Irrigation Agriculture. Egypt's prosperity was founded upon irrigation agriculture. The surplus food that farmers produced supported the bureaucracy, priesthood, artists, and royal family. When the Nile flood brought new topsoil to the river valley and enough water to fill the irrigation canals, Egypt was stable and prosperous. When the Nile flood failed for long periods, the central government and all the activities that government supported collapsed.

Desert and River Valley. The Egyptian desert and river valley have two distinct climates. The desert's climate depends on local rainfall, while the moisture level in the valley depends entirely on the water that the river brings from its source, the monsoon rains in Ethiopia.

Rainfall Levels. Local rainfall levels in the desert fluctuated within a narrow range during ancient Egyptian history. Yet, even small increases in rainfall made life possible in the oases of the Sahara. Bundles of leaves...