| Summary: | One of the major challenges facing Egypt is limited water resources associated with rapid increase in population. In 1960s, Egyptian government started to use groundwater from the Nubian Sandstone Aquifer System (NSAS) in the Western Desert to expand agricultural sector. Siwa Oasis is the focus of this study to assess the efficiency of groundwater use and corresponding impacts from 1980 to 2012. Results show that from 1980 to 1998, withdrawal from poorly designed wells increased rapidly causing an increase in excess water about 336%. The increase of excess water with the usage of poor drainage produced lakes. Remote Sensing showed in 2000, there were 21,348 acres of lakes with an increase of 89% since 1987 due to unmanaged withdrawal. After management intervention, excess water decreased about 94.7% from 1998 to 2012 causing a decrease in lakes area by 24%. Groundwater electrical conductivity (EC) increased from 4.5 to 10.5 ds/m in 1996 and 2013, respectively. Yields of olives and date palms decreased about 46% and 55%, respectively from 2000 to 2011 resulting in net revenue decrease of more than 60%. Results show that salinity has a strong negative correlation with yield and net revenue. Findings showed the importance of developing a meaningful groundwater resources management plan for Siwa region. Keywords: Nubian Sandstone Aquifer System, Siwa, Water use efficiency, Remote sensing, Salinity, Groundwater management
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