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Science & Technology

Artificial rain: miracle cure or sorcerer’s trick?

Translated Sunday 6 September 2015, by Adrian Jordan

Currently, we reopen the debate on cloud seeding to induce rain, a return to a practice of questionable efficacy and with consequences unknown to a divided scientific community.

In the United Arab Emirates, among the world’s most arid countries, any method is a good method for making it rain. On average 78mm of rain falls each year... compared to 1220mm in Great Britain, according to World Bank data. Surely more effective than a rain-dance – although the question is debatable – for a short while the country has been experimenting with a new method: dispersing salt (sodium chloride) crystals in the clouds, with the aim of augmenting condensation and inducing liquefaction. In fact the objective is to find an alternative to the very expensive sea water desalination plants. The Emirates produces14 percent of the world’s desalinated water, making the country the second largest producer of fresh water after its neighbour Saudi Arabia. “Four days of heavy rain in Abu Dhabi produced the equivalent of nine years’ production of a desalination plant”, enthused Omar Al Yazeedi, head of research at the United Arab Emirates National Centre of Meteorology and Seismology. According to the institute, production of 100 million cubic metres of fresh water through cloud seeding costs 7 million euros per year, as against 53 million through a desalination plant. Cheaper, more efficient: the information should always be carefully examined, this type of study often being commissioned by governments which are both referee and player.

A method always used by many countries…

It is not the United Arab Emirates’ first attempt. During the summer of 2010, a government project caused 50 rainfalls around Abu Dhabi. The technology used at the time was very different: it constituted metal umbrellas 10m in diameter, designed to electrically charge the atmosphere. The negative ions produced discharged into the air, aggregating dust, which provides an ideal base for the naturally occurring water vapour to condense upon. This mechanism was deployed 74 times over 112 days, when humidity was over 30 percent. Other procedures exist. Amongst them, evidently, the famous cloud seeding, whether this be with silver iodide or sodium chloride. Used for the first time in the United States in 1946, in an effort to fight the drought which struck the New York area, this method has always been used by many countries... among them France. The latter is actually subject to this kind of experiment, lead by certain farming communities and sometimes chaperoned by local authorities on a different scale. The procedure not only has the aim of combating drought, but equally, in a storm, reduces the risk of hail, sometimes devastating for crops.

However, the efficacy of artificial rain is not unequivocal. According to François Bouttier, researcher at Météo France, data gathered and published by public bodies are too few to judge the efficiency of these methods. “For the moment, the scientific community lacks perspective.” So, the Abu Dhabi project, started in 2010, has been a big secret. It must be said that these technologies, which echo those of geoengineering which seeks to manipulate the climate, are the subject of many controversies.

Silver chloride, oddly, is known to be insoluble in water and to dangerous. Several medical articles have shown that humans absorb it through respiration and the skin, causing irritation, renal and pulmonary scarring, in severe cases leading to haemorrhaging, gastro-enteritis and increased heart-rate. However, François Bouttier says “For silver chloride to have an impact on humans, its concentration must be very much greater than that utilised in cloud seeding. Studies show that the product significantly dilutes in the atmosphere”, he insisted, while noting: “Silver ions have more serious effects on aquatic plants and animals, for which they remain very toxic.”

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