120-4 Recharged but Not Recovered: InSAR Observations of Persistent Land Subsidence in Arizona’s Willcox Basin

Session: Land Surface Subsidence: Processes, Impacts, and Ongoing Challenges

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Land subsidence in the Willcox Groundwater Basin of southeastern Arizona represents one of the most severe examples of aquifer system compaction in the western United States. Driven primarily by decades of intensive agricultural groundwater extraction, the region has experienced cumulative vertical land surface displacements exceeding 11 feet in some locations since the mid-20th century. This long-standing geomechanical response to aquifer overdraft has resulted in widespread earth fissuring, damaged infrastructure, and continued groundwater table decline.

Advancements in satellite based remote sensing, particularly Interferometric Synthetic Aperture Radar (InSAR), have revolutionized the monitoring of land surface deformation. Multi-temporal InSAR time series derived from missions such as ESA's Sentinel-1 and JAXA's ALOS have enabled the precise quantification of subsidence rates over the Willcox Basin, revealing two major deformation zones with rates exceeding 15 cm/year. When validated with ground-based GPS benchmarks and groundwater level records, these InSAR datasets provide a powerful, non-invasive means of tracking aquifer health and land surface dynamics.

In recent years, southeastern Arizona has experienced above-average precipitation, leading to temporary and localized recharge within the basin. While some areas have shown minor improvements in groundwater levels, particularly in the fine-grained sediments of the Willcox Playa, InSAR and GNSS observations confirm that land subsidence remains persistent and, in some zones, is still accelerating. The natural recharge is insufficient to offset long-term groundwater deficits that exceed 100,000 acre-feet per year in this region.

The recent launch of the NASA-ISRO Synthetic Aperture Radar (NISAR) satellite represents a transformative advancement in global subsidence monitoring. NISAR’s dual-frequency L- and S-band SAR system will enable higher temporal resolution and deeper penetration through vegetation and dry soils, improving the detection of subtle and seasonal land surface movements. With its unprecedented coverage and revisit time, NISAR will greatly enhance our ability to detect and monitor aquifer-system deformation in vulnerable basins like Willcox.

InSAR technology has fundamentally reshaped our understanding of subsurface hydrological processes. It provides actionable insights to resource managers and policy makers seeking to balance water sustainability with agricultural productivity. The Willcox Basin continues to serve as both a cautionary example and a proving ground for the future of satellite-based groundwater monitoring.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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