THE RISE AND DEMISE OF THE NEW LAKES OF SAHARA

We have used multi-temporal resolution Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) (September 1998 and April 2007), Digital Elevation Models (DEMs) extracted from the Shuttle Radar Topography Mission (SRTM), and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data to examine the New Lakes of Sahara in southern Egypt and their geomorphological and geological controls. These lakes appeared in September 1998 when water spilled northwestward towards Tushka Depression as a result of water level rise in Lake Nasser induced by above-average precipitation in the Ethiopian Highlands. Five new lakes were formed in local depressions underlain by an impermeable Paleocene Shale and Chalk formation where water infiltration is insignificant. Our work has shown that: (1) The progression of the lakes went through three stages: (a) a rise stage between September 1998 and August 2001 where the area covered by the lakes reaching a maximum of ~1586 km2. This stage is dominated by water supply that far exceeded evaporation rate in Sahara (2.3 m/year). The rise stage is divided into an early sub-stage between August 1998 and August 1999 where area covered by the lakes increased by ~75 km2/month. This was followed by a late sub-stage between August 1999 and August 2001 where area increased averaged ~28 km2/month. (b) A steady-state stage in which the area covered by the lakes remained relatively unchanged. This stage occurred between August 2001 and August 2003 in which water lost through evaporation was continuously replaced by supply from Lake Nasser. (c) A demise stage between August 2003 and April 2007 in which water supply from Lake Nasser completely stopped and water was continuously evaporating from the lakes. During this period, the area covered by the New Lakes of Sahara decreased from ~1535 km2 to ~800 km2 with an average loss of ~17 km2/month. (2) The New Lakes of Sahara will completely disappear by March 2011 if the water supply and evaporation rate conditions remained the same. (3) Spatial distribution of the New Lakes of Sahara is strongly controlled by morphologically-defined E-, N-, NE-, and NW- trending faults. We further suggest that water recharge of the Nubian Aquifer by the New Lakes of Sahara was insignificant since much of the lakes were spread above an impermeable formation.