We are sucking the world’s ancient freshwater stores faster than they can be replenished
Across the globe, human civilizations depends on mining the vast reservoirs of freshwater that have accrued deep underground through millennia. Stretching underneath national borders, these “fossil” aquifers sustain us and our industries, and influence the health of many ecosystems. The aquifers account for 99 percent of our world’s unfrozen freshwater supply. We are now depleting them faster than they can be replenished. In the process, we are reshaping not just the surface of Earth but the subsurface as well.
“Humans are overexploiting groundwater in many large aquifers that are critical to agriculture, especially in Asia and North America,” says a recent analysis of the world’s groundwater footprint published in the journal Nature. Water withdrawals in American Great Plains, the Upper Ganges region in India and Pakistan, the Nile Delta region, and parts of China, Iran, and Mexico are exceeding underground reservoirs’ capacity for renewal, the report says. Together, these areas support one quarter of the world’s population
These regions also happen to be among the world’s most vital agricultural zones, and researchers say agriculture is largely to blame for the looming water crisis people in these regions face.
According to UNESCO estimates, groundwater use has tripled in the last 50 years, with India’s usage growing most rapidly. Between 2002 and 2008, more than 26 cubic miles of groundwater disappeared from the Indus River plain aquifer. Researchers say the reservoir would require 54 times as much rainfall as it now receives to replenish the water that has been taken out.
In central Saudi Arabia, fossil water remained sealed underground while local populations adapted to desert conditions. But now these ancient water stores are being tapped in areas that never before supported agriculture. In Australia, the Great Artesian Basin, the largest aquifer in the world, provides most of the country’s inland with its only reliable source of freshwater. It is being depleted not only through agricultural uses, but also through illegal bores and open-earth drains. Because the desert area has very low rainfall, the aquifers there don’t get recharged. Once they are drained, they are gone.
In the United States, aquifers have become more important as monoculture agriculture expands and droughts occur more frequently. The vast Ogallala Aquifer, stretching from South Dakota to Texas, provides nearly 30 percent of the nation’s freshwater used for irrigation. But it’s being depleted by as much as two feet each year in some counties. Scientists estimate we would need 6,000 years of uninterrupted rainfall to refill it.
Because most of the extracted groundwater eventually winds up in the oceans and seas, hydrologists have found that groundwater use causes an annual sea-level rise of 0.3 mm. This accounts for nearly a quarter of the total annual sea-level rise that is also perpetuated by global warming. In some low-lying coastal areas, like the Bengal and Mississippi deltas, aquifers will likely be inundated by seawater and ruined.
The controversial natural gas extraction process of hydraulic fracturing that requires millions of gallons of water per drilling well also has a huge impact on our freshwater reserves. A 2011 EPA report estimated that 70 to 140 billion gallons of water are used to fracture 35,000 wells in the US every year. That’s the annual water consumption of 40 to 80 cities each with a population of 50,000, according to the mining watchdog group Earthworks.
Drawing too much water from aquifers also impacts rivers, wells, and wetlands connected to them because depleted aquifers tend to suck in water from these surface water sources. Which means they can dry up streams and rivers and reduce wildlife habitat.
As the world’s population continues to grow, the need for freshwater to produce food and sustain humankind is only going to rise. The challenge now is to figure out ways to feed the world and at the same time manage our freshwater resources so that we aren’t left depending on the uncertain rainfall patterns of our changing climate.