New model sheds light on groundwater declines by linking irrigation decisions and groundwater use

Sustainable rates of groundwater withdrawal in Oregon's Harney Basin were surpassed 20 years prior to the time declining groundwater levels were generally recognized, a new analysis found.

That lag in realizing the impact of groundwater use is just one insight from a new study linking farm economics and groundwater hydrology in the Harney Basin. Oregon State University economists and a U.S. Geological Survey hydrologist developed the model of interactions and feedback between farm irrigation decisions and groundwater levels to better understand the causes and potential solutions to the decline in groundwater.

"Groundwater is challenging to manage because it is hidden below ground and poorly understood," said William Jaeger, a professor of applied economics at Oregon State. "It's frequently extracted at unsustainable rates because, without effective regulation, individual water users have an incentive to act without considering impacts on others. This can lead to negative effects on all water users and the environment."

Groundwater levels have been declining globally, across the United States, and in other parts of Oregon, leading to decreases in river and stream base flows, less water in wetlands, wells running dry, and in some cases, land subsidence.

"Both the modeling methods and the case study findings will benefit managers and researchers beyond Harney County and beyond Oregon," Jaeger said.

The Harney Basin is a sparsely populated, semi-arid region in southeast Oregon where groundwater pumpage has increased since the 1990s, resulting in declines in groundwater levels during the past two decades. This has had adverse impacts on farmers who rely on groundwater to irrigate, but also on residential wells and environmental flows, including those serving the Malheur National Wildlife Refuge. It has led to recent attention from state and federal agencies looking to understand the causes, extent and potential solutions to the problem.

In the new study, which was just published in Water Resources Research, the analysis finds that several solutions thought to be promising by observers would do little to stabilize groundwater conditions. For example, in a scenario requiring the use of more water-efficient irrigation technologies, water pumped is only 5% lower than for the status quo scenario, offering only minor improvements.

The scenarios indicate that only by limiting groundwater pumping rates by nearly half do the projected responses halt groundwater-level declines, eliminate drying up of non-irrigation wells, and stabilize environmental flows

The scenarios indicate that only by limiting groundwater pumping rates by nearly half do the projected responses halt groundwater-level declines, eliminate drying up of non-irrigation wells, and stabilize environmental flows. This scale of change in the groundwater-irrigated economy would reduce farm profits relative to the status quo scenario by $7.5 million to $9 million annually.

The researchers built a hydro-economic model based on detailed geologic, climate and well data for the groundwater system, and data on land use, crop production and farm economics for the agricultural system. The model also illuminates basin-wide impacts on non-irrigation wells and on environmental flows.

The researchers used the model to simulate scenarios 30 years into the future under "status quo" conditions and 14 alternative scenarios representing actions aimed at stabilizing groundwater levels.

Under status quo conditions, the model shows continued declines in groundwater levels, dropping by 14 feet on average, with declines up to 65 feet in some areas over the 30-year simulation. In addition, farm profits decline by 10%, 65 additional wells go dry and environmental flows drop by 19%.

Other scenarios simulate idling irrigated farmland, reducing pumping in areas where groundwater levels are forecast to decrease the most, setting limits on how much groundwater can be pumped and curtailing junior water rights. All the scenarios result in lower annual farm profits by year 30 of the simulations. The reductions range from $2 million under the status quo trajectory to nearly $14 million under a scenario that would lower maximum pumping rates to a quarter of the 2018 rates.

"The model simulations indicate that stabilizing groundwater levels, halting the drying up of residential wells, and stabilizing the basin's environmental flows will require substantial reductions in pumping which will reduce profits for those whose pumping is curtailed," Jaeger said.

"The situation illustrates a structural problem for groundwater management in Oregon," Jaeger explains. "The state's water laws limit managers' ability to respond and adapt to changing circumstances, unlike rules for other resources such as ocean fisheries, which are also uncertain and highly variable. For many coastal fisheries, a total allowable catch is set by managers, and this can be adjusted up or down from year to year to ensure long-term sustainability. Groundwater managers in Oregon lack these kinds of tools."