Irrigated Crops on the US High Plains

Drought, aquifer use, and the future of agriculture

Susan Walter

December 15, 2023

Fields, many irrigated, near Dimmitt, TX on September 5, 2022.

Hidden Water

Approximately one-fifth of the total U.S. crop and animal agricultural output is grown in a semi-arid climate in the middle of the country. Early European American settlers viewed these smooth prairies as prime agricultural land without knowing the cycles of drought this region experiences, making early attempts at wide-spread cultivation fraught with cycles of failure. As soon as technology allowed, the settlers of the area drilled deep wells, and found a seemingly unlimited supply of groundwater. Irrigation with groundwater significantly changed the agricultural experience by reducing drought risk and allowing for higher-profit but more thirsty crops to be grown, and with higher yields.

The US High Plains are the higher elevation portion of the North American Great Plains between the Rocky Mountains on the west and the Central Lowlands on the east that receive an average of only 10 - 20 inches of rainfall each year. The High Plains Aquifer, also known as the Ogallala, lies beneath the High Plains, from the southern edge of North Dakota, through eight states and into Texas. The Ogallala Aquifer was formed millions of years ago from streams flowing eastward, carrying the eroded sediment from the growing Rocky Mountains and from windblown sediment. Now underground, it is composed of poorly sorted layers of clay, silt, sand, and gravel that holds about the same volume of water as Lake Huron, water that has been there for so long it is called fossil water . Modern irrigation has turned the land above it into the highly productive cropland of today, with yields on irrigated fields often two to four times greater than those on dryland fields. Almost 95 percent of water pumped from the Ogallala is used for irrigation . But in the Central and Southern portions of the aquifer, the water is being pumped much faster than it can be replaced through recharge. It is essentially a non-renewable resource. By looking at what crops are being grown with and without irrigation in the region, this analysis aims to give a broader perspective on what is driving the water use, and what it might mean for the future of crops in this region.

A Brief History of Crops on the High Plains

Agriculture on the North American Great Plains has been a risky business even from its beginnings around A.D. 850 in semi-sedentary horticultural villages along the Missouri River and its tributaries. Native American farmers (who were mostly women) grew plots of maize, beans, squash, amaranth, chenopods, sunflowers and some tobacco on fertile floodplains near their settlements, but had always been plagued by drought, grasshoppers and early frosts. These farmers developed sophisticated risk-management strategies by growing different varieties of each plant, widely distributing their plots, and intercropping, such as growing beans among corn plants.

European American migrants moved into the Great Plains after 1854, bringing “American” farming practices from the East and Midwest with a new crop: wheat. Homesteading farmers had to “break” the prairie with a large plow blade capable of turning over the thick sod. In the 1870s and 1880s, farmers in Kansas chose between planting corn or winter wheat as their primary crop, trying to predict which would be the most profitable crop for that year. Drought in the 1890s brought a decline in acres of corn planted, and this trend was not reversed until modern irrigation methods arrived in the area. Drought tolerant crops such as sorghum, which produces grain under the same conditions that causes corn to wither, and barley were introduced as farmers tried to mitigate losses from drought years.

Plowing up the prairie, Oklahoma. — High Plains Settlers c. 1880s and the Dust Bowl in the 1930s

Photo of dugout, Oklahoma c. 1909 — High Plains Settlers c. 1880s and the Dust Bowl in the 1930s

Infamously in the 1930s, the Dust Bowl was brought on by drought, overcultivation, and excessive grazing which had exposed the soil to wind erosion that created massive dust storms. Many Plains areas lost more than 75 percent of their original topsoil, blown as far as Washington D.C., then even further east onto ship decks three hundred miles out into the Atlantic Ocean. The Dust Bowl is considered to be among the top five environmental catastrophes in world history and led to the creation of the Soil Erosion Service (now called the Natural Resources Conservation Service) to fight soil erosion and establish subsidies for land conservation. Dry farming methods were developed to help maximize soil moisture, such as fallow strips of uncultivated land between field strips, or alternating fields and fallow each year, so two years of moisture are available for the next annual crop.

Before the 1950s, the main crops grown in the region were wheat, alfalfa, and sorghum. With the advent of new technologies that brought deep well drilling, electric pumps powerful enough to bring water to the surface, and center pivot irrigation systems allowing widespread industrial irrigation after 1960, corn became a much more viable crop for the region. The potential for increased yields with irrigation combined with the increase of livestock numbers in the area by the 1980s shifted the crops to more corn and soybeans, especially in the north. Irrigated acreage and total corn production greatly increased after the Energy Policy Act of 2005 was passed, which created subsidies for corn ethanol production to help meet the US mandate for renewable energy.

The Cropland in 2022

All cropland vs irrigated cropland in 2022

Using the 2022 Cropland Data from the USDA NASS and Annual Irrigation Maps – High Plains Aquifer (AIM-HPA) produced from Landsat satellite data, this analysis compares all crops to those located in fields where irrigation is present. By comparing the data of these two maps, the percentage of crops and specific crops grown with irrigation were calculated.

Ninety-five percent of High Plains fields were planted with seven crops in 2022: corn, winter wheat, cotton, sorghum, soybeans, alfalfa, and millet.

This analysis calculates that nearly forty-four percent of fields were irrigated. Of the total cropland, a full twenty percent was irrigated corn fields, eight percent soybeans, and about 4.5 percent each of cotton and winter wheat.

Of the corn crop, 61 percent of the fields were irrigated. Nearly 70 percent of soybean fields were irrigated. Cotton was irrigated in about one-third of cotton fields, and winter wheat in about 22 percent of wheat fields.

Demand for corn has been driven by two factors: increase in livestock in the region, and the US mandate for renewable energy. Animal feedlots had become well established in the region by the 1980s due to the plentiful groundwater resources, isolation from large urban areas, and nearby feed grain production. Today, approximately 35 percent of the US corn supply is consumed by livestock. The Energy Policy Act of 2005 that created subsidies for corn ethanol amplified the demand for corn and after which the number of irrigated acres greatly increased. By 2010, 42 percent of the US corn supply was used for ethanol production. (This is one example of environmental policy having consequences to the environment in other unintended ways.) In 2023, US airlines heavily invested in corn ethanol production to help meet their sustainable fuel goals, which would likely require almost doubling US ethanol production.

Soybeans are grown in about 12 percent of this region’s cropland and nearly 70 percent of the soybean fields are irrigated. This makes irrigated soybean fields eight percent of the total cropland. The crops grown in eastern Nebraska are almost exclusively corn and soybeans intermixed, as soybeans are used as a rotational crop with corn. Soybean plants fix nitrogen in the soil by storing nitrogen in nodules on their roots, and corn planted after a soybean crop is able to use that nitrogen. But because corn is a heavy feeder crop, it depletes nitrogen from the soil, so soybeans are planted again. Studies have shown a yield benefit for corn grown in rotation with soybeans. Just over 70 percent of the soybeans grown in the US are used for animal feed, 15 percent for human consumption and 5 percent for biodiesel.

The climate in Texas is suitable for growing cotton, and much of the irrigated cropland in the southern High Plains was cotton, although only about 32 percent of all cotton fields within the High Plains Aquifer region were irrigated. The harvest in the Texas High Plains was particularly poor in 2022, where farmers reported abandoning 74 percent of their planted crops due to megadrought conditions. Texas grows about 40 percent of the US cotton harvest , and the US contributes about 35 percent of world exports. The majority of cotton grown in the US is upland cotton, which has a short fiber length that is used for a variety of items from apparel, to home goods (curtains, upholstery) to medical and hygiene applications (gauze pads, tampons, cloth diapers). Cotton seed is crushed to separate the oil (used as cooking oil, shortening and salad dressing) from the meal and hull (used as livestock and fish feed). The growth of cotton supply and demand are being driven by world population and economic growth, but when cotton prices rise too high, manufacturers can substitute synthetics, which dampens demand for cotton.

Aquifer Decline

Once thought to be an unlimited supply of water, well monitoring of the Ogallala Aquifer has shown substantial declines in groundwater levels in the Central and Southern regions, and by 2010, roughly 30% of the water had been depleted. One analysis of water decline trends that used water table elevation data from 1935 to 2012, estimated “the lifespan of some of the most productive portions of the aquifer can be measured on the order of decades, with substantial depletion of currently irrigated areas of the Southern High Plains and Central High Plains by 2100." There are still significant acres of cropland being irrigated in these regions. All of the High Plains regions have a precipitation deficit for the last 5 years, but the central region is 9 to 14 inches below normal, and the worst deficit is in the southern region which has had 15 to 18 inches less than normal. This precipitation deficit is one explanation for the persistence of irrigation even in areas with severe water table declines.

Groundwater use in Kansas is monitored by groundwater management districts, and landowners who irrigate more than two acres must apply for water use permits. However, a recent audit showed little accountability for the state’s falling groundwater levels and brought renewed focus on the near-crisis state of water in western Kansas. Recently-passed laws aim to increase the accountability of the groundwater management districts and provide more funding for conservation efforts.

Texas law states that "a landowner owns the groundwater below the surface of the landowner’s land as real property," although the courts have ruled that groundwater is subject to reasonable regulation through the rule of capture. Local Groundwater Conservation Districts (GCDs) are the main regulator of groundwater in Texas, but challenges to GCD authority are increasing state-wide.

In the counties with water table declines of ten meters or more, corn, cotton, winter wheat, and sorghum were the most irrigated crops in 2022.

The sustainability of current levels of irrigation in the central and southern regions of the High Plains Aquifer is already being tested in some areas, and wells have already gone dry. Some farmers in western Kansas switched to dryland farming , from irrigated corn to non-irrigated wheat and grain sorghum due to declining groundwater levels. The profits are not as high, but they make enough to keep their farm in business and to support their family. Going into the 2022 growing season, some farmers in Texas concentrated their crops to only their most productive acres or only planting half their fields because of the continuing mega-drought conditions and groundwater declines.

The National Oceanic and Atmospheric Administration (NOAA) estimated total crop and rangeland losses from major weather and climate disasters in 2022 at over $21.4 billion, with drought and wildfires alone accounting for over $20.4 billion in losses. Texas farmers experienced the highest total crop losses of all states, including $2.9 billion to their cotton crop and $1 billion in wheat damage, mainly attributed to widespread exceptional drought conditions.

When the groundwater runs dry, the cropland productivity of the Central and Southern High Plains will be reduced to dryland yields and again be highly susceptible to drought cycles. Twenty-four percent of the current cropland may be unsuitable for dryland crops and would need to convert back to grasslands (potentially pasture or rangeland). The Northern High Plains (mainly Nebraska), where most of the water storage in the Ogallala is and where there is little net decline will be less affected at current trends.

The restoration of High Plains wetlands, called playas , could also play a role in the future of the central and southern High Plains Aquifer and to any future agriculture in the region. These clay-lined basins that form at the lowest point in an enclosed watershed experience wet-dry cycles essential to their functioning. When it rains, water fills the playas and slowly seeps through the cracks in the clay bottom and filters through to the aquifer beneath. The cracks are slowly filled in and the remaining water is held in the playa lake until it is evaporated, and it remains dry until the wet cycle begins again. Agriculture and urbanization have led to widespread losses and deterioration of these wetlands that have been filled, leveled and bisected with roads or poorly managed grazing. Conserving and reestablishing the wetlands could help increase aquifer recharge.

Is Agriculture at an Inflection Point?

Agriculture has made huge strides in productivity and increased output in modern times, allowing US food prices to be relatively stable. The trend from the past 20 years in agriculture has been industrialization and maximizing "economies of size" in order to maximize production and profits, and many small farmers have not been able to compete. This increase in productivity is not going to be possible forever, and at some point is likely to be in much slower increments. If the "easy" improvements have already been made, it could be more expensive and take more resources to continue to find gains. Food prices will depend on supply and demand forces but also unexpected disruptions, such as what happened to US egg producers when increased feed costs came at the same time as an outbreak of avian flu that killed roughly one in 10 chickens, causing a spike in egg prices in 2022.

Substantial improvements in crop genetics have allowed for increased yields and more drought tolerant plants. For example, dryland corn yields today are comparable with irrigated yields from 40 years ago. By 2016, 91 percent of all corn acres in the US were planted with some form of genetically engineered seed. It is possible newer technologies can help with selection and seed development, but new plant varieties still need multiple, full growing seasons in real-world conditions to be tested. With the gains of the last 40 years, we will have to see if improvement in drought tolerance through genetics and increase in yields can continue at the same rate.

Irrigation efficiency is an area where improvements could be made quickly. A simple first step is to make sure existing equipment is in good repair and not wasting water. The next step could be adding soil moisture sensors and irrigation timers to ensure the fields are not receiving more water than needed. New technologies such as drip irrigation or subsurface irrigation could also help, but many new systems are expensive to install. Of course, the efficiencies gained in irrigation can also encourage the total amount of land irrigated to increase, which cancels out the efficiency gains.

Demand could change. If the US is successful in switching from combustion engines to electric motors, it could reduce the demand for corn converted to ethanol for biofuel, unless that demand switches to aviation fuel . (Biofuels are not always more environmentally friendly than fossil fuels, depending on a variety of factors.) The industry or policy makers could choose to subsidize different crops for ethanol production. The demand for corn for livestock feed does not seem likely to be less in the near future as developing countries are driving an increased appetite for meat products worldwide; however, livestock could be fed with other grains such as sorghum.

Farming has never been easy. So much is out of a farmer's control and difficult to predict: weather; market prices; seed, fuel and fertilizer prices; pathogens or pests that can suddenly appear . Throughout human history, Earth has experienced natural changes to its climate, and the civilizations that survived were the ones able to adapt to the changes in sustainable ways. Agriculture continued on the High Plains even after the Dust Bowl, because farming practices changed and because the government put focus on land conservation. Modern advances in agriculture have been focused on maximizing yields and profits, but with climate change (this time human-induced) causing disruptions and requiring adaptations, the goals need to be adjusted. When a region is relying on a finite resource such as using groundwater for irrigation from an aquifer that does not quickly recharge, the existing practices, policies, and regulations will at some point need to change to focus on sustainability and resource conservation over maximum productivity.

Methodology

The maps and data processing for this analysis was done using ArcGIS Pro. Rasters are 30 meter resolution. The projection of all maps and data is the North American Albers Equal Area Conic HPA (High Plains Aquifer), with the central meridian at -101° longitude. The cropland raster data (USDA 2022) was reclassified using the irrigation raster (Deines et al. 2019) as the input to returned only the cropland that overlapped with irrigation. The Summarize Categorical Raster tool was used to count the crops within each county on both the total cropland raster and the irrigated cropland raster to create the county irrigation maps and crop percentage charts. The water table decline was calculated using 1935 and 2016 level estimates by county (Haacker et al. 2023).

The irrigation data used (AIM-HPA) is from 2017, the most recent year available. The AIM-HPA study used a variety of spectral characteristics and indices, mainly greenness, wetness, and thermal properties, to distinguish irrigated fields from rainfed fields in an effort to capture all irrigation and not only center-pivot; the estimated accuracy is 91%. The accuracy of this analysis would be better with irrigation data from the same year as the cropland data, especially if irrigation was added to active fields between 2017 and 2022. If a field that had been irrigated in 2017 was not active in 2022, that should not affect these results since the irrigated crop raster was created by returning only crops located in pixels that overlapped with the AIM-HPA raster, but error is possible if a field identified as irrigated in 2017 was planted but not irrigated in 2022. The Cropland Data Layer has an estimated overall accuracy of 81%.