A recent study in Nature highlights the unsustainability of withdrawals from underground aquifers in the world's most populated areas.
Here we define the groundwater footprint (the area required to sustain groundwater use and groundwater-dependent ecosystem services) and show that humans are overexploiting groundwater in many large aquifers that are critical to agriculture, especially in Asia and North America.
We estimate that the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers and that about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat.
That said, 80 per cent of aquifers have a groundwater footprint that is less than their area, meaning that the net global value is driven by a few heavily overexploited aquifers. The groundwater footprint is the first tool suitable for consistently evaluating the use, renewal and ecosystem requirements of groundwater at an aquifer scale. It can be combined with the water footprint and virtual water calculations, and be used to assess the potential for increasing agricultural yields with renewable groundwater. The method could be modified to evaluate other resources with renewal rates that are slow and spatially heterogeneous, such as fisheries, forestry or soil.
A Nature news story Demand for water outstrips supply accompanied the research paper.
Across the world, human civilizations depend largely on tapping vast reservoirs of water that have been stored for up to thousands of years in sand, clay and rock deep underground. These massive aquifers — which in some cases stretch across multiple states and country borders — provide water for drinking and crop irrigation, as well as to support ecosystems such as forests and fisheries.
Yet in most of the world’s major agricultural regions, including the Central Valley in California, the Nile delta region of Egypt, and the Upper Ganges in India and Pakistan, demand exceeds these reservoirs' capacity for renewal...
“This overuse can lead to decreased groundwater availability for both drinking water and growing food,” says Tom Gleeson, a hydrogeologist at McGill University in Montreal, Quebec, and lead author of the study. Eventually, he adds, it “can lead to dried up streams and ecological impacts”...
But Gleeson adds that there is at least one significant source of hope. As much as 99% of the fresh, unfrozen water on the planet is groundwater. “It’s this huge reservoir that we have the potential to manage sustainably,” he says. “If we choose to.”
There's hope — if we "choose" to manage the aquifers. We certainly haven't seen many wise "choices" up to now, have we?
When climate-induced droughts occur, as in the United States this year, withdrawals increase to support agriculture. The Lubbock (Texas) Avalanche Journal reports that Drought hits Texas part of Ogallala aquifer (July 4, 2012).
The historic Texas drought caused the Ogallala Aquifer to experience its largest decline in 25 years across a large swath of the Texas Panhandle, new numbers from a water district show.
The 16-county High Plains Underground Water Conservation District reported this week that its monitoring wells showed an average decline last year of 2.56 feet — the third-largest in the district’s 61-year history, and three times the average rate over the past decade. Farmers pumped more water during the drought to compensate for the lack of rainfall, which was about two-thirds less than normal last year in Lubbock and Amarillo.
Farther north in the Panhandle, along the state’s border with Oklahoma, a second water district also registered large declines in the Ogallala. Steve Walthour, the general manager of the eight-county North Plains Groundwater Conservation District, calculated on Monday that the average drop in the Ogallala reached 2.9 feet last year.
“We’ve seen some pretty heavy declines,” Walthour said, noting that the west side of his district got hit especially hard.
Given the catastrophic nature of the drought, which was the most intense in recorded state history, some farmers said things could have been worse.
“You never want to pull that much down, but under the circumstances I think we’re probably coming out pretty well,” said Tommy Fondren, who rents out his land in Crosby County for cotton farming.
You never want to pull that much down, but under the circumstances I think we're probably coming out pretty well, said cotton farmer Tommy Fondren. Hmmm...