New model sheds light on groundwater decline by linking irrigation decisions to groundwater use

Sustainable groundwater withdrawal rates in Oregon’s Harney Basin were higher than they were 20 years before groundwater levels were generally acknowledged to be declining, a new analysis finds.

Lagging recognition of the impacts of groundwater use is just one insight gained from new research linking agricultural economics and groundwater hydrology in the Harney Basin. Oregon State University economists and U.S. Geological Survey hydrologists investigated interactions and feedbacks between farm irrigation decisions and groundwater levels to better understand the causes and potential solutions to groundwater decline. developed a model.

“Groundwater is hidden underground, poorly understood, and difficult to manage,” said William Yeager, a professor of applied economics at Oregon State University. “Without effective regulation, water is often extracted at unsustainable rates because individual water users have an incentive to act without considering the impact on others. , which can have negative impacts on all water users and the environment.”

Groundwater levels are declining globally across the United States and in other parts of Oregon, resulting in reduced base flows in rivers and rivers, less water in wetlands, dry wells, and in some cases land subsidence. It is occurring.

“Both the modeling approach and the case study results will benefit managers and researchers outside of Harney County and the state of Oregon,” Yeager said.

The Harney Basin is a sparsely populated, semi-arid region in southeastern Oregon that has experienced increased groundwater pumping since the 1990s, resulting in groundwater table declines over the past two decades. This not only has a negative impact on farmers who rely on groundwater for irrigation, but also on environmental flows such as residential wells and wells that feed the Malheur National Wildlife Refuge. . Recently, it has received attention from state and federal agencies seeking to understand the cause, scope, and possible solutions to the problem.

In the new study, just published in the journal Water Resources Research, analysis found that some solutions that observers thought were promising do little to stabilize groundwater conditions. For example, a scenario that requires the use of more water-efficient irrigation techniques would only pump 5% less water than the status quo scenario, a small improvement.

This scenario shows that only by limiting groundwater pumping by nearly half, the predicted response can stop the decline in groundwater levels, eliminate depletion of non-irrigation wells, and stabilize environmental flows. It shows. A change of this magnitude in groundwater irrigation economics would reduce agricultural profits by $7.5 million to $9 million per year compared to the status quo scenario.

The researchers built a hydroeconomic model based on detailed geological, climate, and well data for groundwater systems, and land use, crop production, and agricultural economics data for agricultural systems. The model also accounts for basin-wide effects on non-irrigated wells and environmental flows.

The researchers used the model to simulate 30-year scenarios under “as-is” conditions, as well as 14 alternative scenarios representing actions aimed at stabilizing groundwater levels.

Under status quo conditions, the model shows a continued decline in groundwater levels, dropping an average of 14 feet over the 30 years of simulation, and up to 65 feet in some areas. In addition, farm profits will decrease by 10%, an additional 65 wells will dry up, and environmental flows will decrease by 19%.

Other scenarios simulate idleness of irrigated farmland, reduce pumping in areas where groundwater levels are expected to decline the most, place limits on the amount of groundwater pumped, and reduce junior water rights. In all scenarios, annual agricultural profits decrease by the 30th year of the simulation. Savings range from $2 million under a status quo trajectory to nearly $14 million under a scenario that reduces maximum pumping rates to a quarter of 2018 levels.

“Model simulations show that significant reductions in water pumping are needed to stabilize groundwater levels, stop the depletion of residential wells, and stabilize environmental flows in the watershed, and that this will reduce the number of people whose pumping has been reduced. “This shows that profits will decline,” Yeager said.

“This situation illustrates a structural problem in groundwater management in Oregon,” Yeager explained. “State water laws limit managers’ ability to respond and adapt to changing conditions, unlike regulations for other resources, such as marine fisheries, which are also uncertain and highly variable. In many coastal fisheries, , the total allowable catch is set by managers, which can increase or decrease from year to year to ensure long-term sustainability, but groundwater managers in Oregon There is no such tool.”

Other authors of the paper are John Antle and Dan Bigelow of Oregon State University and Stephen Gingerich of the U.S. Geological Survey.