The map above (click to enlarge) is the first-ever global survey of Earth's permeability: essentially, how leaky it is. It shows how easily water passes through surface rocks, which will help us understand the planet's water cycle and predict the sustainability of underground water sources.
Crucially, it could help reveal the hidden underground movements of 99 per cent of unfrozen fresh water - water which is not taken into account in computer models used to predict the climate.
The map was put together by Tom Gleeson of the University of British Columbia in Vancouver, Canada, and his colleagues. They assembled data on the kinds of rocks found in different regions, and, using information on how permeable each type of rock is, calculated how leaky different regions are.
Permeability varies over 13 orders of magnitude, so the figures are not very precise, but they offer a rough picture. Gleeson says the map should help hydrologists to work out how much groundwater moves from one basin or aquifer to another, which is important if the water is to be managed sustainably.
At the moment we don't know how much water is hiding underground, or where it is. As a result, groundwater gets left out of climate models. Gleeson says that is a significant omission, as the movements of groundwater could well affect regional climate:
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