Extreme groundwater depletion in parts of Texas and Kansas may make growing irrigated crops like corn unsustainable in these states within the next 30 years, according to a study by researchers at the University of Texas.

The study fused data from water well readings, NASA satellites, and computer models to create maps that show increased ground water depletion in California’s Central Valley and the High Plains, an agricultural band around the middle of the U.S. that stretches from the Panhandle to South Dakota. The time range shown in the maps and graphs spans from the early and mid-1900s to present day.

Together, the valley and the plains account for a large part of the country’s food production, making the depletion trends uncovered by the study a matter of national food production concern. In 2007 alone, the valley and plains accounted for $56 billion of food supplies.

“I think it’s very important to understand where and when depletion occurs in order to better manage the system,” said Bridget Scanlon, the leader of the study and a senior research scientist at UT’s Bureau of Economic Geography.

The study estimates that eight percent of High Plain and 14 percent of Central Valley pre-irrigation groundwater reserves have been depleted.

One of the most striking findings uncovered by the study is that 35 percent of the groundwater depletion in the High Plains was in only 4 percent of the land area, with most of the depletion being focused in Kansas and Texas.

The reason for such a small amount of land depleting such a large percentage of groundwater is the rate of recharge, or how long it takes for surface water to seep deep into the ground and replenish the groundwater. The northern regions have a recharge rate that can sustain irrigation agriculture at current pumping rates, but the 13,000 year recharge rate for the south makes groundwater a limited resource that can be essentially pumped dry.

“The rate of recharge is so low relative to the rate that is being depleted what it will eventually be exhausted, “said Scanlon.

With the question being not if the groundwater will run out but when, the key area to focus on for irrigation is how to optimize the amount of groundwater that is left in the southern High Plains, said Guy Fipps, the director Texas A&M University’s Irrigation Technology Center.

“What the need is is for improved management of the water,” said Fipps.

Intelligent irrigation systems that precisely determine the water needs of the crop in real time, which are still in development says Fipps, could help fine-tune irrigation practices so groundwater is used only when absolutely needed.
“Irrigation technology just delivers water to the crop,” said Fipps. “Then you have the decisions of how much water to deliver and what’s your timing of irrigation and how frequently do you irrigate. That’s the water management side of the equation.”

There are no stores of excess surface water or water transport systems in the southern High Plains, said Scanlon, so when the groundwater is depleted beyond irrigated agricultural use in these regions farmers will have to switch to non-irrigated crops like the hardy grass sorghum used for animal feed or rangeland.

“Irrigation is critical to our food production,” said Fipps. “As irrigation declines that will have a big impact on the food supply.”

In the Central Valley region the study found that current trends of groundwater use are unsustainable—but not unsalvageable. Unlike the Central Plains, where groundwater has been declining steadily over time, the Central Valley’s groundwater levels are dynamic, plunging during droughts and then recovering.

Although the study still showed a general downward trend in the Central Valley’s levels, Scanlon says that better irrigation techniques and water management can keep the area producing irrigation crops. More efficient drip systems instead of flooding fields and groundwater banking are some of the methods she suggests.

“Groundwater banking is being practiced in California to store excess surface water in aquifers for use for use during drought and this is very successful,” said Scanlon.

The study was published in the May issue of the journal “Proceeding of the National Academy of Sciences.”