A new study has, for the first time, estimated the total volume of groundwater present on the Earth. The results show that we're using up the water supply quicker than it can be naturally replaced, while future research will seek to determine exactly how long it will be until modern groundwater runs dry.
Groundwater is an extremely precious resource, being a key source of sustenance for humanity and the ecosystems we inhabit. It resides beneath the Earth's surface, ranges from millions of years to just months old, and exists in huge quantities – quite literally millions of cubic kilometers. While calculations back in the 1970s roughly estimated the global volume of groundwater, this new study represents the first detailed calculation of the exact quantity, and it could have big implications.
Researchers from the University of Victoria, the University of Texas at Austin, the University of Calgary and the University of Göttingen created a map of groundwater distribution by carefully analyzing numerous datasets, and making use of more than 40,000 scientific models. In all, the study estimates a total volume of almost 23 million cubic kilometers (5.5 million cubic miles) of groundwater.
Two kinds of groundwater were detailed – old and modern. Old groundwater is located deep in the Earth, is salty and often contains uranium or arsenic. In contrast, modern groundwater is closer to the surface, and moves more quickly. Unfortunately, it's also far more susceptible to climate change than the deeper, ancient water.
The map shows the majority of the modern supply to be located in mountainous and tropical regions, such as the Amazon Basin, the Congo and the Rockies. Unsurprisingly, very little groundwater was detected in arid regions like the Sahara desert and Central Australia, which is something that has long been suspected.
"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," said team member Dr Kevin Befus. "Now, we have a quantitative estimate that we compared to geochemical observations."
Of the calculated 23 million km3 of groundwater, 350,000 km3 (84,000 mi3) of it is less than 50 years old. Futhermore, the study found that less than six percent of the groundwater located up to two kilometers (1.2 mi) deep in the earth is renewable within a single human lifetime. In essence, we're using up groundwater far quicker than it can be replaced.
Moving forward, the team plans to further analyze the data with the goal of furthering our understanding of exactly how quickly the modern and old groundwater is being depleted by human activity. Once those calculations are complete, we'll have a strong idea of exactly how long we have before the supply runs out.
In the meantime, the researchers believe that the results of the study will help inform various studies and individuals, from policy developers and water managers to scientists focusing on geochemistry, oceanography and more.
The researchers published the findings in the journal Nature Geoscience.
Source: University of Victoria