Artificial rain or anti-hail cannons: Can the weather be manipulated?

The white trails left by airplanes have nothing to do with experiments that could have caused the catastrophic storm that left more than 200 people dead in Valencia, Spain, neither is there other out-of-control climate engineering that is causing torrential rains or droughts. However, beyond conspiracy theories, the human desire to try to control the weather is not a hoax. There are already scientific studies that show that rainfall can be increased artificially through cloud seeding with silver iodide.

Why does it rain?

Can it be made to rain?

As Andrea Flossmann, co-chair of the World Meteorological Organization (WMO) group of experts in this field explains, there is currently a renewed interest in various countries in techniques capable of modifying the weather. “This is a concept that has been in the works for nearly 80 years, which first generated a lot of expectations and then collapsed completely because it could not be proven to work, but now it is making a comeback because of climate changes, as the situation becomes more desperate,” says the emeritus researcher from the University of Clermont-Ferrand (France), referring to global warming.

According to José Luis Sánchez, a professor of applied physics at the University of León, who has himself flown in planes to seed clouds, various investigations have been carried out in Spain in the past to try to artificially increase rainfall, such as the PIP project coordinated by the WMO in Valladolid between 1979 and 1981. They were not very successful: in the case of the PIP, it was not even possible to move on to the seeding phase. “Nothing has been done again, which for me is a mistake; more research needs to be done on what happens inside the clouds to understand why some precipitate and others do not,” he says. However, anti-hail nets with silver iodide burners are still used today, such as the one that has been in operation since 1976 in Madrid. In addition, there are currently farmers who buy their own anti-hail cannons with sound waves to protect their farms, although the experts consulted by this newspaper do not give much credence to the effectiveness of the latter.

As for artificial rain, water experts stress that there are simpler options for increasing the availability of water resources, such as improving efficiency or saving. Moreover, in the event of a drought, this is not a technique that can be applied everywhere, as clouds are essential. Even so, if cloud seeding with silver iodide has not become more widespread, it is because of the difficulty in proving that it really works. “The reason is the great diversity of clouds,” Flossmann explains, “we never have two identical ones, so we can seed one and not another to compare them later.”

To resolve this issue, the French meteorologist explains that there are two possible strategies. The first consists of carrying out much more massive cloud seedings hoping to find statistical differences, similar to the double-blind tests used by doctors. However, as she stresses, this has never been done because the studies are very expensive. The other strategy is being carried out and consists of focusing on clouds with less variability — orographic clouds — which are those that form in areas with relief. “It has been carried out in the Rocky Mountains, where cloud seeding has managed to increase snow, in a region where water reserves are stored for cities in summer. In this case, there is confirmation that the principle can work,” Flossmann notes.

What techniques are there for cloud seeding?

As Sánchez explains, countries such as the United States, Greece and Austria have been seeding clouds from aircraft for more than 25 years, and Canada and Bulgaria have been doing so for a little less time. Because of the use of aircraft, this is the most expensive system. The Spanish physicist jokes about the images of splendid blue skies crossed by the normal condensation trails of aircraft that are sometimes spread on social networks as if some chemical substance were being sprayed, when the real seeding necessarily takes place with clouds and sometimes in situations of great atmospheric instability.

“When you fly into a storm in an airplane, you feel like you’ve been pulled upwards, these are updrafts,” says the physicist. “In rain clouds, the updraft is tiny, at most two meters per second, but in storm clouds it can be between 10 and 30 meters per second, that’s between 35 and 100 kilometers per hour [35-62 miles per hour]. It’s very hard to get into storm clouds, but I love it,” says this expert, who shows videos of silver iodide seeding from inside airplanes in a project against hail in Mendoza (Argentina), of which he is scientific director.

In other countries, especially in Russia and China, but also in Bulgaria, Romania and Moldova, rockets launched from the ground with artillery cannons are used to spread silver iodide in the clouds. “Here the problem is that air traffic has to be stopped and that is why they are abandoning it,” says Sánchez, who adds that in Bulgaria they have asked him for advice on changing to the Spanish model.

In both France and Spain, the cloud seeding system is used to combat hail with burners installed on the ground, such as those in the regions of Madrid or Aragón. It is cheaper than airplanes and does not affect air traffic. In the case of the Madrid anti-hail network, in the 48 years it has been operating, it has always been managed by the Chamber of Agriculture and is made up of 14 automatic generators in which silver iodide is burned, located in agricultural areas in the southeast of the region. “We have a collaboration with the State Meteorological Agency (Aemet) that makes a specific prediction for this area and when there is a risk of hail greater than 50%, these are days when the generators are likely to be turned on,” explains Vicente Díez, an agricultural technical engineer from the Chamber of Agriculture in charge of the network. Despite operating since 1976, he says that they do not have data on its effectiveness. “A meteorological study is currently being carried out on the evolution of the climate in recent years in the Madrid region and neighbouring provinces,” he says.

Fight against hail

The silver iodide seeding system is the same for trying to generate artificial rain or to fight hail; the difference is in the type of clouds and their thickness. As explained by Sánchez, rain clouds usually have a vertical extension of one or two kilometers, while those that generate dangerous hail can reach more than 7.5 miles (12 kilometers) in thickness, such as the cumulonimbus clouds that usually occur in Spain in summer, when it is hotter. “At minus 12 or 15 degrees, one gram of silver iodide generates approximately one billion freezing nuclei at least, which will encourage many ice crystals inside the clouds to try to make the drops grow as they collide with each other,” explains Sánchez.

In this way, if they reach the necessary size, and depending on the temperature, they will turn into rain or snow. However, in storm clouds, which are much thicker and have a lot of water inside them, the problem is that hailstones are produced that grow too large, which can cause significant damage to agricultural fields or human settlements. Here, silver iodide tries to increase competition between ice crystals so that there is less chance of some of them becoming too big.

For Flossmann, there are several risks to be taken into account when trying to manipulate the weather. The first is the danger of spreading chemicals that have toxicity problems. According to the French meteorologist, the quantities are very small at the moment, but she believes that this should be monitored. Another sensitive issue is the lack of regulation. “At the moment, it is very different in each place and each country does what it wants,” she points out. “In France, the tests are promoted by private entities, farmers’ associations. There are countries where the meteorological services are usually in charge, while in other places like Wyoming it is scientists with water companies. And in China and Russia, it is directly the military that is in charge.”

Unlike so-called geoengineering solutions to modify climate conditions on a large scale — which are now more in the realm of theory — techniques to try to generate rain or reduce hail are much more local. However, they have another effect that is repeated all over the planet: they arouse real anger among residents.

Although hoaxes such as chemtrails sound so crazy that they seem harmless, the reality is that these types of messages related to meteorology do take hold and generate a lot of tension. In fact, there are Spanish farmers who are now convinced that the drought they are suffering is the fault of cloud seeding in Morocco, or of the private anti-hail cannons used in irrigated fields.

“When it doesn’t rain, these unfounded theories start to emerge,” says Juan Esteban Palenzuela, territorial delegate of Aemet in Murcia, who explains that the water shortage in this Spanish region, where the last hydrological year was the driest since 1961-1962, has triggered tensions between dryland farmers who accuse other irrigated farmers of causing drought with their anti-hail cannons. Supposedly, these devices reduce the size of hail using sound waves. However, according to this meteorologist, “the reality is that they have no scientific basis.” And in no case can they alter the normal rainfall pattern. In fact, as Palenzuela points out, even the sowing techniques that have proven to be more effective achieve “a little more precipitation water [...] When I say a little more, I mean that perhaps the rainfall increases by 15% or 20% at most.”

These anti-hail cannons, which are causing problems for some farmers, are sold by SPAG, based in Valencia. Alberto Gerada, director of operations for this company, does not give sales figures, but states that “we are having annual internal growth of over 100%.” Regarding the controversy caused by these devices, he acknowledges that “the social noise is enormous.” Paradoxically, he also says that “in areas of northern Europe where it rains a lot, the complaint is the opposite, because there they claim that the system increases rainfall.”

The SPAG representative claims that current devices are not like the sonic cannons of the past and guarantees that their sound waves “cause microcracks in the structure of the hail before it reaches the surface to reduce its damaging impact.” However, Sánchez also questions whether they are of any use. In Spain, the law establishes that it is the hydrographic confederations that must authorize systems that modify the atmospheric phase of the hydrological cycle in order to avoid precipitation in the form of hail.

In this regard, the Segura Hydrographic Confederation (CHS) states that “the River Basin Authority is not oblivious to the social impact that the use of these devices has caused, although it is true that it has a greater echo among certain economic sectors (mainly, the agricultural sector) and, logically, in those geographical areas where their use is more recurrent.” After analyzing what Aemet says about these cannons, the CHS concludes that “their use would have a very limited effect that could hardly be related to a decrease in rainfall in a region or a larger geographical area.”

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