A century after its first experiments, Switzerland still cannot tame hail

Around 6,000 cannon shots in one summer show how seriously Swiss communities once took the threat from the sky. In 1901, anti-hail systems were widespread across the country. A year earlier, in Collina d’Oro, Ticino, about ten large metal-cone cannons had been aimed at a storm front. Their shock waves were supposed to disrupt clouds before they reached the village.

The equipment has changed. The uncertainty has endured. Switzerland helped pioneer cloud seeding, a form of weather modification that releases particles into clouds from rockets, aircraft or ground-based systems. Yet a century of trials has not established that these interventions reliably prevent hail damage.

The issue is gaining practical importance. Summer hail already causes millions of francs in damage in Switzerland, affecting crops, buildings and vehicles. Climate change adds pressure by warming the atmosphere and strengthening the updrafts inside severe storms. Those rising currents can keep ice particles aloft longer, allowing larger hailstones to form.

The country’s search for a technical fix now sits between established atmospheric science and an expensive gamble. Researchers, farmers and insurers have reason to keep investigating. They also have a long record of results that remain difficult to interpret.

The first federal trial ran from 1948 to 1952. It formed part of a wider effort to replace local anti-hail practices with controlled experiments. The agriculture division of the Federal Department of Economics created a federal commission to study how hail forms and to finance research into ways of stopping it.

The commission organised four large-scale experiments, known as Grossversuch. The early work focused on rockets and other methods intended to counter hail formation. Later Swiss trials, including research carried out between the 1950s and 1980s, expanded the country’s knowledge of hail-producing storms. The experiments also exposed the difficulty of measuring success in a naturally chaotic environment.

A hailstorm does not arrive under laboratory conditions. Storm cells vary in size, movement and internal structure. Damage can be severe in one valley and limited a few kilometres away. A trial must establish what would have happened without intervention, while accounting for wind, temperature, moisture and the storm’s changing path.

That evidence has never reached a decisive conclusion. Marco Gaia of MeteoSwiss says the tested methods have not been shown conclusively to work. The finding does not erase the value of the research. It sets a clear boundary around what Switzerland can currently claim.

Silver iodide is intended to multiply ice particles inside a storm. In the standard cloud-seeding theory described by Swiss researchers, rockets or aircraft release particles into suitable clouds. Silver iodide can act as an ice-forming nucleus, encouraging supercooled water to freeze. The objective is to create many smaller hailstones rather than fewer large ones.

The proposed benefit is straightforward: smaller stones are more likely to melt or fall with less destructive force before reaching the ground. Reaching that result in a live thunderstorm is considerably harder. The seeding material must enter the right part of the cloud at the right moment, while the storm’s powerful updrafts and turbulent circulation continue to evolve.

A successful intervention would also need to be distinguished from ordinary variation. Some storms weaken, turn or miss populated areas without human assistance. Other storms produce hail in one location while rain falls nearby. Those patterns make before-and-after comparisons unreliable unless experiments are large, carefully controlled and repeated.

The Swiss record therefore supports a cautious description of cloud seeding. It is a plausible physical intervention under specific conditions. It is not a reliably proven shield for Swiss homes, vineyards or fields.

A 1977 rocket trial in Romoos brought the experiment into public view. Researchers from ETH Zurich tested Russian-made “Oblako” rockets in the Lucerne region on June 23 that year. Black-and-white photographs show two men loading a rocket into a launcher as storm research moved from laboratory theory into the Swiss landscape.

The scene captures the practical scale of the intervention. Anti-hail rockets were fired from the ground toward storm clouds, carrying substances intended to alter the formation of hail. Such operations required trained crews, suitable launch sites and a storm that could be identified and reached in time.

Switzerland’s mountainous geography makes the task especially demanding. Valleys and ridges channel weather, while storms can develop and shift rapidly across cantonal boundaries. A technique that appears promising in one storm may have little relevance to another with different moisture, temperature or wind conditions.

The Romoos work belongs to the broader series of Swiss experiments conducted from the 1950s through the 1980s. Those trials advanced knowledge, yet they did not settle the practical question of damage reduction. The rockets could reach the cloud. Researchers still struggled to prove what the cloud would have done without them.

Climate change is raising the cost of uncertainty. Switzerland’s hail problem is tied to the behaviour of severe thunderstorms, and a warmer atmosphere can support stronger updrafts that produce larger hailstones. The result is greater exposure for farms, homes, cars and other property when storms cross the country.

That pressure helps explain why cloud seeding remains part of the conversation despite its unresolved record. Insurance companies and scientists continue to look for ways to reduce losses. The attraction is clear: if many small hailstones could replace a smaller number of large ones, even a partial reduction in damage would matter to Swiss communities.

The evidence requires discipline. Gaia’s assessment at MeteoSwiss leaves no basis for presenting rockets or silver iodide as a dependable national defence. Recent experiments have not delivered the desired results, according to the source report, and decades of earlier work have not produced conclusive proof.

For Switzerland, the near-term value of cloud seeding may lie as much in measurement as intervention. Better observations of storm structure, hail size and local damage can improve forecasts and risk planning. Weather modification may continue to attract investment, but any claim of protection must survive rigorous comparisons against storms that were never seeded.