Irrigating U.S. crops prevents higher greenhouse gas emissions by avoiding land conversion, groundbreaking new research by Colorado State University shows.
Agricultural irrigation allows the United States to grow more food on less land. If irrigation were suddenly shut off, the land change required to make up for lost yield would produce significantly more greenhouse gas emissions than those emitted by irrigating – 363 times more.
CSU scientists estimate the emissions saved by avoiding land-use change would equate to 363 years' worth of today's U.S. annual greenhouse gas emissions from irrigation.
Converting natural ecosystems to agricultural use releases carbon that's stored in soil and vegetation. Land use and land conversion for agriculture to produce food, fiber and fuel contribute nearly a quarter of global greenhouse gas emissions, making the sector a key priority for emissions reductions, the study published today in Proceedings of the National Academy of Sciences states.
"It was clear from this work that irrigation has a net positive effect on emissions," said lead author Avery Driscoll, who conducted the research as a CSU Ph.D. student. "The avoided emissions from reductions in indirect land-use change were much greater than the direct emissions, and that could decline further with electrification."
Pumping water for irrigation – both on farms and for interbasin transfers – uses energy, which creates the most emissions related to irrigation. This is also the easiest source to solve, the researchers said, by replacing fossil fuel pumps with electric pumps. They suggested policymakers might consider incentives for electrification when developing climate-smart agriculture programs.
In previous studies, the researchers outlined direct emissions from irrigation, which also include smaller amounts of nitrous oxide released through microbial respiration and the dispersal of dissolved carbon dioxide when groundwater is sprayed on fields. Their new research is the first study to compare the costs and benefits of direct and indirect emissions from irrigation.
The avoided emissions due to irrigation amount to 6.86 gigatons – more than the total annual emissions of the U.S. in 2024 (5.91 gigatons), or about 13% of total global emissions that year, Driscoll said.
The researchers said the study demonstrates that climate-smart agricultural policies must consider both direct and indirect emissions impacts.
"This comprehensive approach to accounting for direct emissions from the field and for the indirect land-use impacts lets us identify local opportunities to reduce emissions, through pump electrification and grid decarbonization, while also maximizing benefits associated with increasing productivity," said Driscoll, who is now a postdoctoral researcher at Purdue University. "Ideally, this is a win-win for addressing local emissions and also harnessing the global benefits of irrigation."
To estimate the amount of land and emissions spared, the researchers first mapped yield benefits at the county level across the United States, calculating a ratio of rainfed to irrigated yields using existing survey data and a machine learning model. They then used a global economic model that simulates production, consumption and trade flow to determine how U.S. production would change if it were all rainfed. Based on economic supply and demand, and accounting for the suitability of different crop types in different regions, the global economic model mapped land use change in the absence of U.S. agricultural irrigation.
Using maps of carbon stored in biomass and soils and data on how carbon stocks change under land-use change, they estimated emissions associated with land-use change.
The researchers noted that the study did not look at other agricultural management practices that can lead to emissions, such as nitrogen application on crops or methane from livestock.
"We're able to show this large benefit of U.S. irrigation to greenhouse gas emissions from the food system," said co-author Nathan Mueller, a CSU associate professor in the departments of Ecosystem Science and Sustainability and Soil and Crop Sciences. "Yet, when we talk about water use, particularly in the western U.S., there are trade-offs with every use and trade-offs beyond food and beyond greenhouse gas emissions. Our work provides one piece of the puzzle to help examine some of the very complicated societal cost-benefit questions surrounding water use."
Much of the western U.S. relies on irrigation for food production.
CSU alumnus Alex Brown's family has been farming and ranching the same land in Yuma County, Colorado, for 120 years.
"We need irrigation to fulfill our needs and our duty to continue to feed the world," Brown said, adding that if they couldn't irrigate, farmers would have to plow up less productive and more ecologically sensitive pastureland for crops, and they would be dependent on unreliable rainfall. "As the population increases, the demand for food increases and the demand for agriculture on less land increases."
Brown said producers in Yuma County – one of Colorado's top-producing counties for crops and livestock – take conservation seriously. His family continually works to improve irrigation efficiency through technology and modern equipment.
"I'm very passionate about it because I'd love to see our farm continue on for generations," Brown said about using water wisely.
"Irrigation is a powerful adaptation strategy," study lead Driscoll added. "It increases productivity; it increases resilience to heat and drought stress, and of course, maintaining and increasing agricultural production is a critical priority. At the same time, we need to reduce food system emissions, so understanding how those two challenges interact with one another is a priority. This work allows us to grasp some of those trade-offs and synergies a little better."
The study was funded by the National Science Foundation and by the AI Institute for Land, Economy, Agriculture & Forestry, supported by the U.S. Department of Agriculture. Collaborators included University of Minnesota economist Justin Johnson and researchers Joey Blumberg (U.S. Forest Service Rocky Mountain Research Station), Alison King (University of Maine) and Seth Spawn-Lee (The Nature Conservancy).
