Canons blazed and aircraft deployed their payloads, but not a drop of blood was shed in the battle between the cities of Pingdingshan and Zhoukou in Henan province, China, on 10 July last year. That's because their targets weren't people, but clouds. The blistering dry spell that struck the province threatened to cause water shortages and ruin crops. The problem was frustratingly clear: though clouds drifted across the skies, too few would give up their water as rain. To coax the water out, Pingdingshan meteorologists decided to resort to a controversial practice they believed would help the heavens break, called cloud seeding. Anti-aircraft guns and rockets were used to bombard pregnant clouds with a fine spray of silver iodide crystals in the hope they would prompt large droplets to form in the cloud, and thus produce more rain. A few hours later it looked like their gambit had paid off. Westerly winds blew the clouds over Pingdingshan, where they dropped 10 centimetres of rain. But later that day only 2.5 centimetres of rain fell over Zhoukou, further east.
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