The human population currently has a water footprint 3.5 times the amount of groundwater available and are overexploiting resources critical to agriculture, according to new research.

While previous assessments of global water resources have focused on surface water, it remains unclear how groundwater depletion compares to the rate of natural renewal.

Research published in science journal nature by Tom Gleeson of McGill University in Montreal estimated that the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers.

It said that about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat.

Furthermore, research reported that 80% of aquifers have a groundwater footprint that is less than their area, meaning that the net global value is driven by a few heavily overexploited aquifers.

The groundwater footprint is the first tool suitable for consistently evaluating the use, renewal and ecosystem requirements of groundwater at an aquifer scale. It can be combined with the water footprint and virtual water calculations, and be used to assess the potential for increasing agricultural yields with renewable groundwater.

The method could be modified to evaluate other resources with renewal rates that are slow and spatially heterogeneous, such as fisheries, forestry or soil, according to the findings.