A recent review study led by the University of Texas at Austin provides an overview of the planet’s freshwater supply and strategies for managing it sustainably.
Posted in Nature Reviews Earth and the environmentThe study highlights the links between surface and groundwater and calls for diverse strategies to manage both.
“I like to stress a lot of the solutions and how they can be improved,” said lead author Bridget Scanlon, a senior investigator with the UT Bureau of Economic Geology, a research unit in the Jackson School of Geosciences.
The study draws on data from satellites, climate models, observational networks and nearly 200 scientific papers to analyze Earth’s water supplies, how they change in different regions and what drives those changes. The study co-authors include nearly two dozen water experts from around the world.
According to research, humans depend primarily on surface water. Globally, it accounts for 75% of irrigation and 83% of municipal and industrial supplies annually. However, what we see on the surface is tightly connected to the groundwater flow. In the United States, about 50% of a stream’s annual flow begins as groundwater. Globally, surface water that seeps into the ground makes up about 30% of the annual groundwater supply.
Human intervention can strongly affect the exchange of water between surface and groundwater sources. About 85% of the groundwater pumped by humans in the United States is considered to be “taken” from surface water, which results in reduced streamflow. At the same time, irrigation obtained from surface water can increase groundwater recharge as irrigated water seeps through the ground into aquifers.
The study cites many examples of human activity affecting this flow between surface water and groundwater supplies. For example, surface irrigation water fed aquifers in the early to mid-20th century in the US Northwest Columbia Plateau and the Snake River Plain, while global models show that groundwater pumping has greatly reduced the volume of water going into streams, by 15- 21% of global watersheds are at risk due to reduced flows.
Despite their inherent connection, surface and groundwater are often organized and managed as separate sources. According to the researchers, water’s future resilience depends on realizing that surface water and groundwater act as a single resource — and acting on that knowledge.
The study describes different approaches to managing water through natural and engineering solutions that can help increase water supply, reduce demand, and store and transport water. According to Scanlon, one of the best ways to adapt to increased climate variability is to store water during wet times and draw from it during times of drought.
“We are suffering from drought and floods,” she said. “We’re trying to manage these extremes and the way to do that is to stock up on water.”
Annually, the world stores about 7,000-8,300 cubic km, or roughly two quarts of Lake Michigan water, in surface reservoirs. It’s important to continue to develop groundwater supplies as well, the researchers said, because they are more resilient than surface aquifers during long-term droughts. Managed aquifer recharge can help cities build up their groundwater supplies by collecting surface water and diverting it underground to aquifers. Globally, about 10,000 cubic km of water is stored in this way each year.
“This kind of integrated research, linking surface and groundwater, is exactly what we need to develop lasting solutions to issues like freshwater use,” said Scott Tinker, director of the Office of Economic Geology. “Studies are often done in isolation, and well-intentioned applications have unintended consequences.”
Matthew Rudel, a hydrologist at NASA’s Goddard Space Flight Center who was not involved in the study, said the paper provides a useful compendium of research findings and potential solutions for managing water supplies while also preserving water quality — a difficult-to-quantify characteristic. Remote monitoring of the quantity – in mind.
“Water quality is one of the next goals in terms of the ability to manage water resources,” he said. “I love that this is incorporated, too.”