Rain no longer falls from the sky by chance. Or at least, not anymore. For decades, some states have developed the ability to provoke it on demand by seeding clouds with chemical substances that force water droplets to coalesce and descend. This is no longer science fiction: it is a state policy in China, the United Arab Emirates, and in about fifty countries in total.
Key takeaways
- Thousands of rockets fire each year, releasing chemical particles into clouds to force rain
- China employs 40,000 people to manage the climate over more than half of its territory
- AI is now entering the equation, promising to make this technology more efficient and more formidable
When an airplane decides it’s going to rain
The principle is simple: you inject into a cloud particles capable of serving as a surface for water vapor. These substances introduced into the clouds act as condensation nuclei, providing a surface on which water vapor condenses or freezes, forming droplets that grow heavier and eventually fall as rain. The materials used are silver iodide, potassium iodide, or dry ice, which serve as the nuclei around which droplets form.
Concretely, in the United Arab Emirates, the process begins well before takeoff. The seeding operation is a full process that starts with data collection: radar experts, ground stations and satellites feed daily weather forecasts, before a team of meteorologists evaluates the cloud formations suitable for seeding. Once the clouds are identified, the aircraft of the National Center of Meteorology carrying salt crystals mixed with magnesium, sodium chloride and potassium chloride are sent directly into the clouds.
The country began practicing cloud seeding in the 1990s, and this technique is now used for more than 1,000 hours per year. About a thousand hours per year in one of the driest countries in the world, where the Emirates receive only about 100 mm of precipitation annually. By comparison, Paris receives six times more without any intervention.
China, or the industrialization of rain
China stands out as the main investor in the field, with all provincial governments—except Shanghai—having set up weather modification offices. Collectively, these offices employ about 40,000 people. That’s the equivalent of the entire staff of Météo-France… multiplied by ten.
China has invested massively in cloud seeding for several years. According to CNN, the country would have spent more than $1.34 billion on various climate modification programs between 2012 and 2017. In the same period, the country claimed to have increased precipitation by 316 billion tonnes. An astronomical figure, difficult to verify, but which conveys the scale of the ambitions.
The use is not limited to drought relief. The Beijing Olympics could take place without rain thanks to this technology, a demonstration before the world of China’s ability to master the elements. For the 2008 Games, China launched more than a thousand rockets to spray silver iodide into the city’s sky in an attempt to clear storm clouds. Cloud seeding in China fits into a broader state strategy to project an image of technological prowess and national mastery.
Beijing aimed to be able to make rain and fair weather over more than 5.5 million square kilometers, i.e., more than half the country, by 2025. At that time, the effort concerned only 3 million square kilometers. A constantly expanding area, and that is precisely what worries neighboring countries.
AI enters the dance
The next step is no longer in rockets or salts, but in algorithms. The latest development for triggering rain: artificial intelligence. At the International Forum on Rain Enhancement in Abu Dhabi, this technology was on everyone’s lips. A project is being implemented jointly by the United Arab Emirates National Center of Meteorology, the Mohammed bin Zayed University of Artificial Intelligence, Wuhan University and the University of California, San Diego. Its central objective: to develop a real-time, data-driven system to assess a cloud’s capacity for seeding.
The aim is to reduce failures. For the fundamental weakness of this technology remains its unpredictability. Measuring the precise impact of seeding remains one of its major challenges. We can never know exactly how much rain or snow would have fallen without intervention. Researchers’ estimates suggest seeding can amplify precipitation by about 30–35% in drier atmospheres, and by 10–15% in wetter environments. Promising on paper, but highly variable depending on local conditions.
When the clouds of one country steal rain from a neighbor
Causing rain at home sometimes means taking it away from a neighbor. Triggering rain in one zone could theoretically reduce downstream precipitation, creating disputes over water resources between territories or neighboring countries. In 2018, an Iranian general went so far as to accuse Israel of “stealing the clouds” to prevent rain from falling in Iran. An anecdote that might seem whimsical, but it reveals real geopolitical tension around water resources.
The Tibetan Plateau is the source of several major transboundary rivers, and altering the rainfall regime through cloud seeding is likely to affect the availability of water resources for downstream countries. The question is notably to what extent weather modification could bolster China’s hydraulic hegemony and generate a security dilemma with India.
An international treaty did indeed be adopted on December 10, 1976, under the United Nations, to ban the use of environmental modification techniques for military or other hostile purposes. But nothing governs large-scale civilian uses. In 2023, the European Union still did not have regulations on cloud seeding. A legal vacuum that takes on another dimension when tens of thousands of rockets are fired into the skies of a country the size of a continent each year.
The perhaps defining close note lies in the Dubai case of April 2024: 254 millimeters of rain fell in a single day, the equivalent of nearly two years’ worth of precipitation in this desert country, triggering a wave of accusations against cloud seeding. Meteorologists confirmed that these record rains were caused by a natural extratropical depression. But the reflex to blame the technology before weather science says something essential: for the first time in history, the suspicion that humans made the rain has become a credible hypothesis in the eyes of the general public.
Sources: france24.com | tameteo.com
