Groundwater resources are declining across the globe, dropping in 71% of aquifers, according to a new study in Nature.
Groundwater provides drinking water to billions of people and supplies nearly half of all water used for irrigation, but excessive use has depleted this vital water resource.
The findings provide the most comprehensive analysis of global groundwater levels to date. They indicate that the decline in water resources is especially widespread in dry regions with extensive croplands.
The authors of the new report says the problem is increasing, with groundwater depletion speeding up in 30% of the studied aquifers in the 21st century.
But the study also highlights where efforts to remedy the problem are succeeding.
It focuses on policy changes and improved aquifer management.
“This study was driven by curiosity,” says lead author Debra Perrone, of the University of California, Santa Barbara’s Environmental Studies Program in the US.
“We wanted to better understand the state of global groundwater by wrangling millions of groundwater level measurements.”
Researchers compiled data from national and subnational records to analyse groundwater trends in 170,000 wells to track the changes over time.
They found that accelerated decline is especially prevalent in arid and semi-arid lands with extensive croplands.
“An intuitive finding,” says co-lead author Scott Jasechko, an associate professor in the same school. “But it’s one thing for something to be intuitive. It’s quite another to show that it’s happening with real-world data.”
The findings provide hope in regions where groundwater levels have stabilised or recovered following direct human intervention.
These interventions include policy changes like those in Bangkok, Thailand, where regulations to reduce groundwater pumping reversed the declines of the 1980s and 90s.
Substituting groundwater for another water source has also enabled some aquifers to recover, like in Albuquerque in the US where groundwater levels are recovering following the transfer of surface water.
Lastly, intentionally refilling depleted aquifers has proven successful in Arizona in the US, with water diverted from the Colorado River.
“Groundwater is often viewed as a bank account for water. Intentionally refilling aquifers allows us to store that water until a time of need,” says Jasechko.
Perrone and Jasechko are now looking at how groundwater levels vary over time in the context of climate change. Connecting these rates of change to the depths of actual wells will provide better predictions of where groundwater access is at risk.