Monitoring Spatio-Temporal Changes in Vegetation Cover, Soil Salinity and Waterlogging in Siwa Oasis, Egypt Using Remote Sensing Data and Techniques رصد التغيرات المکانية والزمانية في الغطاء النباتي وملوحة التربة والغدق بالمياه في واحة سيوة ، مصر باستخدام بيانات وتقنيات الاستشعار عن بعد

The availability of groundwater resources makes Siwa Oasis a potential region for agricultural projects in the western-desert of Egypt. This region, however, faces serious environmental problems such as water-logging and consequently soil salinization. Accordingly, the primary objectives of this research were to monitor and evaluate spatio-temporal changes in vegetation cover, water-logging and soil salinity in Siwa Oasis using remote sensing (RS) data and techniques. Therefore, Landsat images were acquired at four different periods (1986, 2000, 2013 and 2019), pre-processed and analyzed. Three spectral indices were used for studying the spatio-temporal changes in the mentioned land covers. These indices are the Optimized Soil Adjusted Vegetation Index (OSAVI), the Normalized Difference Water Index (NDWI) and the Salinity Index (SI). The obtained results indicated that the studied land covers were predicted at higher accuracy. Vegetated lands were increased from 19.64 km² in 1986 to 94.58 km² in 2019. Water-logging areas also increased from 19.42 to 57.00 km2 during the same period. However, sabkha areas decreased from 32.96 to 28.32 km². The increase in water-logging areas could be attributed to the increase in vegetated lands, use of inefficient irrigation systems and poor drainage in the closed depression.  This, in turn, affects the residential buildings in the Old City as well as the agricultural lands in the low-lying areas of the Oasis. In conclusion, Siwa Oasis is in urgent need for developing an effective land management program, which should be taken into account using more effective irrigation systems and enhancing agricultural drainage in the area.