Humanity’s thirst for groundwater is threatening natural waterways.
Most of Earth’s freshwater sits underground. Tapping this groundwater has enabled farming in drier places. One example is California’s Central Valley. That’s where about one-fourth of U.S. food comes from. Groundwater is what made this region’s crop production so bountiful.
Worldwide, about 70 percent of the groundwater pumped to the surface goes for farming. But surface waters — rivers and streams — rely on groundwater, too. Pumping large amounts of groundwater over a short period can be harmful. Natural waterways can begin to empty. And that can hurt freshwater ecosystems. Scientists consider this a tipping point. That’s when small actions can begin having unusually big impacts.
A new study has found that 15 to 21 percent of tapped watersheds have reached this sort of tipping point. Most of those tapped rivers and streams are in dry regions. They include parts of Mexico and northern India. Farmers in these areas use groundwater to irrigate their crops. At current pumping rates, the study predicts that 42 to 79 percent of watersheds around the world where groundwater is pumped up for use at the surface will reach tipping points by 2050.
The new study appeared October 3 in Nature.
“It’s really quite alarming,” says Inge de Graaf. As a hydrologist, she studies the distribution and circulation of the Earth’s water. She works at the University of Freiburg in Germany. Groundwater and surface waters are closely linked, she says. “Too much pumping creates a ticking time bomb.”
A healthy groundwater aquifer protects ecosystems against seasonal ups and downs in the availability of water. That provides stability for area plants and animals. But if too much groundwater is pumped up from below, surface waters will begin to drain into the aquifer. And that can harm what is living in rivers and streams.
De Graaf and the study team created a computer model. It linked groundwater pumping and water flows within rivers. The model covered five decades, from 1960 to 2010. Then the researchers used climate forecasts to help the model predict what might happen in future years. Throughout, they kept groundwater pumping rates constant. More than half of pumped watersheds are likely to cross this ecological threshold before 2050, the model finds.
“We need to be thinking about this now, not in 10 years,” de Graaf says. “Our study shows us where to target more sustainable efforts.”