Groundwater remains a crucial source of fresh water for farming, everyday use, and broader industry. Yet these groundwater resources face increasing pressure from climate change and overuse, posing risks to economies and ecosystems alike.
Researchers from the University of California, Santa Barbara, published a landmark assessment in Nature that examines groundwater levels across the globe. The study analyzed about 1,700 aquifers and highlights the value of combining satellite-derived storage trends with in situ measurements from monitoring wells. This dual approach gives policymakers a clearer view of how groundwater resources are changing worldwide.
The primary finding is sobering: groundwater resources are generally diminishing. The study notes a decline exceeding 0.5 meters per year in the 21st century, affecting roughly 71% of the aquifers examined. Yet the research also points to promising management strategies and ways to mitigate declines.
The global trend shows a reduction in groundwater resources, with declines of more than 0.5 meters per year during the 21st century
Groundwater depletion can disrupt water systems in many ways. Pumping wells may struggle to bring water to the surface, potentially leading to drying wells. Excessive extraction can cause seawater intrusion and degrade water quality. Because groundwater and surface water systems are often connected, heavy pumping can reduce river flows as well. These dynamics were explained by Debra Perrone, associate professor in the Environmental Studies Program at UCSB, who emphasized the interconnected nature of water sources in a discussion with SINC.
The headline results were published in 2021, with subsequent work including studies on constructed wells that monitor groundwater flow. Perrone notes that monitoring wells reveal information about water supply, while groundwater wells illuminate demand, underscoring the importance of comprehensive measurement in water resource planning.
Greater impacts in dry regions
To build a global picture, researchers gathered data from national and local registries and multiple institutions. The project took three years, with two years spent cleaning and classifying data. They highlight that meaningful insights come from large datasets, citing hundreds of millions of water level measurements taken from tens of thousands of wells over the last century.
After translating these measurements into trend analyses, the team reviewed more than 1,200 publications and mapped aquifer boundaries within study areas. In total, 1,693 aquifer systems were identified worldwide. Findings show that 36% of aquifers are decreasing at about 0.1 meter per year, while 12% are dropping faster than 0.5 meters per year. When compared with depletion data from 1980 to 2000, roughly 30% of studied aquifers face rapid depletion in the 21st century, a pattern especially evident in arid and semi-arid regions.
The deepening declines are more common in dry climates, and the rate of decrease is typically higher in arid agricultural zones. This intuitive pattern is supported by real-world data, as noted by Scott Jasechko, co-senior author and professor at the Bren School of Environmental Science and Management at UCSB.
Yet data alone do not tell the whole story. Perrone cautions that water is essential for drinking, farming, and industrial activity. Groundwater offers a reliable, year-round resource that can buffer droughts when rainfall is scarce. Overexploitation could leave key sectors without adequate supply during shortages.
Reasons for cautious optimism
The study also identifies positive signs: about 6% of aquifers show gains of around 0.1 meter per year, and 1% rise by 0.5 meter per year. These increases may reflect successful depletion controls, surface water transfers, or land management and recharge projects. Jasechko stresses that deliberate, sustained effort can change outcomes.
An example of positive work is in Tucson, Arizona, where Colorado River water is deliberately allocated to recharge the Avra Valley aquifer. This practice stores water for later use. Jasechko notes that groundwater is often viewed as a financial resource, and intentional recharge can help build resilience, though river ecosystems may respond to altered flows. The Colorado River’sDelta and downstream water delivery have already experienced changes as a result.
Perrone emphasizes cautious optimism: more than 100 aquifers have shown slowed decline, halted, or even reversed trends. Still, the rate of rise often trails the rate of decline, making gains harder to sustain. Beyond storage, restoring balance can also benefit regional ecosystems. In a 2014 project, Perrone highlighted that aquifer recharge can store six times more water per dollar than surface reservoirs, and reducing demand remains a key strategy.
The team now focuses on how groundwater levels evolve over time in the context of climate change. Linking rates of change to actual well depths will improve estimates of where access is at risk and guide adaptive management strategies.
Reference work: Nature, 2023 edition on global groundwater depletion and management. [Citation: Nature 2023, cited by the UCSB research team]
Notes and ongoing inquiries continue to shape this field and support more resilient water futures across regions facing water stress.