LONDON, Nov 16 (Thomson Reuters Foundation) - The first map showing the world's hidden groundwater was published on Monday, bringing us closer to estimating how much there is, and when it will run out if we over-use the resource. 
 
 Using data and computer models, an international team of researchers estimated that less than six percent and perhaps as little as one percent of water found close to the Earth's surface is renewable in a human lifetime. 
 
 "This has never been known before," Tom Gleeson of Canada's University of Victoria and the lead author of the study, said in a statement. 
 
 "We already know that water levels in lots of aquifers are dropping. We're using our groundwater resources too fast - faster than they're being renewed." 
 
 The study, published in the journal Nature Geoscience, estimated a total volume of underground water to be almost 23 million cubic kilometres, of which 0.35 million cubic kilometres is younger than 50 years old. 
 
 Underground water is found beneath the Earth's surface and is recharged by rain, snow or water that leaks from the bottom of lakes and rivers. 
 
 Its age can be a few months to millions of years. It can be found as deep as 30,000 feet (around 9 km), according to the United States Geological Survey (USGS). 
 
 "Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out," Gleeson said. 
 
 Although water found closer to the surface is being renewed quicker than the water found deeper in the Earth, it is more sensitive to contamination and climate change, but it can also serve to temper climate extremes, Gleeson said. 
 
 Water found deeper in the Earth is often used for agriculture and industry. It can contain arsenic or uranium and is often more salty than seawater, he added. 
 
 "Groundwater can and should be thought of as a very useful buffer to climate extremes," Gleeson told the Thomson Reuters Foundation in a phone interview from Canada. 
 
 "If properly managed it flows to rivers during times of drought so it's a valuable and strategic resource for mitigating the extreme impacts of climate on water availability." 
 
 According to the study, most groundwater is found in tropical and mountainous regions, with some of the largest deposits in the Amazon Basin, the Congo, Indonesia and along the western borders of North and South America. 
 
 Not surprisingly, the least amount is in arid regions such as the Sahara. (Reporting by Magdalena Mis; Editing by Ros Russell; Please credit Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, corruption and climate change. Visit www.trust.org) ||||| Groundwater: it's one of the planet's most exploited, most precious natural resources. It ranges in age from months to millions of years old. Around the world, there's increasing demand to know how much we have and how long before it's tapped out. 
 
 For the first time since a back-of-the-envelope calculation of the global volume of groundwater was attempted in the 1970s, an international group of hydrologists has produced the first data-driven estimate of the Earth's total supply of groundwater. The study, led by Dr. Tom Gleeson of the University of Victoria with co-authors at the University of Texas at Austin, the University of Calgary and the University of Göttingen, was published today in Nature Geoscience. 
 
 The bigger part of the study is the "modern" groundwater story. The report shows that less than six per cent of groundwater in the upper two kilometres of the Earth's landmass is renewable within a human lifetime. 
 
 "This has never been known before," says Gleeson. "We already know that water levels in lots of aquifers are dropping. We're using our groundwater resources too fast--faster than they're being renewed." 
 
 With the growing global demand for water--especially in light of climate change--this study provides important information to water managers and policy developers as well as scientists from fields such as hydrology, atmospheric science, geochemistry and oceanography to better manage groundwater resources in a sustainable way, he says. 
 
 Using multiple datasets (including data from close to a million watersheds), and more than 40,000 groundwater models, the study estimates a total volume of nearly 23 million cubic kilometres of total groundwater of which 0.35 million cubic kilometres is younger than 50 years old. 
 
 Why is it important to differentiate old from modern groundwater? Young and old groundwater are fundamentally different in how they interact with the rest of the water and climate cycles. Old groundwater is found deeper and is often used as a water resource for agriculture and industry. Sometimes it contains arsenic or uranium and is often more salty than ocean water. In some areas, the briny water is so old, isolated and stagnant it should be thought of as non-renewable, says Gleeson. 
 
 The volume of modern groundwater dwarfs all other components of the active water cycle and is a more renewable resource but, because it's closer to surface water and is faster-moving than old groundwater, it's also more vulnerable to climate change and contamination by human activities. 
 
 The study's maps show most modern groundwater in tropical and mountain regions. Some of the largest deposits are in the Amazon Basin, the Congo, Indonesia, and in North and Central America running along the Rockies and the western cordillera to the tip of South America. High northern latitudes are excluded from the data because satellite data doesn't accurately cover these latitudes. Regardless, this area is largely under permafrost with little groundwater. The least amount of modern groundwater is not surprisingly in more arid regions such as the Sahara. 
 
 "Intuitively, we expect drier areas to have less young groundwater and more humid areas to have more, but before this study, all we had was intuition. Now, we have a quantitative estimate that we compared to geochemical observations." says Dr. Kevin Befus, who conducted the groundwater simulations as part of his doctoral research at the University of Texas and is now a post-doctoral fellow at the United States Geological Survey. 
 
 The next step in painting a full picture of how quickly we're depleting both old and modern groundwater is to analyze volumes of groundwater in relation to how much is being used and depleted. 
 
 In a previous study that ultimately led to the investigation of modern groundwater, Gleeson's 2012 groundwater footprint report in Nature mapped global hot spots of groundwater stress, charting rates of precipitation compared to the rates of use through pumping, mostly for agriculture. Some of these hot spots are northern India and Pakistan, northern China, Iran, Saudi Arabia, and parts of the US and Mexico. 
 
 "Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out," says Gleeson. To do this, he will be leading a further study using a global scale model. 
 
 ### 
 
 Funding for this study came from Natural Sciences and Research Council, Canadian Institute for Advanced Research, US National Science Foundation and the American Geophysical Union. 
 
 The global volume and distribution of modern groundwater: http://nature. com/ articles/ doi:10. 1038/ ngeo2590 
 
 Note: This url will automatically redirect to the paper once it's published online (Nov. 16, 8 a.m. PST). 
 
 Modern groundwater map and photo of Dr. Tom Gleeson available for download at this DropBox link: http://ow. ly/ UuLdh 
 
 Media contacts: Tom Gleeson (Engineering) at 250-853-3934 or tgleeson@uvic.ca 
 
 Suzanne Ahearne (University Communications + Marketing) at 250-721-6139 or sahearne@uvic.ca 
 
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 This story was originally published by Reveal from the Center for Investigative Reporting and is republished here as part of the Climate Desk collaboration. 
 
 By now, the impacts of California’s unchecked groundwater pumping are well-known: the dropping water levels, dried-up wells and slowly sinking farmland in parts of the Central Valley. 
 
 But another consequence gets less attention, one measured not by acre-feet or gallons-per-minute but the long march of time. 
 
 As California farms and cities drill deeper for groundwater in an era of drought and climate change, they no longer are tapping reserves that percolated into the soil over recent centuries. They are pumping water that fell to Earth during a much wetter climatic regime—the ice age. 
 
 Such water is not just old. It’s prehistoric. It is older than the earliest pyramids on the Nile, older than the world’s oldest tree, the bristlecone pine. It was swirling down rivers and streams 15,000 to 20,000 years ago when humans were crossing the Bering Strait from Asia. 
 
 “What I see going on is a future disaster,” says Vance Kennedy, a retired research hydrologist. “We are mining water that cannot be readily replaced.” 
 
 Tapping such water is more than a scientific curiosity. It is one more sign that some parts of California are living beyond nature’s means, with implications that could ripple into the next century and beyond as climate change turns the region warmer and robs moisture from the sky. 
 
 “What I see going on is a future disaster. You are removing water that’s been there a long, long time. And it will probably take a long time to replace it. We are mining water that cannot be readily replaced,” said Vance Kennedy, a 91-year-old retired research hydrologist in the Central Valley. 
 
 Despite such concern, the antiquity of the state’s groundwater isn’t a well-known phenomenon. It has been discovered in recent years by scientists working on water quality studies and revealed quietly in technical reports. 
 
 Groundwater is crucial to California. In an average year, nearly 40 percent of the state’s water comes from underground sources. In the current extended drought, it’s more than half. Eighty percent of California residents rely to some degree on groundwater. Some towns, cities and farming operations depend entirely on it. 
 
 Groundwater is like a bank account. You want to balance the debits and credits, not draw down the principal. But California has been depleting its groundwater principal for generations, pumping more than nature can replenish. So, too, has the United States as a whole. The biggest overall user is agriculture. 
 
 “If we continue irrigating at the increasing rates that we are in the US, the bottom line is that can’t be sustained,” said Leonard Konikow, a retired US Geological Survey hydrogeologist in Virginia. “That can’t go on forever.” 
 
 Over the past century, US groundwater has been depleted by nearly 1,000 cubic kilometers—about twice the volume of Lake Erie. 
 
 A new article by Konikow in the journal Groundwater estimates that nearly 1,000 cubic kilometers—about twice the volume of Lake Erie—was depleted across the United States from 1900 to 2008. That’s enough to contribute to rising sea levels, along with melting glaciers and polar ice. 
 
 “That really surprised a lot of people,” Konikow said. 
 
 The pace of depletion has jumped dramatically since 2000. And Konikow identified one area that appears to have the most serious depletion problem in the nation—California’s agricultural powerhouse, the Central Valley, especially its more arid southern portion. 
 
 How long the bounty can last is anyone’s guess. As wells are drilled deeper, pumping costs soar. Water quality can suffer. In some areas, the earth itself is starting to sink as deep aquifers are pumped to historic low levels. 
 
 That problem is known as subsidence, and it’s a big deal. As the land sags, it is harming water delivery canals, damaging wells and buckling pavement. 
 
 “The rates of subsidence we are seeing are about a foot per year in some areas. They are just phenomenal,” said John Izbicki, a research hydrologist with the US Geological Survey. 
 
 The last time this happened, during a binge of overpumping in the 20th century, one part of the valley sank 28 feet and damages topped $1.3 billion (in 2013 dollars), according to the California Water Foundation. 
 
 But that’s not all: As those deep aquifers are pumped, they suffer structural damage and no longer hold as much water as before. To visualize what happens, imagine a kitchen sponge. 
 
 “You take it out of the package and it’s all nice and fluffy,” said Bryant Jurgens, a research hydrologist with the US Geological Survey. “After a month of use, it starts to shrink. When you wet it again, it doesn’t ever quite get as big as it originally was. That’s exactly what happens to the aquifer.” 
 
 And some of that water, as it turns out, is quite ancient. If you bottled it, you could label it the provenance of the Pleistocene—a geological epoch that lasted from about 2.5 million to 12,000 years ago. 
 
 The landscape was much different back then. Yosemite Valley was a river of ice. Mastodons and other now-extinct creatures roamed the West Coast. To the east and south, lakes stretched for miles across terrain we now call desert. 
 
 All water, in a sense, is ancient. It’s been cycling through clouds, rivers, forests and oceans for millions of years. But in recent decades, scientists have found ways to determine roughly when precipitation fell to earth and percolated into the surface, becoming groundwater. 
 
 Water pumped from some wells in the Central Valley is 10,000 to more than 30,000 years old. 
 
 They do it by testing water for the presence of certain compounds that decay slowly over time, such as carbon-14, a radioactive isotope that also is used to estimate the age of ancient civilizations and human ancestors. 
 
 There is no point-and-click website that reveals the age of groundwater in the state. To access the information, you must wade through a tangle of studies compiled by the US Geological Survey as part of a state-funded public drinking water-quality monitoring program. 
 
 The jargon in those studies is so thick it is nearly incomprehensible. But deep in the scientific sediment are nuggets worth sharing with friends—a sentence here, a table there. They show water pumped from some deep public supply wells in the valley is 10,000 to more than 30,000 years old. Similar ages also have been reported in many desert basins, including Coachella Valley and Owens Valley, a major source of drinking water for Los Angeles. 
 
 What that means for the future is uncertain. Even though many areas pump more water than is recharged naturally, there is still more groundwater to be pumped. 
 
 “We are withdrawing from a fairly large bank account,” said Tom Myers, a hydrogeologic consultant in Reno, Nevada, who has worked in Southern California. “But we are withdrawing from it a lot faster than we are putting back in. The problem is we don’t know how close it is to empty.” 
 
 And many areas also recharge aquifers with surface water imported from elsewhere. 
 
 “There are places where you could be pumping very old groundwater and there is sufficient recharge to the system—so it’s not necessarily a problem,” said Miranda Fram, a research chemist with the US Geological Survey. “But in many cases, it is. It’s mining old groundwater that’s not being replenished.”
– "We're using our groundwater resources too fast—faster than they're being renewed," Dr. Tom Gleeson says in a University of Victoria press release. Gleeson, along with fellow researchers, published the most accurate map of Earth's groundwater supply to date on Monday in Nature Geoscience. The study found there is about 14.3 million cubic miles of groundwater left on Earth. But that's not as encouraging as it sounds, according to Reuters, because no more than 6% of it is renewable within a human lifetime. "That's never been known before," says Gleeson, who adds that people are going to need to manage that resource better as water demands grow amid ongoing drought. "Groundwater can and should be thought of as a very useful buffer to climate extremes," he says. "It's a valuable and strategic resource for mitigating the extreme impacts of climate." The amount of groundwater less than 50 years old is enough to cover every continent with approximately 10 feet of water, according to the study. But while that young groundwater is more quickly replenished, it's also more easily polluted by people and impacted by climate change, Reuters reports. The rest of Earth's groundwater—which can be millions of years old—is much deeper underground and can be extremely salty and contain harmful elements, according to the press release. The next step is to figure out how dire the situation is. "Since we now know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out," Gleeson says. (But at least we might have more helium left that we thought.)