Monitoring ground surface deformation in the Kharga and Dakhla Oases in Egypt using persistent scatterer interferometry technique

Abstract

Agriculture is the primary sector in the Kharga and Dakhla oases of the Western Desert in Egypt. In this region, agriculture relies on the groundwater obtained from the Nubian Sandstone Aquifer System (NSAS). Recently, the groundwater level of this aquifer has been declining, posing a risk to the regional sustainability of the sector. Thus, it is necessary to understand the overall groundwater conditions in this region. Notably, the groundwater information about this aquifer is not publicly available, and its current condition remains unclear. Previous studies have only conducted NSAS assessments on a large spatial scale. Furthermore, no studies have observed land subsidence associated with groundwater use. Observing land subsidence could enable future assessments of the aquifer on a smaller spatial scale. This study is novel in that it observes land subsidence in oases using satellite data. The objective of this study is to promote future investigations of the NSAS by spatially observing land subsidence associated with the decrease in the groundwater level. The regional land subsidence was analyzed using interferometric synthetic radar (InSAR). The vertical surface deformation in the Kharga Oasis varied from −9.35 to 7.48 mm/year, and that in the Dakhla Oasis varied from −10.69 to 7.57 mm/year. The areas of significant subsidence were located within the agricultural land. The well-head uplift phenomena in the irrigation wells were observed in the study area. Thus, the subsidence in the region could be attributed to the large amount of groundwater extraction for irrigation. Significant uplift was also noted in the sand-dune regions and the outer edges of the vegetated area, likely attributed to the sand transport and deposition driven by northerly winds. This study presents a comprehensive analysis of the land subsidence in the Kharga and Dakhla oases and its association with the local decrease in the groundwater level. Consequently, this study successfully demonstrated the potential occurrence of land subsidence caused by groundwater extraction in the oases through the use of satellite-based observations. Notably, our method can be adapted to analyze similar areas worldwide.