Follow Highway 70 through central Kansas on a hot summer's day and you'll invariably see this: a flat sea of cornstalks, stretching from horizon to horizon as far as the eye can see.

It was not always so. The High Plains region of the United States -- a subregion of the Great Plains stretching from the Midwest to the Rockies -- encompasses some of the most productive agricultural land in the country, but 200 years ago it was arid grassland. Its transformation was accomplished through innovations in technology and relied on a finite resource -- water.

Farmers withstood the High Plains' frequent droughts and dry spells by pumping groundwater from the region's aquifers, a trend that accelerated sharply with the electrification of rural America in the early 20th century. Since then, the levels of those aquifers have been dropping at an accelerating pace.

The recent drought that has gripped much of the Southwest for almost three years has thrown the issue into stark relief. A number of states and the U.S. Geological Survey have issued reports in recent weeks highlighting sharp drops in regional water levels due to increased groundwater pumping.

"The past year, we've had just about the biggest drop in groundwater levels I can remember," said Janie Hopkins, manager of the groundwater division of the Texas Water Development Board.

A recent study by the board found that water levels declined a median total of 4.8 feet between 2010 and 2011, nearly three times higher than the median decline of 2009 to 2010. Considering that the drought is ongoing in many of the districts, water managers fear the findings for 2012 and perhaps even 2013 will be similarly severe.

An accelerating rate of decline
The nation's largest aquifer is the Ogallala, underlying more than 170,000 square miles of the High Plains region and stretching across eight states, from Nebraska to Texas. A major source of both irrigation and domestic consumption, it is also one of the fastest-declining groundwater reserves in the country.

A recent study by USGS found that its rate of depletion accelerated sharply over the past decade with declines from 2001 to 2008 accounting for 32 percent of the cumulative depletion over the course of the entire 20th century. In places, water table levels have fallen 160 feet since the mid-20th century.

"During the 1940s and 1950s, the growth of populations and the expansion of industry meant many more farmers were drilling wells, particularly in the High Plains," said Leonard Konikow, a research hydrologist with USGS. "This was land that had never been irrigated before -- land that ordinarily wouldn't have supported these kinds of crops."

While aquifers do recharge over time -- the nation's water tables kept to a relatively constant level during the historically wet, cool years of the 1960s and 1970s -- that rate of recharge can't make up for water use in the West.

The Ogallala aquifer is the nation’s largest, underlying eight states and providing water to tens of millions of people.
Image: U.S. Geological Survey

"[The High Plains] used to be grasslands. The recharge to these systems is going to be minimal," said Virginia McGuire, another USGS research hydrologist. "You pump that water out, and with recharge at about an inch a year, it'd be a heck of a long time before you get it back."

Drought exacerbates the problem in a number of ways. First, the slight recharge that would occur in wetter years is all but absent during times of dryness. And then, of course, farmers have to lean more heavily on groundwater in the absence of precipitation.

"If there's a big reservoir of good quality water that's sitting hidden beneath our feet, people who rely on water are going to pump their wells as they need it," Konikow said.

Pumping without meters
Agriculture claims 96 percent of the water taken from the country's aquifers, but managing that use can be tricky, McGuire said.

Among the High Plains states, only Kansas mandates that its farmers meter their water use, she said. For the rest, water managers have to assemble a massive amount of indirect data -- from the power usage of water pumps to test wells to meteorological data -- to try to estimate how much water is being used in a given year.

"You see different approaches to monitoring and controlling water use as you look across the High Plains," she said. "In Kansas, you have water metering; in Oklahoma, it's referred to 'mining for water,' and the state has the ability to regulate the amount of water pumped."

Texas, however, stands out for its relative lack of regulation. "The rule of capture has existed here since the 1940s," said the Texas Water Development Board's Hopkins. "Essentially, the biggest straw wins."

The recent declines have shocked many districts to reconsider their options, she said. And as they do so, they're realizing that a managed decline might be their only feasible course forward.

"They've gone ahead with 'We're going to deplete our resource.' That's an assumption in the regional water plans," she said. "What they're trying to do now is manage that depletion in such a way that they can adapt to it."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500