Our directory of things of interest

University Directory

Earth’s hidden groundwater

Earth’s hidden groundwater Somsak Nitimongkolchai
18 Nov
2015
For the first time, scientists have been able to calculate the quantity of groundwater up to two kilometres beneath Earth’s crust. They found that less than six per cent of it is renewable within a human lifetime

There are two main types of groundwater: old ‘fossil’ water, sometimes in excess of one million years old, and young ‘modern’ water that renews within months to decades. While old water is often deeper and more stagnant, modern groundwater is more important to humanity – it replenishes itself quicker and interacts with the hydrological cycle. A new study by an international team of hydrologists, calculates and maps the amount of usable, modern water beneath our feet.

‘We found an approximate total of  22.6 million cubic kilometres of groundwater within 2km of the Earth’s crust,’ says Dr Elco Luijendijk, co-author of the study and hydrologist at the University of Göttingen. ‘Of this total, less than six per cent is modern groundwater – reserves that have recharged within the last 50 years or roughly a human lifetime.’

Although modern groundwater represents such a small fraction of the total, it is enough to cover the land surface of the continents in a flood three metres deep. ‘While we were surprised at how small the percentage is, modern groundwater is by far the largest component in the active hydrological cycle,’ says Luijendijk. Nonetheless, modern groundwater is more vulnerable to contamination and over-exploitation and is being used far quicker than it is replenished, the authors say.

water3Locations of the Earth’s young, ‘modern’ groundwater, the kind that is most useful to humans (Image: Karyn Ho)

‘Groundwater is an immense resource, however the amount of time that matters for it is much longer than we usually consider,’ says Dr Kevin Befus, hydrologist at the University of Texas and co-author of the study. Luijendijk says ‘because policy makers can’t see it, protecting water sources tends to focus on smaller aspects of the hydrological cycle, for example rivers, rainwater and lakes.’

Geographically, modern groundwater tends to be found in humid and mountainous areas. The map shows bigger stores beneath the Amazon, the Congo, Indonesia and the mountains of North America along the Rockies and the western cordillera to the tip of South America. The map largely excludes high latitude, northern regions of Asia and North America as this is where permafrost – which blocks groundwater recharge – exists.

‘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,’ says Befus. ‘Now we have a quantitative estimate.’

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in PLACES...

Water

A new device, developed at ETH Zurich, could help communities…

Forests

A new initiative to save mangrove forests in the Dominican…

Deserts

The semi-autonomous Russian republic of Kalmykia sits at the forefront…

Cities

In Mogadishu, the troubled capital of Somalia, tentative moves towards…

Mountains

Researchers have predicted the birth of a new mountain range,…

Forests

Archaeological work around Lake Malawi suggests that humans manipulated the…

Water

Maida Bilal risked all to prevent contractors building a dam…

Places

Writer and photographer John Gilbey needed a cheap way of…

Water

An EU project has revealed the extent of river fragmentation…

Mapping

A new, double-sided world map projection seeks to minimise the…

Water

 Water scarcity is predicted to rise – two experts share…

Mountains

New collaborative research from the University of Oxford and the…

Places

Conceived during the late 1800s, Letchworth Garden City was the…

Places

Multiple failed attempts to build on a patch of land…

Deserts

New 'deep learning' technology is helping to identify trees in…

Places

The land around the Kinabatangan River in the state of…

Places

Highlights from the column that keeps you connected with the…

Places

At the end of a perplexing and thought-provoking year, we…

Places

The city of Mosul is slowly putting itself back together…