Many parts of the world are predicted to endure "day-zero droughts," periods of extreme and unprecedented water scarcity, which could happen as soon as this decade in certain hotspots including parts of North America, the Mediterranean and southern Africa, according to a new study. It's well known that climate change, driven by burning fossil fuels, is throwing the global water cycle off balance and causing scarcity. What's much less clear is when and where extreme water shortages will hit. The new research helps provide answers and some of them are surprising, said Christian Franzke, a climate scientist at Pusan National University in South Korea and an author of the study published in Nature Communications. The scientists used a large number of climate models to assess the timing and likelihood of day-zero droughts. These are "unprecedented water scarcity events, events which haven't occurred so far," Franzke said. It's when "you turn on your water tap and no water comes out," he told CNN. Nearly three-quarters of drought-prone regions, including those with major reservoirs, face a high risk of severe and persistent droughts by the end of the century if humans keep burning planet-heating fossil fuels, the study found. More than a third of these regions, including the western United States, could face this situation as early as the 2020s or 2030s. The finding that day-zero droughts could happen so soon, at current levels of global warming, was "something that surprised us," Franzke said, even though a few cities have already come perilously close. Read more at the link in our bio. 📷: Rodger Bosch/AFP/Getty Images