Inferencing the land subsidence in the Nile Delta using Sentinel-1 satellites and GPS between 2015 and 2019.

The Nile Delta is home to half of Egypt's population and has ample agricultural, industrial, and cultural resources, yet the land subsides in response to many natural and anthropogenic impacts. We report the recent subsidence rate and patterns in the Nile Delta using the synthetic aperture radar Sentinel-1 data of 144 images obtained between 2015 and 2019, based on coherence small baseline subset interferometry of ~2900 interferograms. We distinguished three patterns of deformation due to three different physical mechanisms: 1) The land subsides with rates ranging from -12 to -20 mm/year in major cities (such as Zagazig, Mit Ghamr, Tanta, Mansoura and Mahla) due to urban-induced loading; 2) A subsidence rate ranges between -3 and -8 mm/year along the coastal margins due to natural sediment dewatering and compaction. This rate is consistent with the global positioning system rate of -3.5 mm/year and 3) A subsidence rate ranges from -20 to -16 mm/year and -6 to -12 mm/year in newly reclaimed lands on the west and east of the delta's flood plains, respectively, due to groundwater overexploitation. Our findings, in contrast with results from previous studies of regional deformation mainly felt to be controlled by natural processes, demonstrate a localized subsidence and predominant anthropogenic control on the land deformation and call for revisiting sea level rise-related flooding models in the Nile Delta. In light of the new findings, the authorities should take necessary measures to reduce the ongoing land subsidence through enforcement of urban planning policies in the delta's flood plain and development of a sustainable management strategy for groundwater extraction.