Where's all the water?

By Joli A. Hohenstein

How can we be in the midst of a changing climate that can generate more intense rain, yet face a potential lack of water availability as that same climate change progresses?

It all depends on where the water is in relation to agricultural production. It’s true that changes in precipitation may lead to a decrease in demand for irrigation because non-irrigated production may be more profitable, says Noel Gollehon, Water Policy Economics, Gaithersburg, Maryland.

But, it’s also true that for every 100 drops of rain that fall on land, only 36 drops actually come off as “blue water,” or rainfall that replenishes streams, lakes and aquifers. The other 64 drops stay on the landscape as “green water.” As soils dry out from climate change, Gollehon says they absorb more rainfall when it happens, and that leaves less “blue water” available for use.

Changing Climate Challenges

Changing precipitation patterns add to those challenges, with less frequent but more intense weather events — harder, powerful rains and hotter droughts, for example.

“The rainfall amounts will come more in heavier events, and that can cause soil erosion,” says David Emory Stooksbury, professor of engineering and atmospheric sciences at the University of Georgia, Athens. “These glacial-till soils have the ability to recharge quite quickly, but if the rain is coming down too fast, most of that is going to run off.”

In some areas, production adjustments such as cultivar selection could accommodate changes. “That could mean you have to irrigate at critical times,” Stooksbury says. “It might also mean switching to different crops, though part of that could be taken care of by cultivar selection.”

In other regions, it isn’t so easy.

“What you face in the Midwest is not the same problem we have on the Ogallala Aquifer, where we’re mining a non-renewable resource,” says Reagan Waskom, director of the Colorado Water Institute in Ft. Collins. Simply put, supply can’t keep up with demand.

As one of the world’s largest aquifers, the Ogallala lies beneath the sand, gravel, clay and silt of the Great Plains under eight states: Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas and Wyoming. That means it supports nearly one-fifth of U.S. wheat, corn, cotton and cattle production. As more farmers irrigate and pump more water from the Ogallala, the aquifer’s level drops at an alarming rate — as much as two feet per year.

“The future of the Great Plains bread basket is interesting,” Waskom says. “Higher temperatures lead to higher crop evapotranspiration needs. That means less recharge to the aquifer.”

What’s more, Waskom says, “Our roughage (silage and alfalfa) for feedlots and dairies tends to be more locally sourced — we’re already shipping in corn and soybeans. If we can’t produce roughage and have to start shipping it in, what does that look like? Cotton is creeping into Colorado and Kansas. We’re seeing more corn in the Dakotas. The local economy may change.”

Noel Gollehon

Irrigation Options

Illinois irrigation traditionally occurs in areas with sandy soils such as along river valleys. Close to one-third of the pivots are in Mason County. Most areas are fortunate to have enough rainfall to recharge aquifers, but those with sandy soils face different challenges with climate change.

“If you have 30 to 50 feet of drawdown on an aquifer buried under 50 feet of clay in Champaign County where there are 70 irrigation systems, that’s different than other parts of Illinois with 2,300 irrigation systems relying on an aquifer system just under the surface of sand,” says Steve Wilson, groundwater hydrologist with the Illinois State Water Survey, Champaign.

Changing climates are already driving adjustments in how Illinois farmers manage water. “What we’ve seen in the last 10 years is more irrigation on better soil,” he says. “If you have contracts for seed corn or beans, you need to have a guaranteed crop. If we have more dry years, you’re going to see more irrigation systems where they can be sustained.”

In some parts of Illinois, there is no groundwater available. Recent ethanol plant construction is a great example of what can happen, Wilson notes. “Some were built where there was no groundwater water, so they bring water in and that’s a very expensive proposition,” he says.

Farmers who are in position where they face an increased likelihood of dry conditions and have irrigation needs that must be augmented have two options, says Gollehon. Retain more soil moisture or green water, or use blue water for irrigation.

However, it’s not as easy as it sounds. “Increasing tilth and soil water holding takes time,” he says. In many areas farmers must have permission from the state to use water for irrigation.

“You don’t have the right to use it just because it’s there. Or you may have the right to water if you border on a stream, but how much water is unknown,” he explains. “You may or may not have groundwater available.”

Forward-Thinking Tactics

With more extremes in weather possible, Gollegon says, “The best thing you can do is be prepared. Understand your property and where you are and what your ground’s capabilities are.

“There’s a reason they irrigate in Arkansas, when you get more rain in Illinois: soil type,” he says. “If you can bulk up soil moisture, that may buffer you out for a period of time.”

While soybean producers may be able to count on rain now, that may not be the case in the future. Historical climate patterns are changing and producers need to be ready.

“You can’t become an irrigation farmer overnight,” Gollehon says. “Learn how it affects your seeding rate, fertilizer and pesticide regime. Know how to run the system. Try it out and get comfortable with the management. It doesn’t happen overnight, and it doesn’t happen easily.”

Producers also must keep an eye on the economics. “Nobody knows when the magic tipping point might be. But if you don’t start now, you will miss the window,” says Gollehon. “It may take 10 years to raise your soil water holding capacity by raising the soil carbon a little at a time. We will look back in 20 years and say that we should have done it 20 years ago.” ■

The Qgallala Aquifer