Well The Nile River flooded annually; this flooding was so regular that the ancient Egyptians set their three seasons Inundation, or flooding, Growth, and Harvest around it.
This annual flooding was vital to agriculture because it deposited a new layer of nutrient-rich soil each year. In years when the Nile did not flood, the nutrient level in the soil was seriously depleted, and the chance of food shortages increased greatly. Food supplies had political effects, as well, and periods of drought probably contributed to the decline of Egyptian political unity at the ends of both the Old and Middle Kingdoms.
