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In the United Arab Emirates (UAE), water is more valuable than oil. To support its citizens, the nation relies on expensive campaigns of cloud seeding from aircraft, which spray particles(喷洒微粒) into passing clouds to make rainfall.

But according to Oliver Branch, a climate scientist, there may be another method to stir up a rainmaker: with city-size solar farms that create their own weather. The heat from dark solar panels can cause updrafts that sometimes lead to rainstorms, providing water for local people. "Maybe it's not science fiction that we can produce this effect," says Branch, who led the work.

Few studies have examined how renewable energy might shift weather patterns. In 2020, Branch found that incredibly large solar farms, taking up more than 1 million square kilometers in the Sahara desert, could boost local rainfall. But the reward would come with a cost, the researchers found: By altering wind patterns, the solar farms would push tropical rain bands north. That's not good news for the Amazon areas.

To find more, researchers turned to a weather model that can account for land surface changes. They modeled the solar farms as nearly black fields that absorbed 95%of the sunlight, surrounded by relatively reflective sand. When the solar farms reached 15 square kilometers, they found, the increased heat they absorbed appreciably increased the updrafts, or convection, that drive cloud formation.

Hacking convection wasn't enough, however: damp air was also needed. When conditions were ripe, the model also found, a 20-square-kilometer solar field would increase a storm's total rainfall by nearly 600,000 cubic meters. If such rainstorms occurred 10 times in one summer, they would provide enough water to support more than 30,000 people for a year.

Solar farms in China and elsewhere are nearly big enough, Branch says. If they were built in the right spots, it wouldn't take much to darken the panels and to plant dark crops between panel rows. Still they're trying to improve the realism of their solar panel simulations by cross-checking them with field measurements at existing solar farms.

The UAE "is committed to studying the potentially dynamic strategies, such as optimizing convection," says Alya Al, director of the UAE's Research Program. For now, she adds, the UAE is deeply committed to its cloud seeding program, carrying out some 300 missions each year.