Quantifying Vertical Deformation in the Tigris–Euphrates Basin Due to the Groundwater Abstraction: Insights from GRACE and Sentinel-1 Satellites

Abstract

This study explores the occurrences of land subsidence in response to dropping groundwater levels in the central part of the Tigris-Euphrates basin. We estimated the groundwater depletion related to human and climate drivers between 2003 and 2017 based on estimates from the Gravity Recovery and Climate Experiment (GRACE) and two global hydrological models (NOAH-3.3 and WGHM-2.2d). The cumulative displacement was calculated using Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) for 96 interferograms, which were generated by 31 images acquired by the Sentinel-1 satellite. The results show that the basin is experiencing a decline in groundwater storage at a rate of −7.56 km 3 /year with a total loss of 106.81 km 3 . This depletion rate has led to inelastic compaction and has resulted in subsidence near the city of Baghdad at a rate of −10 mm/year. The measured coherence phase between the two signals is~0.67, and the depletion precedes the subsidence by~1.5 months. The new data from GRACE-Follow on, Sentinel-1, and the piezometric water level could help to constrain the rate of depletion and displacements in the basin. Combining these remote sensing techniques provides an independent tool for water management in areas where in-situ data are scarce. the subsidence rate is estimated to be >5 cm/year and has increased to 30 cm/year in local regions based on the interferometric synthetic aperture radar (InSAR) technique [11]. This research investigates whether the aquifers in the TEB are suffering inelastic compaction due to the massive groundwater extraction, the decline of water levels, and the progressive drought in recent years.We address this question by first providing evidence for the groundwater depletion and land subsidence in the TEB. Then, we prove that such subsidence is related to the rapid extraction of the groundwater in recent years. The impetus for this investigation is the scarcity of real in-situ data, including piezometric water levels and sufficient subsidence monitoring systems (e.g., levelling systems and the Global Positioning System (GPS)). To overcome this issue, we combine information from the geodetic satellites (Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1) with Global Hydrological Models (GHMs) to better understand the changes in groundwater storage (GWS) and explore the climate and human-driven depletion in the basin.GRACE is sensitive to the total mass variation based on temporal changes of the gravity field [12]. Thus, it can provide the changes and trends of GWS with the help of GHMs. Sentinel-1 satellites offer a tool to estimate the crustal deformations at the millimeter scale, which can be seen as a change of the hydraulic head in aquifer regions. We used the Small Baseline Subset Interferometric Synthetic Aperture Radar (SBAS-InSAR) [13] for data from the Sentinel-1 satellite between 2015 and 2018 to resolve the temporal and spatial subsidies in the central part of TEB. To determine the relationship between the depletion and land subsidenc...

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