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 were 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.”
agriculture The growth of plants, animals or fungi for human needs, including food, fuel, chemicals and medicine.
aquifer Rock that can contain or transmit groundwater.
climate The weather conditions that typically exist in one area, in general, or over a long period.
constant Continuous or uninterrupted. (in mathematics) A number that is known and unchanging, usually based on some mathematical definition. For example, π (pi) is a constant equal to 3.14. . . and defined as the circumference of a circle divided by its diameter.
crop (in agriculture) A type of plant grown intentionally grown and nurtured by farmers, such as corn, coffee or tomatoes. Or the term could apply to the part of the plant harvested and sold by farmers.
current A fluid — such as of water or air — that moves in a recognizable direction. (in electricity) The flow of electricity or the amount of charge moving through some material over a particular period of time.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
ecosystem A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.
freshwater A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.
groundwater Water that is held underground in the soil or in pores and crevices in rock.
habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.
irrigation An engineered supply of water to land or crops to help growth.
model A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes. Or an individual that is meant to display how something would work in or look on others.
sustainable An adjective to describe the use of resources in a such a way that they will continue to be available long into the future.
threshold A lower limit; or the lowest level at which something occurs.
tipping point A point at which some action leads to a disproportionately large or irreversible change in a process, impact or attitude.
watershed A high point in the landscape that marks the dividing line for which lake or ocean or river any flowing water will head toward. For instance, a mountain chain may mark where water on one side drains via rivers into one ocean, and water falling on the other side will drain into a different ocean (via rivers).