Humankind’s collective thirst is slowly desiccating landscapes worldwide, a study of groundwater finds.
Water stored in aquifers underground makes up the vast majority of accessible freshwater on Earth. Its abundance has fueled forays into drier locales, such as California’s Central Valley, enabling a boom in crop production (SN: 7/23/19). And overall, about 70 percent of the groundwater being used worldwide goes to agriculture. But surface waters — rivers and streams — rely on groundwater, too. When people pump too much too quickly, natural waterways begin to empty, compromising freshwater ecosystems.
A study in the Oct. 3 Nature finds that this ecological tipping point, what scientists call the environmental flow limit, has already been reached in 15 to 21 percent of watersheds tapped by humans. Most of those rivers and streams are in drier regions like parts of Mexico and northern India where groundwater is used for irrigation.
If pumping continues at current rates, the authors estimate that by 2050, anywhere from 42 to 79 percent of pumped watersheds will have crossed this threshold.
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“It’s really quite alarming,” says Inge de Graaf, a hydrologist at the University of Freiburg in Germany. “Groundwater and surface waters are intimately connected, and too much pumping creates a ticking time bomb.”
A healthy aquifer buttresses ecosystems against seasonal fluctuations in water availability, providing stability for resident plants and animals. But if too much groundwater is pumped, surface waters begin to seep into the aquifer, draining the life from many river and stream habitats.
De Graaf and colleagues created a statistical model that linked groundwater pumping with groundwater flow to rivers from 1960 to 2100. Projecting into the future, the researchers tweaked the model based on different climate projections, but kept groundwater pumping rates constant. The team found that more than half of watersheds where pumping occurs will likely cross this ecological threshold before 2050.
“We need to be thinking about this now, not in 10 years,” de Graaf says. “We can decrease pumping in these areas, develop better irrigation…. Our study shows us where to target more sustainable efforts.”