海角大神

Fresh water on Earth is scarce and getting scarcer 鈥� we know that. In 2015 the World Economic Forum ranked "water crises" as facing the planet.聽

But authors of a recent report published Friday in the journal Science Advances say previous studies have underestimated the severity of water scarcity around the world. Instead of impacting around two billion people as researchers previously suggested, it鈥檚 more along the lines of four billion, say Dr. Mesfin Mekonnen and Dr. Arjen Hoekstra at the University of Twente in Enschede, Netherlands.

So how has previous research been so off? It relied on annual averages, say the authors.聽

鈥淢ost of the previous water scarcity studies are done on an annual basis, which hides the actual variability within a year,鈥� co-author Dr. Mekonnen, a postdoctoral researcher at the University of Twente, tells 海角大神 in an email Thursday. To understand water scarcity on the global level, Mekonnen and Hoekstra assessed local "blue water scarcity," or the amount of freshwater that is withdrawn and not returned, on a monthly level.聽

But these four billion people are not facing water scarcity all year round, notes Mekonnen, instead it鈥檚 more along the lines of one month a year.聽

鈥淲hen you average over the whole year, you miss that one month where [a] large number of people face water scarcity,鈥� says Mekonnen. 鈥淏efore we thought only [a] small number of people face severe water scarcity,鈥� but a larger population鈥檚 few, difficult months were skewing the annual average.

鈥淲ater scarcity generally occurs only during part of the year, when there is a mismatch between water availability and demand,鈥� explains Mekonnen. Only half a billion people actually experience water scarcity for the entire year.聽

The truth about water scarcity鈥檚 impact is important, say the authors, because informed consumers are more likely to 鈥� and pollution underlying consumer products from business and governments,鈥� Dr. Hoekstra explains in a paper published last year.聽And the most water-demanding products are not always the most obvious.

鈥淟ittle interest in water has been shown in the meat and dairy sectors, which is surprising given the fact that the meat and dairy sectors to the global water footprint of humanity,鈥� says Hoekstra. 聽聽

Their study also breaks down a presumed barrier between developed and underdeveloped countries, instead suggesting water scarcity may be more correlated to population levels.聽

In their study, Mekonnen and Hoekstra suggest India and China, the two most populated countries, are home to up to half of the total four-billon people experiencing water scarcity. Other significant populations facing severe water scarcity live in Bangladesh, the United States, Pakistan, Nigeria, and Mexico 鈥� five of the 10 most populated in the world.

And a detailed breakdown of water-stressed months makes mitigation efforts more realistic, say Mekonnen and Hoekstra.聽

鈥淕overnments should put a cap on water footprints, per river basin and per month, to ensure that water consumption doesn鈥檛 exceed maximum sustainable levels,鈥� Mekonnen tells The Monitor. 鈥淲ithout proper measurement of the extent of the water scarcity, it will be difficult to design proper response strategies to address the problem. By measuring the water scarcity level properly, we are able to assess the human, economic, social, and environmental costs.鈥�