Groundwater is one of the most exploited – and precious – natural resources on Earth. Now, there’s an increasing demand to know how much is left, and how long before it’s tapped out. For the first time since the 1970s, an international group of hydrologists has produced the first data-driven estimate of our planet’s total supply of groundwater. This study, led by Tom Gleeson of the University of Victoria alongside researchers in Texas, Calgary and Göttingen, was published about a month ago in Nature Geoscience.
The larger part of this study is the “modern” story with groundwater, with the report revealing that less than six percent of groundwater in the upper two kilometers of Earth’s landmass is renewable within a human lifetime. This, Gleeson says, is something that has never before been known. Gleeson warns that humans are using Earth’s groundwater resources much too fast than they’re being renewed, setting the stage for a Malthusian crisis. With a growing global demand for water, especially in light of climate change, this study provides vital information to water managers and policy developers, as well as scientists from such fields as hydrology, atmospheric science, geochemistry and oceanography, all to better manage groundwater resources.
Through numerous datasets and over 40,000 groundwater models, the study estimates a total volume of nearly 23 million cubic kilometers of total underground water, .35 million cubic kilometers of which is younger than 50 years old. Young and old groundwater interact fundamentally differently with the rest of the water and climate cycles. Old groundwater, which is found deeper, is often used for agriculture and industry, and tends to be more salty than ocean water. While the volume of modern groundwater dwarfs all other components of the active water cycle and is a more renewable resource, since it’s closer to surface water and moves faster than old groundwater, it tends to be more vulnerable to climate change and contamination.
The map of the study reveals most modern groundwater in tropical and mountain regions. Some of the largest deposits are located in the Amazon Basin, Congo, Indonesia and along the Rockies in North and Central America. Although high northern latitudes are excluded from the data due to technical restrictions, this area is largely under permafrost to begin with, and has very little groundwater. Not surprisingly, the least amount of groundwater is in more arid regions, such as the Sahara. While there had previously been an intuition that drier areas would have less groundwater than humid areas, this proves that to be true. The next step will be to analyze volumes of groundwater in relation to how much is being used.
If you’d like to learn more about this study, you can click here!