The global volume and distribution of modern groundwater by Tom Gleeson, Kevin M. Befus, Scott Jasechko, Elco Luijendijk & M. Bayani Cardenas, Received 18 May 2015 Accepted 14 October 2015 Published online 16 November 2015,
Nature Geoscience (2015) doi:10.1038/ngeo2590
Groundwater is important for energy and food security, human health and ecosystems. The time since groundwater was recharged—or groundwater age—can be important for diverse geologic processes, such as chemical weathering, ocean eutrophication and climate change. However, measured groundwater ages range from months to millions of years. The global volume and distribution of groundwater less than 50 years old—modern groundwater that is the most recently recharged and also the most vulnerable to global change—are unknown. Here we combine geochemical, geologic, hydrologic and geospatial data sets with numerical simulations of groundwater and analyse tritium ages to show that less than 6% of the groundwater in the uppermost portion of Earth’s landmass is modern. We find that the total groundwater volume in the upper 2 km of continental crust is approximately 22.6 million km3, of which 0.1–5.0 million km3 is less than 50 years old. Although modern groundwater represents a small percentage of the total groundwater on Earth, the volume of modern groundwater is equivalent to a body of water with a depth of about 3 m spread over the continents. This water resource dwarfs all other components of the active hydrologic cycle.
Groundwater is mostly non-renewable, study finds, Less than 6% of groundwater is replenished within 50 years by Emily Chung, November 16, 2015, CBC News
Billions of people around the world rely on groundwater for drinking, washing and farming.
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While many people may think groundwater is replenished by rain and melting snow the way lakes and rivers are, underground water is actually renewed much more slowly.
In fact, just six per cent of the groundwater around the world is replenished within a “human lifetime” of 50 years, reports University of Victoria hydrogeologist Tom Gleeson and his collaborators in a new study published in the journal Nature Geoscience today.
That water tends to be mainly found within a few hundred metres of the surface, where it is most vulnerable to being contaminated by pollution or depleted by higher temperatures and reduced rainfall as a result of climate change, the researchers found.
“Groundwater is a super-important resource,” Gleeson said in an interview with CBC News. “It’s used by more than a third of the world’s population every day for their drinking water and it’s used by agriculture and industry.”
More than a third of the Canadian population relies on groundwater, including the entire population of P.E.I. and some fairly large urban centres such as Kitchener-Waterloo, Cambridge and Guelph in Ontario, Gleeson added.
Because groundwater is so important to billions of people around the world, Gleeson and colleagues at the University of Texas at Austin, the University of Calgary, and the University Gottingen were interested in finding out how much groundwater there is in the world and to get an idea of when it will run out.
Scientists had previously made a rough estimate of the amount of groundwater in the world, but no one knew how much is renewable and how quickly it’s replenished.
Gleeson and his colleagues came up with a way to figure out what groundwater was less than 50 years old. In the 1960s, during the Cold War, a number of countries were doing above-ground nuclear testing. This introduced a radioactive form of hydrogen, called tritium, into the world’s water supply.
The researchers figured that groundwater with high levels of tritium was renewed since the 1960s. Groundwater with negligible levels was older.
By looking at 3,500 measurements of tritium in groundwater from 55 countries and using computer models to trace the flow of groundwater around the world, they were able to estimate how much groundwater was young and renewable and how much was older.
They also confirmed the total quantity of groundwater around the world using a variety of data like the permeability of rock to the flow of water and how much water could be stored in different places, based on how porous the rock there was.
A look at previous estimates of total groundwater showed the crude calculations were not far off.
“When we actually went back and traced what the actual calculation, it was literally two lines of text that someone could do at a bar,” Gleeson said. “But the amazing thing was that they were right.”
His team came up with almost exactly the same number.
Plentiful but finite
They estimated that the total amount of groundwater in the world was 22.6 million cubic kilometres — enough to cover all the land on Earth to a depth of 180 metres. The amount that was renewable was no more than 1.3 million cubic kilometres or less than six per cent. But the researchers said that was likely an overestimate due to the types of rock in the areas where most of the measurements were taken. Correcting for that suggested that the actual amount of groundwater renewable within 50 years was likely only 0.35 million cubic kilometres, or enough to cover all the land on Earth to a depth of just three metres.
The good news is that the amount of renewable groundwater on Earth is quite large —- three times larger than all other fresh water contained in lakes and rivers on Earth, the researchers reported.
But it isn’t evenly distributed. There was less groundwater, especially younger groundwater, in more arid regions.
Gleeson said in places like California and the U.S. Midwest, people are already using “non-renewable” water that is thousands of years old and in places such as Egypt, they’re tapping into water that may have last been renewed a million years ago. Such old water isn’t just non-renewable — it tends to be saltier and more contaminated than younger groundwater.
In addition, overusing groundwater, either old or young, can lower subsurface water levels and dry up streams, which could have a huge effect on ecosystems on the surface, Gleeson added.
He hopes the study will help remind and motivate people to manage their groundwater resources better. “And realize that it’s finite and a limited resource that we need to respect and manage properly.”
Study shows Earth’s groundwater mostly unrenewable by Colette Derworiz, November 16, 2015, Calgary Herald
An international team of hydrologists has found that much of the Earth’s groundwater isn’t renewable within a human lifetime after mapping out the important resource.
The study, published Monday in the journal Nature Geoscience, was led by Tom Gleeson at the University of Victoria with co-authors from the University of Texas, University of Calgary and University of Göttingen in Germany.
“The goal of this study was to calculate, for one of the first times, how much groundwater we have on this planet,” said Scott Jasechko, an assistant professor in the U of C’s department of geography who co-authored the study. “This is water that is held within pore spaces in rock and soils underneath our feet.
“Of all of the fresh and unfrozen water on this planet, about 99 per cent is groundwater.”
The research estimates a total volume of nearly 23 million cubic kilometres of total groundwater. To put that into perspective, if you pooled all of the groundwater in the world on top of the land, it would be 180 metres deep — almost as tall as the Calgary Tower.
Although the volume is immense, Jasechko said only a small, finite fraction of the resource is being replenished.
The study showed that six per cent of water in the uppermost portion of the Earth’s landmass is renewable within a human lifetime or 50 years.
The research comes as the global demand for water grows, particularly with climate change.
Jasechko said it provides important information for water managers and policy developers, as well as scientists, to manage groundwater resources in a more sustainable way.
“This groundwater resource is finite,” he said. “There’s only so much and developing management time horizons on decade-old timeframes is important, but we need to make sure we have a strong understanding of just how much groundwater is available.”
Groundwater is an important resource, with about two billion people worldwide relying on it for drinking water. About 40 per cent of irrigation used for food production uses groundwater, said Jasechko.
It’s also supplies water and nutrients sustaining aquatic ecosystems in lakes and rivers.
“We should use a longer time horizon when making decisions because the amount of modern groundwater is finite, vulnerable to climate change, susceptible to pollution, and needed by natural ecosystems,” he said.
The study was funded by the Natural Sciences and Research Council, Canadian Institute for Advanced Research, US National Science Foundation and the American Geophysical Union.
[Refer also to:
AEA: Support to the identification of potential risks for the environment and human health arising from hydrocarbons operations involving hydraulic fracturing in Europe by the European Commission DG Environment, prepared by AEA Technology plc under contract to the European Commission DG Environment ref 07.0307/ENV.C.1/2011/604781/ENV.F1., August 10, 2012, Ref: AEA/ED57281/Issue Number 17
For individual sites with less than 600 m separation between the fracturing zone and groundwater, the risk was judged “high”.
A proportion (25% to 100%) of the water used in hydraulic fracturing is not recovered, and consequently this water is lost permanently to re-use, which differs from some other water uses in which water can be recovered and processed for re-use.
Drilling and hydraulically fracturing wells can be water-intensive procedures; however, there is very limited Canadian experience from which to estimate potential environmental impacts.
Flow-back water is infrequently reused in other fracs because of the potential for corrosion or scaling, where the dissolved salts may precipitate out of the water and clog parts of the well or the formation.
Little is known about what the ultimate impact on freshwater resources will be.