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It would be an insidious route to the end of the world, one that doesn't make quite the exciting movie plot as asteroids and super tornadoes but that could be far more of an effective apocalypse: Water overuse.
There are nearly 7 billion people on the Earth at this moment, and each person depends on water as a basic requirement for survival. Surface waters, such as rivers and ponds, cannot provide enough water to support society, especially the demands of developed nations, making aquifers-deep caverns of underground water the size of several states, at the least - a vital source of water.
In many parts of the world, civilization is unknowingly sucking these aquifers dry.
Dan Charles, National Public Radio's food and agriculture correspondent, reports that among the world's most important aquifers, those experiencing the most stress are in Western Mexico, the Middle East, India-Pakistan, Northern China, and the High Plains of the United States. And, he says, the primary threat is agriculture pulling out water faster than is being naturally replenished.
"Some of these aquifers are being exploited at a stunning rate, but what's truly alarming is how many people depend on that over-exploitation for their food," Charles said.
He explained what he called each aquifer's footprint, an area of land many times larger than the actual aquifer that relies on the underground resources. For example, huge population densities rely the food grown in India and North China, not to mention Mexico's U.S.-bound fruit and vegetable production and the United States' Great Plains grain belts that "feed the world."
The Ogallala Aquifer, which sits underneath portions of eight states including South Dakota and Nebraska, is the U.S. aquifer that Charles mentions. He stresses that this year's historic drought is definitely playing a part in the Ogallala's failing health, but ultimately, the demand by irrigation needs is the ongoing threat.
"The High Plains [Ogallala] aquifer in the United States, meanwhile, is having a particularly bad year," Charles said. "Farmers are pumping even more than usual, because of the drought afflicting this part of the country, and it is getting less replenishment from rainfall. So, water levels in the aquifer are falling even faster, leaving less water for the region's rivers, birds, and fish."
The Ogallala is approximately 174,000 square miles in size and a depth of a few hundred feet to, at most, 1000 feet depending on the location, according to the High Plains Underground Water Conservation District No. 1, based in Lubbock, Texas. Some wells drilled into this aquifer yield more than 1000 gallons of water per minute, while wells in others yield only a couple of gallons per minute. Depth to water below the land surface ranges from just 100 to nearly 400 feet, adds the Northern Plains Groundwater Conservation District, based in Dumas, Texas.
The Ogallala is shrinking. In 1990, it contained 3.27 billion acre-feet of water, the majority of which was located under Nebraska. The most recent estimate of the volume of water in the entire aquifer was just under 3 billion acre-feet, reports the High Plains Underground Water Conservation District. It takes an estimated 50 years to recharge lost water to the aquifer. Natural recharge happens through percolation of precipitation through the soil into the water table. The average recharge rate for the entire Ogallala Aquifer is estimated at one-half inch per year and brings with it chemicals leached from agricultural ground.
Before the development of irrigation, discharge from the aquifer occurred from natural resources such as ponds, lakes, streams, and wetlands fed by seeps and springs. The High Plains Underground Water Conservation District reports that while there are still seeps and springs flowing, many have ceased because of the lowering of the water table. About 95 percent of the water pumped from the Ogallala is for crop irrigation. According to the U.S. Geological Survey, a study from 2000 found that irrigation withdrawals from the Ogallala totaled 17 billion gallons per day. It's no wonder that in the last 50 years, the water table has dropped 190 feet in depth, reports the Environmental Defense Fund, headquartered in New York City with offices across the country.
The Ogallala Aquifer isn't going to dry up in the immediate future, but it's also not an infinite resource. The Environmental Defense Fund estimates the aquifer's lifespan range from 60 to 250 years, depending on the area and the rate of annual water use and weather conditions. Certainly, drought conditions like that of this year-the U.S. Drought Monitor continues to show much of the area covering the region of the Ogallala Aquifer sitting in an exceptional drought with long-range conditions continuing to worsen-deplete the aquifer at an even faster rate. In addition to crop irrigation-a 2003 study found that 1 bushel of corn required 2100 gallons of irrigated water-the Environmental Defense Fund reports that a significant amount of water usage also goes toward the making of corn ethanol, to the tune of an additional 780 gallons of water to produce 1 gallon of ethanol.
Of course, water is also being pumped from the aquifer for non-agricultural uses, including home use, golf course and green space irrigation, and industrial needs.
Many producers complain about water use restrictions, but before the government intervened, prior to the 1970s, farmers were lowering the water table by as much as five feet in their areas each year, according to the High Plains Underground Water Conservation, and that was well before the crop production levels of today. Still, despite water use regulations, the water table continues to drop, simply because supply can't keep up with demand, Charles reports.
"This can't go on forever. Already, many farmers are being forced to dig deeper wells to get at that water," he said. "In some areas, they'll just have to stop using those underground stores of water altogether."
But there's hope. Here's what's happening in water conservation trends:
· Irrigation technologies that use water more efficiently, adjusting irrigation schedules to local weather conditions and soil moisture results, as well as regulating water pressure to reduce waste through runoff or evaporation.
· New drought-resistant crop varieties, such as Monsanto's DroughtGard corn and DuPont Pioneer's AQUAmax corn.
· More federal incentives to encourage farmers to use less water, such as through no-till cropping systems, crop rotation, and precision nitrogen applications.