The deserts of Egypt used to be a fertile green valley until they over used the water in it. (other issues involved but that was a main one)
EDIT: Egypt has always been in a desert(not always, but much of human history), The Nile River valley was once a fertile green valley.
This couldn't have anything to do with the interruption of the flood cycles due to daming the nile could it? (hint: it does). The nile used to flood and during the floods silt would be deposited on the river banks making them fertile soils instead of sand. Dams have stopped these floods to control the river (read that as not allowing the river to wipe out everything on its banks during yearly floods). So without yearly floods, there is no sediment deposited, thus no fertile soils to be green. Not much grows in sand due to the sand having a poor capacity to hold water. Sand is a great growth medium, with the exception that it require extremely high water usage (not large doses of water, but small increments of water everyday or multiple times a day according to infiltration rate and evaporative transpiration). So basically, it's not the lack of water, its the lack of sediments deposited