Environmental monitoring and change assessment of Toshka lakes in southern Egypt using remote sensing

The High Dam in Aswan was designed so that if the water level behind the dam approaches 178 m above the sea level, surplus water should be diverted naturally toward the Toshka depression in the Western Desert of Egypt. The objective of this study was designed to map the spatial extent of temporal changes that occurred as a result of the formation of Toshka artificial lakes west of the Nile Valley from 2000 to 2013 using the Moderate Resolution Imaging Spectroradiometer (MODIS). A group of spectral transforms have been examined to extract the surface area of water in the lakes as revealed in 14 MODIS images on the basis of one image per year. The Land Surface Water Index, the Normalized Difference Vegetation Index (NDVI), and the new Normalized Difference Lake Index (NDLI) were operated. Results showed that the NDLI was the best to eliminate spectral interferences from surrounding non-water objects. The lakes, which approached their maximum surface area in 2002 have experienced considerable diminishing and are expected to eventually disappear due to evaporation. Salinization and sand encroachment were observed in satellite data at areas, which were previously inundated by water. MODIS images have proved that they could afford an efficient and sustainable source of remotely sensed information for monitoring water bodies in hyper-arid deserts.