Why artificial rain is not a solution to drought

The technique of cloud seeding to produce artificial rain is only effective when there are clouds that are already on the verge of producing precipitation. Boris Roessler / Keystone

Dozens of countries are investing millions to artificially increase precipitation in arid regions. However, the idea of tackling drought with “on-demand” rain is a fantasy, according to a cloud-seeding expert in Switzerland.

A guaranteed view of the Matterhorn, 365 days a year: that is the promise the tourism director of Zermatt made this year. According to Daniel Luggen, the Swiss Alpine village will become the world’s first destination capable of ensuring that its iconic landmark is always visible, thanks to technology capable of dispersing clouds.

This is an enticing prospect for the thousands of people who visit the famous mountain every year. The only problem is … it’s not true. The promise, which was shared on social mediaExternal link, was an April Fool’s joke.

However, there is a grain of truth behind the concept. It is indeed possible to modify the structure of clouds by releasing chemical substances into the atmosphere. The technique is used not only to disperse clouds, but also to reduce air pollution and, above all, to prevent hail damage and enhance rainfall and snowfall.

So-called cloud seeding has been practised for nearly a century, and Switzerland was among the countries pioneering the technology. Now, with droughts intensifying due to climate changeExternal link and a decline in usable freshwater in many regions, interest in manipulating weather conditions has grown.

In 2025, drought affected nearly a third of the Earth’s land surface, and this year could be the hottest ever recorded. Since the early 2000s, many regions of Europe, including Switzerland, have become drier.

>> This video explains how clouds form and the role of cloud seeding in triggering rain:

‘Waste of resources’

According to the World Meteorological Organization (WMO), around 50 countries – including the United States, China and Iran – are experimenting with cloud seeding.

The WMO describes it as “a sustainable source of freshwater”. Companies such as US-based Rainmaker, one of the sector’s leading players, claim they can put an end to water scarcity with cloud-seeding technologies.

So, have we entered the era of rain on demand? “Absolutely not,” says Ulrike Lohmann, a professor of atmospheric physics at federal technology institute ETH Zurich and a leading expert in cloud research. She is currently conducting cloud-seeding experiments in SwitzerlandExternal link to study the processes that occur within clouds.

“Many countries invest in artificial rain because they are desperate: they need more precipitation as soils become increasingly arid,” she says. The results, however, are limited. “The amount of water obtained through cloud seeding is so small that these interventions amount to a waste of resources,” Lohmann adds.

>> Despite its countless rivers, lakes and glaciers, Switzerland is not immune to drought:

How is artificial rain produced?

Cloud seeding involves the injection of particles into clouds. These particles act as condensation nuclei around which tiny water droplets or ice crystals suspended in the air cluster. When these clusters become large and heavy enough, they fall as rain or, depending on temperature, snow.

The particles can be dispersed by aircraft or drones, or by special rockets launched from the ground. Silver iodide is the most commonly used substance because it has a structure similar to ice. Potassium iodide, dry ice, sodium chloride and biological materials such as pollen or bacteria are also used.

Silver iodide is not considered problematic in the relatively small quantities (ranging from tens of grams to a few kilograms) used in cloud seeding, Lohmann explains. This substance is naturally present in soils. However, prolonged use in the same area could have negative effects on the environment or human health.

Staff at the local meteorological office in Shijiazhuang, in Hebei province, China, launch rockets for cloud seeding in order to induce rainfall in May 2021. Zhang Haiqiang / Getty Images

Few clouds can produce artificial rain

Cloud seeding requires already existing clouds, and the technique cannot generate precipitation from nothing, Lohmann says. “We can alter the microstructure of a cloud and modify the balance between water droplets and ice crystals within it. But we are unable to change the weather conditions that lead to its formation.”

For example, creating artificial rain in the often-cloudless desert to make it greener is “nonsense,” the expert emphasises.

Most clouds – the WMO distinguishes ten typesExternal link based on shape and altitude – do not produce precipitation and are often too thin to do so. “Very few clouds are truly susceptible to cloud seeding,” Lohmann says.

The clouds that do produce precipitation are cumulonimbus, the classic vertically developed storm cloud, and nimbostratus, a low, horizontally developed cloud with a dark grey colour. “We can only intervene in clouds that are already on the verge of producing rain.”

Reported success

When clouds are present, some nations have found success in inducing them to drop rain. China operates the world’s largest weather modification programme. Since 2014, it has carried out more than 27,000 cloud-seeding operationsExternal link, investing over $2 billionExternal link (CHF1.6 billion).

By the end of 2025, the Chinese meteorological agency reported that its artificial rain and snow operations had produced 168 billion tonnes of additional precipitationExternal link since 2021. This volume of water could fill around 67 million Olympic-sized swimming pools.

According to a recent Chinese studyExternal link, precipitation and vegetation cover in the Shiyang River basin, in the country’s northwest, have increased significantly since cloud seeding began there in 2010. However, some experts question these results.

Other countries – including the United States, India, Pakistan, Iran, the United Arab Emirates, Saudi Arabia, Russia, Thailand and Australia – have also experimented with or adopted cloud-seeding techniques in efforts to combat drought. Recently, Indian authorities used artificial rain to reduce air pollution in New Delhi.

Cloud seeding to prevent hail damage

Cloud-seeding programmes also exist in Europe, although they are less extensive than in Asia and the Middle East. In countries such as France and Spain, the goal is to reduce damage caused by hail. Injecting particles into clouds promotes the formation of many small hailstones, which are less destructive than fewer large ones.

Switzerland was one of the first countries to use this technique against hail. The first tests date back to the 1950s. However, the experiments – including more recent ones conducted by the insurance company BaloiseExternal link – have been discontinued because they were deemed ineffective.

Buildings damaged by hail in Losone, Switzerland, in August 2023. Keystone / Ti-Press / Samuel Golay

Would it have rained anyway?

Cloud seeding to induce artificial rain or snow does work, says Ulrike Lohmann. “But not to an extent that generates truly significant precipitation.” The amount of rainfall depends on the water content of the cloud – “a factor we cannot influence”.

In the case of experiments in China, the total area involved is so vast – around five million square kilometresExternal link, roughly half the country – that, at a local scale, the additional millimetres of rainfall are almost negligible, she explains.

There is another limitation: it is not possible to determine with certainty whether a given rainfall event is actually due to cloud seeding or would have occurred anyway. “We do not have scientific data that can prove this, also because no two clouds are identical for comparison.”

“Cloud seeding is not a solution to drought,” Lohmann stresses. The only aspect it can influence is the timing of precipitation: it may rain a bit earlier or a bit later.

Tensions between states over water

Lohmann sees more risks than benefits in seeding clouds to produce artificial rain. Although costs are lower than those associated with large-scale climate interventions (climate geoengineering), they still become high when applied over vast areas. Large fleets of aircraft or drones would be required, involving investments of millions of dollars, she says.

Seeding a cloud to release water in a specific area could also reduce precipitation elsewhere. This could create tensions between regions or countries and lead to competition for water, Lohmann warns. “The amount of water in a cloud is limited: making it rain here means ‘taking’ water away from those further along its path.”

She says the few successful examples of cloud seeding relate to fighting pollution and clearing the sky. Lohmann cites the case of China, which artificially dispersed clouds to ensure clear skies during the opening ceremony of the 2008 Beijing Olympics.

“Cloud seeding is more effective at thinning clouds and clearing the sky than at producing artificial rain,” she says.

That’s good news for Zermatt’s tourism office – in case it does ever decide to guarantee clear skies around the Matterhorn.

Edited by Gabe Bullard/vdv/ts