Artificial clouds to fight drought. And the cloud seeding, literally “cloud seeding”, a technique that artificially stimulates rainfall by seeding it with particular salts, such as silver iodide. Born after the Second World War, today it is used in the western United States, Mexico, Cuba, Israel and, increasingly, in the United Arab Emirates. A possible cause of the record rain that fell on Dubai on April 16th and part of the Arabian peninsula (over 140 millimeters of rain in 24 hours in an area that on average receives 95 in a year), leaving meteorologists astonished?
«A rumor which has spread online because the United Arab Emirates, a country with very little rain, is investing heavily in cloud seeding, as well as China – Vincenzo Levizzani, research director of the Institute of Atmospheric and Climate Sciences of the Cnr immediately clarifies -. The violent storm that hit Dubai rather, it is an extreme event linked to climate change». Levizzani, 67 years old, professor of Cloud Physics at the University of Bologna close to retirement, has dedicated his life to the study of clouds. I belong to him When it rains outside. History and future of rain, The Book of Clouds And Small manual for cloud seekersall for the Assayer.
Professor, what happened in Dubai then?
«Global warming is responsible for the change in the way air masses move in the atmosphere and consequently also for the formation of precipitating systems, such as thunderstorms. What is happening is that the same amount of water is raining globally across the entire Earth as it once did (2.1 millimeters per year across the entire surface, ed) but the general circulation of the atmosphere has changed so if it used to rain in the right seasons this no longer happens. Not only that: climate models tell us that it will rain much more where it used to rain a lot, while it will rain less and less where it rains little. The monsoon areas will therefore be affected by even more violent rains while the Horn of Africa, where rainfall is rare, will see less and less rain. Even in the United Arab Emirates we are starting to see extreme phenomena, both in terms of very heavy, intense and localized rainfall, and prolonged droughts.”
What is “cloud seeding”?
«To understand this technique we need to make a reference to cloud physics. In clouds, droplets and crystals form from the condensation of water vapor when it reaches above 100% saturation but, and this is the point, not only for this reason. If we only had water vapor in the atmosphere we would have saturations of 300, 400% while we have maximum saturations of 1 or 2% above 100%. In simple words we have no possibility of forming clouds with water vapor alone. It can be done in the laboratory and not in the atmosphere. Nature puts aerosol particles into circulation in the atmosphere, i.e. particles of sodium chloride (salt) that come from the surface of the sea, or of clay and kaolinite that come from the degradation of soils, such as deserts. Or that come from human production, vehicular traffic, heating and industries. These particles are called “condensation nuclei” or “ice nuclei” depending on whether they nuclei droplets or crystals, and they cause the aerosol droplets to attract water molecules and form the droplets or crystals. That is, they ensure that clouds can form when there is water vapor at a saturation of 101, 102%. Without these particles clouds do not form. Man thought of building particles in the laboratory similar to those produced in nature and placing them in the clouds to increase the precipitating power of the cloud.”
Why don’t you think Dubai’s heavy rain was caused by cloud seeding?
«Because the effectiveness of this technique is far from proven, so much so that the experiments of cloud seeding they have been abandoned almost everywhere in the world, even by those who practiced them the most. Basically, in one cloud I can get a good result, in the one next to it I can’t because all the clouds are different from each other. The United Arab Emirates are a very rich country, which has decided to invest in the scientific research of this technique but only the scientific publications that can verify their effectiveness can say whether these experiments have results. After all, this is physics… Italy? I don’t know that he uses it.”
What are the limits of this technique?
“Why the cloud seeding temperature, circulation of air masses and humidity are important functions. It is not possible to seed an atmosphere completely free of clouds. To cause rain, I must already have clouds that must be somewhat prone to producing precipitation, a condition that can only be understood from weather forecast models, that is, whether clouds capable of producing rain will form on a given day. In essence, I can seed clouds that already exist and which will perhaps produce little rain.”
Other limits?
“It is very expensive. The “bombing” of the clouds occurs through airplane flights and several thousand euros are spent on each trip. The plane flies over the cloud, when it is above it it releases particles of silver iodide, the salt most used to seed it. They are artificially produced bars which, when burned, produce particles while in the past rockets were used which were exploded inside the cloud but, I repeat, we must have the possibility of verifying that this technique actually produces results”.
April 18, 2024
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