How Much of Earth’s Groundwater Do We Have? Study Reveals

Researchers found less than 6% of the groundwater in the upper two kilometres of the planet is renewable in a human lifetime.

Key to determining the age of all this stored water is a collection of thousands of tritium measurements.

And while still dwarfed by the amount of water in the oceans, groundwater accounts for most of the fresh water on the planet.

The team used multiple data sets and more than 40,000 groundwater models to provide a data-driven estimate of the Earth’s total supply of groundwater.

The work is the result of a study carried out by researchers at University of Victoria, University of Texas at Austin, the University of Calgary and the University of Göttingen led by Dr. Tom Gleeson of UoV.

“Groundwater is a super-important resource”, Gleeson said in an interview with CBC News. It can help water managers and policy developers to manage groundwater resources in a better and sustainable way.

A look at previous estimates of total groundwater showed the crude calculations were not far off.

Scientists calculate there are 23 million cubic kilometres of total groundwater, most in underground aquifers, but only.

Any groundwater containing elevated levels of tritium must, they assumed, be “modern” groundwater that entered the ground since nuclear testing began about 50 years ago.

Knowing the difference between modern and older groundwater is really important. They are fundamentally different in how they interact with climate cycles and the rest of the water. Old groundwater is found deeper and is normally used in agriculture and industry. It may sometimes contain uranium or arsenic, and is generally more salty than seawater. “It is a small pool, smaller than I thought, which means that it’s a more finite resource”, says Gleeson. Modern groundwater is closer to the surface and more vulnerable to climate change and contamination from pesticides, detergents and other pollutants.

According to the study’s maps, most modern groundwater is in mountainous and tropical regions.

There is very little modern groundwater to be found in arid regions such as the Sahara but significant supplies of older, less renewable groundwater. Researchers excluded high northern latitudes because satellite data doesn’t accurately cover these latitudes.

‘Now, we have a quantitative estimate that we compared to geochemical observations’.

So, how long do we have?

The next step will be to analyze the volumes of groundwater in relation to how much is being used and depleted.

In a prior study that ultimately lead to the research on modern groundwater, Dr. Gleeson’s 2012 groundwater footprint report (published in Nature) mapped global hotspots of groundwater stress, charting precipitation rates versus rates of use through pumping, mainly for agriculture.

A few of these hot spots are northern India and Pakistan, northern China, Iran, Saudi Arabia, and parts of the USA and Mexico.

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.

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.