I cite the following post that I've pasted below... 1.5 Liters is what he says: Obada Barry, DMD.
Seasons have a much greater impact in the interior. In the Sahara Desert, summer temperatures often exceed 104ÂºF/ 40ÂºC in summer, but may fall to near freezing during winter nights. In terms of rainfall, the northern part of Morocco is considerably wetter than the arid south (especially along the coast).
There are more than 500 plant species in the Sahara desert. Most of these plant species would be near the Nile. There are certain parts such as the Nile valley that are quite luscious and green but other than that, the Sahara is very barren and plain.