Study is first to map Earth’s hidden groundwater

If all the Earth’s modern groundwater was pooled above ground, how deep would it be? Credit: Karyn Ho

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.


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.



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 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.

Tom Gleeson, Kevin M. Befus, Scott Jasechko, Elco Luijendijk, M. Bayani Cardenas. The global volume and distribution of modern groundwater. Nature Geoscience, 2015; DOI: 10.1038/ngeo2590
