Irrigation’s climate benefit could equal 363 years of its own emissions

Irrigation increases crop yields, which means the same amount of food can be grown on a smaller area. According to the researchers, if irrigation across the United States were suddenly eliminated, making up for the lost agricultural production would require expanding farmland. The greenhouse gas emissions associated with that land conversion would be 363 times greater than the emissions currently produced by irrigation itself.

The team estimates that the emissions avoided by preventing this additional land use are equivalent to 363 years of current annual U.S. greenhouse gas emissions from irrigation.

Why Saving Land Matters for the Climate

Natural ecosystems store enormous amounts of carbon in vegetation and soils. When forests, grasslands, or other landscapes are converted into farmland, some of that stored carbon is released into the atmosphere.

Agricultural land use and land conversion associated with producing food, fiber and fuel account for nearly one quarter of global greenhouse gas emissions, according to the study, published on September 14 in Proceedings of the National Academy of Sciences. That makes changes in agricultural land use an important consideration in efforts to reduce emissions.

“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.”

Where Irrigation Emissions Come From

The largest source of greenhouse gas emissions linked directly to irrigation is the energy required to move water. Pumps are used both on farms and to transfer water between river basins, and when that equipment relies on fossil fuels, it produces emissions.

The researchers say this source could also be relatively straightforward to reduce. Replacing fossil fuel-powered pumping systems with electric equipment could lower irrigation-related emissions, especially as the electricity grid becomes cleaner. They suggest that policymakers could consider incentives for electrification when designing climate-smart agriculture programs.

Earlier studies by the research team examined other direct emissions associated with irrigation. These include smaller releases of nitrous oxide caused by microbial respiration, along with carbon dioxide that is dissolved in groundwater and released when that water is sprayed across fields.

The new analysis is the first from the group to directly compare those emissions with the indirect greenhouse gas benefits created when irrigation reduces the need to convert additional land into agriculture.

Nearly 7 Gigatons of Avoided Emissions

The researchers calculated that irrigation prevents an estimated 6.86 gigatons of greenhouse gas emissions through avoided land conversion.

That total exceeds all U.S. greenhouse gas emissions in 2024 (5.91 gigatons) and is equal to roughly 13% of total global emissions that year, according to Driscoll.

The findings, the researchers argue, show why climate-smart agricultural policies need to account for both the emissions created directly on farms and the indirect effects that agricultural productivity can have on land use elsewhere.

“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.”

Modeling a United States Without Irrigation

To determine how much land irrigation currently spares, the scientists first measured how much irrigation improves crop yields across individual U.S. counties.

They calculated the relationship between rainfed and irrigated crop yields using existing agricultural survey data combined with a machine learning model.

Next, the team used a global economic model that simulates agricultural production, consumption, and international trade. This allowed them to estimate how farming would shift if all U.S. crops suddenly depended entirely on rainfall.

The model considered economic supply and demand as well as which crops could realistically be grown in different regions. From there, researchers mapped where additional agricultural land would likely be needed if U.S. irrigation disappeared.

They then combined those results with maps showing how much carbon is stored in vegetation and soils. Using information about how those carbon stores change when natural landscapes are converted into farmland, they calculated the greenhouse gas emissions that could result.

The researchers noted that their analysis did not include emissions from several other agricultural activities, including nitrogen fertilizer application or methane produced by livestock.

Irrigation Comes With Broader Trade-Offs

“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.”

Those trade-offs are particularly important in the western United States, where much of the agricultural system depends heavily on irrigation.

Water supplies in the region must support farms as well as communities, ecosystems, and other demands, which means the greenhouse gas benefits identified in the study represent only one part of a much broader debate over how water should be used.

A Colorado Farm’s Dependence on Irrigation

CSU alumnus Alex Brown’s family has farmed and raised livestock on the same property 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.”

Yuma County is one of Colorado’s leading counties for both crop and livestock production. Brown said farmers in the region take conservation seriously, and his family continues to improve irrigation efficiency by adopting newer 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 as an Adaptation Strategy

Beyond increasing yields, irrigation can also help farms withstand increasingly difficult growing conditions.

“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 National Science Foundation and the AI Institute for Land, Economy, Agriculture & Forestry funded the study, with support from 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).