A group of farmers in northwest Texas began 2012 under circumstances their forbearers could scarcely imagine: they faced a limit on the amount of groundwater they could pump from their own wells on their own property.
In Texas, a bastion of the free-market Tea Party, such a rule is hard to fathom. Most of the state abides by the “rule of capture,” which basically allows farmers to pump as much water as they want from beneath their own land. But irrigators in northwest Texas rely on the Ogallala aquifer, an underground water reserve that is all-too-rapidly disappearing. If the region is to have any future at all, water users must find a way to curb the pumping.
The Ogallala is one of the nation’s largest and most productive underground water sources. It makes up more than three-quarters of the High Plains aquifer, which spans 175,000 square miles and underlies parts of eight U.S. states — Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. Water drawn from it irrigates 15.4 million acres of cropland, 27 percent of the nation’s total irrigated area.
Initially farmers settling in the High Plains relied on windmills to help them lift groundwater from beneath the surface. But in the 1940s and 1950s, with the introduction of powerful pumps, large sprinkler systems and abundant supplies of natural gas and electricity, irrigation in the High Plains took off. Since 1949, the area under irrigation has risen more than five-fold. Groundwater withdrawals rose in tandem, resulting in a large-scale and ongoing depletion of this critical water reserve.
According to a new study just released by the U.S. Geological Survey (USGS)
, since 1940, the total volume of water in storage in the High Plains aquifer declined by some 266 million acre-feet – a volume equivalent to two-thirds of the water in Lake Erie. (An acre-foot is the volume of water needed to fill an acre of land a foot high. One acre-foot equals 325,850 gallons.)
Even more worrisome, the draining of the High Plains water account has picked up speed. The average annual depletion rate between 2000 and 2007 was more than twice that during the previous fifty years. The depletion is most severe in the southern portion of the aquifer, especially in Texas, where the water table beneath sizeable areas has dropped 100-150 feet; in smaller pockets, it has dropped more than 150 feet.
Unfortunately, that water is not coming back any time soon. The Ogallala filled slowly during the Ice Age tens of thousands of years ago. The southern portions get very little recharge today.
“[I]n less than 100 years we are seriously depleting what took Nature more than 10,000 years to fill,” said USGS director Marcia McNutt.
The Texas irrigation district’s new pumping rule is just one step in the process of adapting to the very real threat of running out of water. The rule is designed to help meet the District’s forward-looking “50/50 Management Goal”: to ensure that in 50 years at least 50 percent of its Ogallala groundwater remains.
It won’t be an easy goal to meet. The new USGS study found that 29 percent of the Texas’ portion of the Ogallala has already been depleted.
But the Texas irrigators have already begun adapting. They have shifted from old-style flood irrigation to more efficient sprinklers. The High Plains Water District maintains that irrigation efficiency rose from 50 percent in the mid-seventies to 75 percent by 1990. Since then, more farmers have adopted low-pressure drop-line sprinklers that deliver water closer to the crops instead of spraying it high in the air. When combined with field methods that conserve water in the soil, these precision sprinklers can achieve efficiencies of 95 percent. Some cotton farmers that have installed sub-surface drip systems, which deliver water at low volumes directly to the crops’ roots, have achieved efficiencies approaching 100 percent.
All of this, and more, will be needed to sustain agriculture in the face of the dwindling Ogallala – especially as energy costs rise and water tables fall.
The recent drought in Texas is a reminder, too, that hotter, drier times likely lie ahead for the Lone Star state. The less crops get watered naturally by rain, the more they need irrigation to make it to harvest.
For irrigators in the High Plains Water District, the pumping cap for 2012 and 2013 is set at 1.75 acre-feet per acre per year. It drops to 1.5 acre-feet for 2014 and 2015, and then to 1.25 acre-feet per acre for 2016 and subsequent years.
As the pumping limits get more stringent, irrigators will need to choose crops and irrigation methods that maximize water productivity – that is, value per drop. And as farmers have more incentive to boost their water productivity, engineers, agronomists and entrepreneurs will develop irrigation systems that help them do this.
It is the way of our water-limited future. Let the adaptation begin.
Image credit: Aerial view of center-pivot irrigation in the High Plains, with its distinctive circular shape. Photo by John Charlton, Kansas Geological Survey.