Colorado State University researchers are counting greenhouse gases released from irrigation for the first time, making top-emitting counties more visible alongside ways to help cut emissions.
Agriculture relies on irrigation, the CSU researchers said. It鈥檚 a vital tool for farmers and ranchers to water crops when the rain just isn鈥檛 there 鈥� an increasingly common problem with over two decades of drought and a changing climate in Colorado. But the process of pushing water through pumps, canals and center-pivot sprinklers into soils can add to greenhouse gases in the atmosphere.
Cutting emissions starts with knowing how much is released in the first place, said Avery Driscoll, a doctoral candidate and lead researcher in the peer-reviewed journal Nature Water. It鈥檚 all she鈥檚 been thinking about for three and a half years, she said.
鈥淏efore the study, we really didn鈥檛 know how big of an emissions impact this was,鈥� Driscoll said. 鈥淲e wanted to do this to identify opportunities to irrigate in a way that gives us productivity benefits but also minimizes our emissions impact.鈥�
The buildup of amplifies Earth鈥檚 , which traps heat from the sun and warms the planet, and contributes to climate change.
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Some climate stressors 鈥� longer droughts, more heat waves 鈥� are being felt in Colorado and across the West. Colorado's temperature is rising, and research indicates the state鈥檚 rivers and streams will over the next 30 years as a result.
Reducing the primary greenhouse gas, carbon dioxide often reduces components of Colorado鈥檚 toxic ozone 鈥� a big issue in Colorado鈥檚 nine northern Front Range counties which of EPA limits on toxic ground-level ozone.
Colorado to cut greenhouse gas emissions in half by 2030. To hit the target, the state needs to take big steps like adding rapid transit and plugging more old oil wells, according to .
Driscoll offered more items for Colorado鈥檚 to-do list: switching to electric water pumps and relying on electricity from renewable sources. That way farmers can keep farming, just with less emissions, she said.
鈥淭he goal here is not to say that we shouldn鈥檛 be irrigating,鈥� Driscoll said. 鈥淚t鈥檚 to identify opportunities to use irrigation as an adaptation tool with lower emissions.鈥�
Farmers are already doing a lot of this work, said Greg Peterson, who works with farmers and ranchers across the state as the executive director of the Colorado Ag Water Alliance.
鈥淚鈥檓 sure there鈥檚 more out there using diesel pumps, but I鈥檝e only had one farmer come to me looking for funds to switch from diesel to electric,鈥� he said. 鈥淓very other project I鈥檝e dealt with, we鈥檙e talking about electric pumps.鈥�
Irrigation emissions in Colorado
Driscoll and the team of seven other researchers looked at federal databases, submitted public information requests, interviewed water managers, and more to calculate irrigation emission estimates between 2015 and 2022.
In Colorado, they found that Yuma County was the top-emitting county, releasing about 158,400 metric tons of greenhouse gases.
Most of this came from pumping water on farms. Water pumps 鈥� powered by natural gas, oil, and electricity 鈥� can bring water from deep underground aquifers or push water across sloping croplands.
Water in underground aquifers contains carbon dioxide, which escapes when it is brought to the surface 鈥� like how dumping a can of soda on the ground releases carbonation, Driscoll said.
The other top counties for irrigation-related emissions were Baca County, with nearly 77,560 metric tons; Rio Grande County, with about 74,700 tons; and Saguache County, with less than 72,650 tons.
Groundwater pumping on farms was the main emission source in each county. Another leading source is soil microbes. A particularly potent gas, nitrous oxide, is released by microbes when soils are suddenly moistened by rain or irrigation. Emissions also come from larger pumping systems that move water from one river basin to another, even across mountain ranges.
Most interbasin water systems in Colorado rely on gravity to move irrigation water. But this gets complicated: Denver Water鈥檚 system, for example, was classified as a public supply only 鈥� not for agricultural irrigation 鈥� so it was not included in the CSU research, Driscoll said.
Three systems served irrigators and required energy: the Colorado-Big Thompson Project in north-central Colorado, the Dolores Project in southwestern Colorado, and the Redlands Power Canal near Grand Junction.
These projects deliver water to cities, homes, industries, ecosystems, and croplands across the state, which means turning on a faucet at home also contributes to greenhouse gas emissions.
The Colorado-Big Thompson Project, managed by Northern Water and the Bureau of Reclamation, was the largest. The researchers estimated its irrigation-related emissions to be about 65,470 metric tons and its total emissions to be about 146,280 tons.
It contributes about 6% of the irrigation-related emissions from similar interbasin water systems nationwide. Only two projects in the U.S. contribute more: the California State Water Project, which accounts for 49%, and the Central Arizona Project, which comprises 36%.
One factor that needs to be considered, according to Northern Water, is that the system also uses the flow of water to generate hydroelectric power, adding enough back to the electric grid to more than make up for its energy usage.
鈥淲e still think that we are a net power producer rather than a power user on the system,鈥� said spokesperson Jeff Stahla.
A nationwide look
The CSU study quantifies irrigation-related emissions across the entire United States down to the county level. It鈥檚 the first in the world to do this so comprehensively, Driscoll said.
They found that, nationwide, irrigation produces 18.9 million metric tons of greenhouse gases each year. The entire country of Costa Rica, for example, produced about 15 million tons in 2020, Driscoll said.
That鈥檚 a small slice of the nation鈥檚 total emissions. The U.S. released over 6 billion metric tons in 2022, making it the second-largest emitter globally, according to .
Most of those irrigation-related emissions, about 12.6 million tons, come from small water pumps on farms 鈥� powered by natural gas, oil, and electricity 鈥� that pull up groundwater and move water across sloping fields.
The study also found that irrigation-related emissions concentrate in specific areas, which is encouraging, Driscoll said. It makes it easier to target reduction efforts geographically.
Cutting emissions may be more challenging in some areas than others. Farmers already put solar panels in center pivots and barns but face barriers, like the expense of building a service line to connect a field to the electric grid, Peterson said.
Farmers and ranchers are already taking advantage of new technologies, like special motors called variable frequency drives, that draw on the electric grid more efficiently. They are working with the state, which for agricultural businesses and .
Driscoll hopes the new research helps more of these projects happen.
鈥淥ur hope is that policymakers and producers can use this information to reduce emissions from irrigation in locally relevant ways,鈥� she said. 鈥淧articularly with respect to energy-related emission reductions, we have the tools to make that happen. It鈥檚 low-hanging fruit.鈥�
Shannon Mullane is a reporter for The Colorado Sun. Her work frequently appears on-air at KUNC 91.5 FM and online at KUNC.org. Contact Shannon at shannon@coloradosun.com.