A recent study on the Earth’s total groundwater suply shows that the total volume of groundwater of any age is about 23 million cubic kilometres. However, less than six percent of the total amount is modern groundwater that is replenished within a human lifetime, the study reveals. Some of the largest volumes of modern groundwater are in the Amazon Basin, the Congo, Indonesia, and in mountain chains like the Rocky Mountains, the least amount is not surprisingly in more arid regions such as the Sahara. The study was conducted by the Universities of Victoria, Calgary (both Canada), Austin (USA/Texas) and Göttingen (Germany) and published in Nature Geoscience.
Groundwater is one of the planet’s most exploited and most precious natural resources. Around the world, there is increasing demand to know how much we have and how long before it is tapped out. “The amount of 23 million cubic kilometers is enough to cover the global land surface in a layer 180 metres deep,” explains Dr. Elco Luijendijk from Göttingen University’s Geoscience Centre. “Although the volume of modern groundwater may appear small at first glance, it is still much larger than all other components of the active hydrological cycle such as water in rivers, lakes, and the atmosphere.”
The study combined measurements of radioactive tritium introduced to the groundwater by nuclear tests in the 1950’s with computer models of groundwater flow in the upper two kilometres of the subsurface. “Knowing the volume of modern groundwater is important because it is a more renewable resource than older stagnant groundwater,” says Dr. Luijendijk. “However, modern groundwater is also more vulnerable to climate change and contamination by human activities.”.
Original publication: Tom Gleeson et al. The global volume and distribution of modern groundwater. Nature Geoscience 2015. Doi: 10.1038/ngeo2590.