cloud Seeding?

The idea is not to create clouds out of thin air, but to squeeze every last drop of rain from naturally occurring clouds. So, what is cloud seeding?

Cloud seeding adds substances to clouds by shooting them from the ground or dropping them from planes. Air already contains water vapor, but cloud seeding can encourage the water to condense until it falls from the sky. Normally, when air rises into the atmosphere, it cools and forms particles called ice nuclei, which clump together to form clouds. When enough of these cloud droplets combine, they grow bigger until they are heavy enough that they fall to the ground in some form of precipitation, determined by the temperature and other conditions. Adding a “seed” gives clouds a boost by creating ice nuclei that grow faster and bigger than normal.

Glaciogenic seeding is a technique for squeezing water from cold clouds. Back in 1946, Bernard Vonnegut (author Kurt’s brother) was one of the researchers at General Electric who discovered that silver iodide could help clouds form ice crystals. Scientists still aren’t exactly sure how it works, but it’s possible that ice easily bonds with silver iodide because they both have similar structures at the molecular level. When more particles collide, ice crystals are formed, and soon the cloud is full of heavy water droplets that become rain. Similarly, hygroscopic seeding is a technique for warm clouds, wherein a simple salt helps encourage water droplets to collide and produce rain.

Other weather manipulation techniques that have been considered over the years include: blowing storms away from land with windmills, cooling the ocean with cryogenic material or icebergs, delaying surface evaporation with monomolecular films, blowing a hurricane apart with hydrogen bombs or laser beams and injecting air into the center of a storm. Cloud seeding has prevailed because it is the simplest and most cost-effective way to change the weather.

Who is Manipulating the Weather?

Although weather manipulation lingers on the fringes of the scientific community, it is practiced more widely than one might expect. More than 50 countries around the world currently have weather modification programs and the World Meteorological Organization just hosted an expert team meeting on weather modification in Geneva in June 2017.

The reasons for modifying weather vary, depending on where the operation takes place. Russia has removed cloud cover for a national holiday, while India has focused on encouraging rain to fall in drought conditions.

China made headlines when authorities said they had cleared the skies by shooting salt-filled bullets into clouds ahead of the 2008 Beijing Olympics. Then, in 2016, the Chinese government announced it had allocated 199 million yuan ($29.76 million) to spend on its weather modification program to combat drought and reduce the impact of natural disasters.

In 2015 the United Arab Emirates (UAE) launched a $5-million research program for “rain enhancement science.” Groundwater supplies were running low and demand for water is projected to double in the next 15 years as the country continues to grow. In 2016, the UAE carried out 177 cloud seeding operations — primarily hygroscopic seeding in the mountains to add water to aquifers and reservoirs.

The United States is no stranger to weather manipulation, either. From the mid-1960s through the early 1980s, NOAA (National Oceanic and Atmospheric Administration) actively pursued Project STORMFURY, a program for experimental hurricane modification. Cloud seeding has especially been used in the Great Plains and western states to combat drought.

Wyoming just completed a $15-million study over 10 years that concluded that cloud seeding can add, on average, 10 percent more snow to an existing storm. In Idaho this year, the National Science Foundation partially funded a research project to test seeding clouds to increase snowfall near communities where it can be used for crop irrigation and hydropower.

“Idaho Power is interested in putting more snow on the ground in the mountains, which leads to more water in rivers from snowmelt,” said atmospheric scientist Jeff French of the University of Wyoming, in a statement. “In turn, that leads to more power generation capability throughout the year.”

Weighing the Costs and Benefits

Messing with the weather is a tricky science, and more research is needed to explain exactly how it works. There has been healthy skepticism that challenges whether cloud seeding and other techniques are effective. Since weather systems are complex and impossible to duplicate, it’s hard to prove how much rain has been added to a cloud.

Aside from proving the efficacy, there are also risks involved with modifying nature. Introducing salt or other chemicals into the rain could alter microclimates and possibly interfere with nearby crop growth, which would defeat the whole purpose. There is also a potential to abuse the science by using it as a military tactic to force storms on enemies or sabotage crops, though this practice is banned by the United Nations.

Nevertheless, weather manipulation is worth exploring, since when used properly it has so much potential to work for the greater good. It can reduce fog at airports, minimize air pollution in large cities and be used for hydropower. It is mostly used to add water to areas with chronic drought, and even a small percentage increase could go a long way toward creating better agricultural conditions.

It can also prevent or reduce damaging weather, such as hail, hurricanes and tornadoes. In the Canadian province of Alberta, in 2012, scientists attempted to use cloud seeding to mitigate a hail storm. They hypothesized that seeding the clouds would redistribute the water vapor in the clouds to form smaller hailstones rather than the golf ball-sized hail that was predicted. Radar data collected afterward showed that the storm was 27 percent milder than the original forecast. It’s hard to prove cause and effect, but meteorologists involved in the project say it saved up to CAD$100 million in property damage. In places that are prone to severe storms, even a slight reduction in hail intensity could save millions and easily offset the cost of a weather manipulation program.

Cloud seeding is still an imperfect science with room for progress, but one with potential to positively alter the way weather affects our lives.