Satellite data shows some areas of Arizona’s Wilcox Basin are sinking more than 6 inches (15 centimeters) per year, making it the fastest sinking area in the state.
This subsidence is the result of intensive groundwater extraction to support agriculture in the region, which lowers the water table in the basin and, with it, the land surface. Previous studies have found that parts of the basin have sunk by up to 12 feet (3.6 meters) since the mid-20th century.
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Groundwater in a basin fills the spaces between dust and soil particles below the earth’s surface. When this groundwater is removed, the space it once filled collapses because the sediment can no longer support its own weight. When the space that once stored water collapses, the change becomes permanent and the basin loses its ability to replenish groundwater.
“Over time, the pores that were once held open by water pressure begin to collapse,” Brian Conway, a geophysicist with the Arizona Department of Water Resources who was not involved in the study, said in a statement. “As a result, the overlying surface sinks due to the compaction that is occurring underground.”
In a new study, Daniel Smilowski, a researcher at the Conrad Blucher Institute at Texas A&M University-Corpus Christi, used a satellite-based technique known as interferometric synthetic aperture radar (InSAR) to measure changes in Wilcox Basin surface height from 2017 to 2021. InSAR measures the distance between a satellite orbiting Earth and a point on the planet’s surface. Scientists can detect small changes in surface elevation over time after averaging multiple measurements taken in succession.
The study revealed that some areas of Arizona sank nearly 3 feet (1 meter) during the study period.
Even heavy rains in 2022 and early 2023 were not enough to stop the subsidence. Higher-than-normal precipitation and snowmelt temporarily raised the groundwater level in the basin, but the land continued to sink. In some areas, speeds have increased even further. This suggests that if groundwater is allowed to recharge naturally, extraction will likely not be able to keep up.
Regulating groundwater pumping could slow subsidence in the future. In 2024, policymakers declared that designating the Wilcox Basin as an Active Management Area (AMA) could limit extraction and preserve the basin’s ability to store groundwater. Details of the management plan have not yet been finalized, but similar plans are helping manage water in other parts of the state.
“Groundwater levels are recovering, particularly in the Phoenix and Tucson areas, and land subsidence rates have decreased significantly,” Conway said in a statement. “In the Tucson area, we have not seen any land subsidence thanks to groundwater management.”
Smilovsky took a more cautious view over the long term. “I don’t think the land will ever stop sinking,” she said in a statement. “But with the AMA, it might slow things down a little bit.”
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