The findings underscore a looming threat to water availability and agricultural sustainability, particularly in regions heavily reliant on groundwater.
In a groundbreaking study published in the journal Nature, researchers from the University of California, Santa Barbara, and ETH Zürich reveal alarming trends in groundwater level depletion, with rates accelerating over the past four decades in nearly one-third of the aquifers studied worldwide. The findings underscore a looming threat to water availability and agricultural sustainability, particularly in regions heavily reliant on groundwater.
The study highlights the intricate relationship between human activities, climate change, and groundwater depletion. Groundwater, traditionally considered a reliable freshwater source in regions with erratic rainfall, is now under duress due to a feedback loop triggered by decades of uncontrolled fossil fuel combustion. This has resulted in more frequent and severe droughts, forcing communities to increasingly depend on groundwater.
California, a major agricultural hub, serves as a poignant example of the consequences of unchecked groundwater use. A decade ago, the state began regulating groundwater after years of over-pumping left over 20 critical groundwater basins, vital for community drinking water systems, in a state of “critical overdraft.”
The study, conducted through the analysis of satellite data and monitoring wells in over 40 countries, reveals that declines in groundwater are most pronounced and accelerating in drier regions with extensive agriculture. Approximately 70 percent of global groundwater withdrawals are attributed to irrigation, and rapidly declining levels were found to be “virtually absent” in uncultivated lands.
However, amidst the concerning trends, the researchers emphasize that long-term groundwater losses are not universal or inevitable. Scott Jasechko, a co-lead on the study, notes, “Rapid and accelerating groundwater declines are, unfortunately, widespread globally. But we also find cases where declining groundwater trends have been reversed following clever interventions.”
In almost half of the cases reviewed, groundwater levels that were declining either slowed (20 percent), reversed (16 percent), or rose (13 percent). Successful interventions involved policies or regulations that shifted to alternative water sources, implemented tiered or higher fees for water consumption, or intentionally replenished aquifers with water from other sources.
The study builds on previous research by the same team, which analyzed the depth of nearly 40 million groundwater wells globally. The researchers found that millions of shallow wells, penetrating just 5 meters into the groundwater, could run dry with modest drops in groundwater levels.
The analysis, based on the largest dataset ever compiled at such a local scale, includes 170,000 wells in nearly 1,700 aquifers worldwide. The results indicate that rapid groundwater level declines of half a meter per year are widespread, posing a significant risk to wells located within five meters of the water table.
Some of the highest rates of groundwater level declines were observed in parts of California’s Central Valley and the adjacent Cuyama Valley, as well as in aquifers in India and other less-studied regions like the West Qazvin plain in Iran.
While the study provides valuable insights, there are acknowledged gaps in global coverage, particularly in parts of China and Africa. Nevertheless, the researchers argue that the detailed, locally relevant information derived from monitoring wells complements satellite-based observations. This combination could pave the way for more effective strategies to address groundwater declines globally.
The urgency of addressing groundwater supply depletion is emphasized by the fact that approximately half of the world’s population, including 145 million Americans, relies on groundwater for drinking water. As climate change exacerbates droughts and extreme weather events, the study underscores the need for proactive measures to safeguard this critical resource and ensure global water security.