New study indicates scientists may be underestimating groundwater’s importance in sustaining streams and plant life.

Groundwater depletion threatens water security in many areas – human activities such as gas drilling and fracking adversely impact surface-water and ground water resources, including sources of drinking water, and can harm aquatic life.

Most of the world’s liquid freshwater supply comes from groundwater. These underground reservoirs of water—which are stored in soil and aquifers—feed streams, sustain agricultural lands, and provide drinking water to hundreds of millions of people.

A new study by Berghuijs et al. published in Geophysical Research Letters found that groundwater replenish rates might be more than previously thought.

The research team produced a model of groundwater replenishment using a recent global synthesis of regional groundwater measurements. They found that climate aridity accurately estimated how much precipitation trickled into groundwater across the globe: arid locations had lower replenishment rates than humid ones. The aridity-based model results closely mirrored field measurements and indicated that previous models underestimated replenishment rates.

This finding has implications for the water cycle – groundwater contributes more to river flow and plant water use than previous models predicted. The groundwater in underground aquifers is one of our most indispensable natural resources, but overuse and contamination from human activities are severely endangering aquifer viability, leading to economic troubles, public health ills, and even water conflict. Once an aquifer is depleted, the ground above it tends to subside into the empty space and closes off the aquifer forever. Right now, human activities are draining aquifers far faster than natural systems can replenish them.

Researchers are now keen to understand how quickly surface water replenishes groundwater stores.