Extensive groundwater pumping in southeastern Arizona’s Willcox Basin is causing the ground to sink at an alarming rate, according to a new study. The research, which utilized satellite-based radar data, reveals that some areas of the basin have subsided by as much as 12 inches in the last decade, posing significant risks to infrastructure and the long-term viability of the region’s agricultural economy.
The primary driver of this land subsidence is the overdraft of the underground aquifer, where water is being extracted far more rapidly than it can be naturally replenished. As water is removed from the fine-grained sediments of the aquifer, the clay and silt particles compact, leading to a permanent reduction in the total storage capacity of the aquifer and causing the land surface above to collapse. This phenomenon not only damages buildings, roads, and irrigation canals but also exacerbates flooding risks in low-lying areas.
Satellite Data Reveals Widespread Sinking
Researchers used Interferometric Synthetic Aperture Radar (InSAR) to map the land subsidence across the Willcox Basin with unprecedented detail. By comparing radar scans taken over several years, scientists can detect subtle changes in ground elevation. The data revealed that the subsidence is not uniform, with the most severe sinking occurring in areas with high concentrations of agricultural pumping. The InSAR observations were correlated with groundwater level data from monitoring wells, confirming that the areas with the largest water level declines corresponded to the zones of most rapid subsidence.
Impact on Agriculture and Infrastructure
The Willcox Basin is a major agricultural hub for Arizona, known for its production of corn, alfalfa, and pecans. However, the very industry that sustains the local economy is also contributing to its potential demise. The sinking land has already caused millions of dollars in damage to critical infrastructure. Fissures and cracks have appeared in roads and building foundations, and the structural integrity of irrigation canals and pipelines is under threat. In some cases, farmers have had to deepen their wells to chase the declining water table, a costly endeavor that only exacerbates the problem.
Regulatory Challenges and Water Management
The Willcox Basin is one of several agricultural regions in Arizona that has been designated as an Irrigation Non-Expansion Area, which limits the development of new irrigated acreage. However, there are currently no restrictions on the amount of groundwater that can be pumped from existing wells. This lack of regulation has led to a “race to the bottom” scenario, where individual users have an incentive to maximize their water extraction before their neighbors do, leading to the rapid depletion of the shared resource.
Calls for an Active Management Area
In response to the growing crisis, there have been increasing calls from local stakeholders and water resource experts to designate the Willcox Basin as an Active Management Area (AMA). An AMA designation would grant the Arizona Department of Water Resources the authority to implement mandatory conservation programs, measure and report water use, and establish a long-term management plan to bring the basin into a sustainable balance. However, such proposals have faced resistance from some agricultural interests who are concerned about the potential economic impacts of pumping restrictions.
Future Projections and Long-Term Outlook
Without significant changes in water management practices, the land subsidence in the Willcox Basin is projected to continue, and may even accelerate. The permanent loss of aquifer storage capacity is a particularly concerning aspect of the problem, as it means that even if water levels were to recover in the future, the basin would not be able to hold as much water as it once did. This has long-term implications for the region’s water security, especially in the face of a changing climate that is expected to bring more frequent and severe droughts to the southwestern United States.