Arizona's Willcox basin is sinking fast due to groundwater extraction

In Arizona's Willcox Basin, just over an hour east of Tucson, fissures are tearing through the earth, wells are running dry, and strange areas are flooding when it rains. The cause is clear. As large agricultural producers pump more and more groundwater for irrigation, the water table is falling, and the land surface itself is sinking.

"For a long time," says Dr. Danielle Smilovsky, a geospatial research scientist at the Conrad Blucher Institute, "there were no water regulations there."

In new research presented at GSA Connects 2025 in San Antonio, Texas, U.S., Smilovsky cataloged the extent of subsidence in the area from a five-year study spanning 2017–2021. Using data from satellites that survey changes in the ground surface, she found some areas were sinking at rates of up to six inches per year, and almost three feet over the study period.

Since the 1950s, the ground surface has sunk as much as 12 feet in the area. Currently, the Willcox Basin is experiencing the fastest subsidence in the state, but subsidence is a problem all over Arizona.

The subsidence occurs when groundwater pumping exceeds the recharge rate. As groundwater levels fall, the pore space between sediment grains in the subsurface is no longer filled with water, which usually acts like a hydraulic lift to prop up the sediment and resist the pressure of all the material stacked above.

"Over time, those pore spaces that were once being held open by water pressure start to collapse," says Brian Conway, a geophysicist at the Arizona Department of Water Resources, "and that causes the overlying surface to sink because of the compaction that's happening in the subsurface."

According to Conway, not only does this subsidence cause noticeable impacts on the surface like those fissures, it also creates a more pernicious problem. Once the sediment compacts, the change is permanent. Even if the groundwater is recharged, that storage space is lost forever. In a desert setting, every bit of water storage helps and a permanent loss of aquifer space makes sustainable water use even more difficult.

In the winter of 2022–2023, above-average precipitation and a buildup of a significant snowpack in the mountains gave officials and local residents hope that groundwater recharge might help stop the subsidence. Smilovsky found, however, that the hot, dry summer that followed mitigated any long-term benefits. While the subsidence rates did temporarily slow in the Willcox Basin, it was insufficient to stop the sinking.

Even so, there is hope that subsidence in the area could soon improve. One tool policymakers have to manage groundwater levels and prevent further subsidence is to declare a region an Active Management Area, or AMA. This year, they did just that after a ballot initiative in 2022 to do so failed. While the details of the regulation are still being worked out, AMAs have helped significantly in other Arizona basins experiencing subsidence.

"Especially in the Phoenix and Tucson areas, groundwater levels are recovering, and we've seen subsidence rates decrease quite a bit," says Conway. "In the Tucson area, we're not even seeing subsidence anymore with the groundwater management."

But, the changes that have happened already in the Willcox Basin are locked in. "It needs to not be a desert" with such high demand for groundwater to significantly recover water levels, says Smilovsky. "I don't think subsidence will ever stop, but an AMA might slow it down a bit."