Researchers at the University of Montana analyzed decades of data across 221 basins in the Colorado, Columbia, and Missouri river systems. They found that 75% of the water used for irrigating crops is drawn from the rivers and streams flowing throughout the vast study area, which spans 10 Western states.
Agricultural areas using efficient irrigation practices can impact streamflows even more than climate change, said David Ketchum, a hydrologist who led the study. He called these findings an “irrigation efficiency paradox.”
“Very efficient irrigation systems tend to use almost all of the water that they extract from the river and then apply to the field. That doesn’t leave any water to return to the river,” Ketchum said.
This is happening most glaringly in the Snake River basin, which is primarily in Idaho, and San Juan River basin in the Four Corners area, according to the study.
Meanwhile, farming regions using less efficient irrigation leave significant amounts of water unused, said Ketchum, before adding, “and that water is able to drain back into the ground and eventually returns to the river.”
He said this shows that irrigation techniques can be changed to help address the streamflow declines being caused by climate change.
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado, and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.
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