The first data-driven map shows how much groundwater is stored beneath the Earth's surface.
The water underneath the Earth’s surface is a precious natural resource and billions of people around the world rely on it for their daily water use.
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Surprisingly, science does not have sufficient information about the water that has been stored beneath the Earth’s surface or what we know as groundwater.
Back in 1970s, a team of scientists estimated the total supply of groundwater but no calculations were made after that until recently.
The latest research by a team of international hydrologists sheds light on how much water we have and how faster it will run out.
Using multiple datasets and more than 40,000 groundwater models, scientists have mapped out that Earth has a total volume of nearly 23 million cubic kilometres of total groundwater. Of which only 0.35 million cubic kilometres is considered ‘modern’ water.
Knowing the difference between modern and older groundwater is really important. Older groundwater is found deeper, it’s a bit salty and sometimes contains arsenic or uranium. It is mostly used for agriculture and industry.
Young or modern water, on the other hand, is a renewable water source and is closer to the surface. The study suggests that less than 6% of groundwater in the upper two kilometres of the Earth's landmass is renewable within a human lifetime.
"This has never been known before," said lead author Tom Gleeson from University of Victoria. "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."
The map shows that most of the modern water is located in tropical and mountain regions. Some of the largest deposits are in Amazon, Congo, Indonesia, and in Central and North America. The least amount of groundwater was obviously found in barren regions like the Sahara.
This first data driven map is important especially in the context of climate change when the global demand for water is increasing. It can help water managers and policy developers to manage groundwater resources in a better and sustainable way.
“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. Now, we have a quantitative estimate that we compared to geochemical observations.” Dr. Kevin Befus, postdoctoral at University of Texas, and co-author of the study said.
The next step will be to analyze the volumes of groundwater in relation to how much is being used and depleted.
“Since we know how much groundwater is being depleted and how much there is, we will be able to estimate how long until we run out.” Gleeson said.
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The study was published in Nature.