Groundwater levels are plummeting around the world
Envision the global water crisis. You, like many, might picture a parched stream, a dried lake bed, a fallow field. Now try to visualize the ground under your feet and the freshwater stored in between grains of sediment or cracks in rock. Though it may be difficult to visualize, groundwater is vital to humans and ecosystems, and its depletion threatens global freshwater access for humans and nonhumans alike.
Groundwater provides drinking water to billions of individuals. And because groundwater is the primary water source for nearly half of global irrigation, groundwater depletion jeopardizes food production. Groundwater also supports plants and animals near springs, rivers, and wetlands, providing essential ecosystem services.
Over the past six years, we have compiled millions of observations of the depth of groundwater in wells located in more than 40 countries around the globe. From this, we mapped how groundwater levels are changing over time. What we found is concerning.
Groundwater levels are plummeting at rates of several feet per year in many of the world’s aquifers. The most likely driver of rapid groundwater depletion is unsustainable groundwater pumping. Rates of groundwater depletion are accelerating in nearly a third of the global aquifers, posing a major problem. And this problem is getting worse — faster than ever before — in many places, leading to a number of undesirable outcomes.
Groundwater depletion can diminish river flows because of the interconnectedness of groundwater and surface water resources. Groundwater is pumped to support many sectors, including agriculture and industry. Excessive groundwater pumping can cause rivers to leak through their riverbeds into the ground, reducing the amount of water available to ecosystems and downstream communities.
Pumping groundwater can cause land to sink, a process known as subsidence. In coastal areas, seawater inundation is likely to worsen because land is sinking due to groundwater pumping. A recent article in The New York Times profiled a study that found that parts of Boston have been sinking by as much as 3.8 centimeters per decade and may sink by nearly 10 centimeters — about 4 inches — by 2050. Rising sea levels due to global warming are making the problem worse.
The confluence of rising sea levels and sinking land is creating a perfect storm for coastal flooding. Much of the groundwater that is depleted from aquifers moves into other areas of the planet; in fact, depleted groundwater that ends up in the ocean is one of the drivers of global sea level rise, as groundwater depletion transfers water from the continents to the seas. This sea level rise can, in turn, cause coastal aquifers to be contaminated by saltwater, a process known as seawater intrusion.
When groundwater levels decline, wells can run dry, leaving households and farms without water. This is a major issue in many parts of the world, including California’s Central Valley. Generally speaking, household wells are much shallower than irrigation wells in the Valley. This means that wells used to access potable water for household use are at greater risk from depletion than wells used for irrigation. Household wells in the Central Valley tend to be used in rural, agricultural regions where connections to public water systems are not readily available. New, deeper groundwater wells can cost up to $100,000. Because of this large economic burden on households, some rely on stopgaps such as purchasing bottled water.
So what can be done to solve groundwater depletion?
Before we can identify solutions we must understand where groundwater is being depleted. Our latest work did this for dozens of countries where data were available. The most worrisome cases of groundwater decline include aquifers across the western United States, Chile, Morocco, Spain, Turkey, Saudi Arabia, Iran, Afghanistan, India, and China. Rapid declines are nearly always located where the climate is dry and where large swaths of land are used to grow crops. Irrigated agriculture is the world’s largest consumer of groundwater and can deplete groundwater stocks. To address global groundwater depletion, we must focus efforts on the places where conditions are most dire: places where the climate is dry and land is used to grow crops.
But simply mapping the prevalence of groundwater problems does little to address them. That’s why we have also focused our latest research on documenting success stories. The bad news: Success stories are rare. The good news: These rare cases demonstrate that the groundwater problem is fixable and provide instructive examples of how we can make things better elsewhere. Here are a few of the ways that local water managers have worked with engineers and communities to ameliorate groundwater depletion.
One option is to implement existing policies or create new ones. In 1999, new legislation empowered Groundwater Conservation Boards in Arkansas to charge a fee to pump groundwater. Funds accrued from the fee helped to pay for a pipeline to tap water from a large river and move the water to El Dorado, Ark., where groundwater levels had been declining for decades. With newfound access to an alternate water supply, the need for groundwater declined and the aquifer started to recover.
A second option is to access a new water supply. In 2008, the city of Albuquerque increased its use of surface water and reduced its reliance on groundwater. This newfound surface water became available via an engineering project that transfers water from the Colorado River Basin into the Rio Grande. More surface water became available in the Rio Grande for Albuquerque but at the expense of water availability in the Colorado River, which is used so intensively that it rarely reaches the sea. In some ways, this “solution” robs Peter to pay Paul.
A third option is to build large, intentionally leaky “lakes” that act to replenish groundwater. These areas, often referred to as managed aquifer recharge projects, can refill depleted aquifers and have done so in the Avra Valley, located about 20 miles west of Tucson. Notably, the water used to fill these leaky lakes comes from the Colorado River, highlighting that solving a local problem can sometimes come at the expense of neighboring regions.
There are still other options. Desalination has been applied successfully in several areas, though it tends to require considerable energy and can have negative impacts on marine ecosystems. Municipal water recycling in large cities can serve as a new water source, too. No one strategy is optimal everywhere. Finding solutions requires us to understand the local context of both water supply and water demand. The rare good news cases demonstrate the breadth of currently available solutions and the importance of identifying and implementing strategies that are locally relevant.
So, what do these good news cases have in common? Successful solutions require cultivating conversations among stakeholders, finding shared values, and then bringing in objective experts who can help evaluate and implement plans that are of sufficient scale and scope to address the root cause of the problem. Only then can we find local-scale solutions for individual aquifers around the globe.
Solving groundwater depletion is in everyone’s interest. Our work has demonstrated the tremendous scope of this problem and provided examples of ways that it has been addressed. As groundwater depletion accelerates, humanity must accelerate our willingness to find and implement solutions to address global groundwater depletion.
Scott Jasechko is an associate professor of water resources with the Bren School of Environmental Science
Management and Debra Perrone is an associate professor with the Environmental Studies Program at the University of California, Santa Barbara.