PNNL Study Assesses Future of Groundwater

For those of us in the Tri-Cities, the sprinklers watering our lawns and nourishing our crops are primarily fed by surface water from the Columbia River.

Much of the world, however, depends on groundwater from subsurface aquifers to irrigate crops and provide potable drinking water. Understanding the long-term viability of these aquifers is vitally important.

To explore this issue, researchers at the Department of Energy’s Pacific Northwest National Laboratory recently studied the global demand for groundwater. They focused on understanding how groundwater extraction might evolve over the remainder of the century and how the sources of water supply might shift as a result.

In particular, the scientists sought to quantify when, where and why groundwater extraction might peak—and at what cost. While we may not run out of groundwater, it may not be possible to meet growing demand without digging deeper wells or using more costly equipment and more energy to pump it out of the ground.

Given that about a fifth of the world’s food production depends on groundwater, this may lead to higher water and food costs and changes in international agricultural trade.

Using a global model that integrates human activity and Earth systems, scientists simulated groundwater withdrawals across 235 water basins under 900 climate change scenarios. Looking at the results, they found that, despite representing 98% of the Earth’s liquid freshwater, groundwater resources are not without their limits.

As accessible groundwater supplies become increasingly scarce and underground aquifer levels fall, extracting deeper water becomes more difficult and expensive. The study showed that, like minerals and other depletable resources, groundwater behaves as a nonrenewable resource.

As such, it will follow a trend that leads to a peak in extraction and eventual decline in response to rising costs. For groundwater, that may mean a change in how water is managed, where food is produced or which foods are imported and exported.

In nearly all the researchers’ scenarios, groundwater extraction on a global scale is projected to peak around the middle of the century and then decline through 2100. The study suggested that, on average, about one-third of the groundwater basins would see peak-and-decline trends, exposing nearly half of the world’s population to groundwater stress—meaning it is physically or economically infeasible to access the groundwater.

It also showed that withdrawals from as many as 21 basins may already have peaked. These basins are located primarily in countries with the highest extraction rates, including the United States, Mexico, Pakistan, India, China, Saudi Arabia and Iran.

While researchers have not yet fully explored the specific drivers for each basin, the Pacific Northwest appears to be in better shape than some of our neighbors. The models indicate our region’s groundwater is less constrained because agricultural and homeowner demand for groundwater is relatively low due to the availability of surface water from the Columbia River.

Researchers used the Global Change Analysis Model for these studies. Developed by the Joint Global Change Research Institute—a collaboration between PNNL and the University of Maryland—this open-source computer model allowed researchers to explore the interconnections and dependencies among energy, water, land, climate and economics.

As a result, they gained greater insights into the competing interests for water due to human influences than previous studies. Their results can help inform decision-makers about how groundwater withdrawal affects food production, as well as energy demand and the extraction of raw materials. It also can help shape approaches for water management, irrigation modernization and sustainable agriculture.

As Tri-Citians, we likely know someone who spends time adjusting sprinklers to grow enough zucchini for the entire neighborhood.

With studies like these, researchers at PNNL are helping understand the demand for groundwater and the tradeoffs that may affect how global breadbaskets feed the world.

Steven Ashby, director of Pacific Northwest National Laboratory, writes this column monthly. To read previous Director's Columns, please visit our Director's Column Archive.