Water overflowing normally dry land is among the deadliest natural hazards on record and, paradoxically, the force that enabled the first civilizations. The Nile's annual flood, and the wilder floods of the Tigris-Euphrates and Yellow River, deposited the fertile silt that fed the first states. The toll falls hardest on the poorest, who occupy the cheapest floodplains, and deforestation and paved cities turn ordinary rain into catastrophe. Levees and dams offer control but backfire when they fail, and climate change is making extreme floods more frequent.
The same water that drowns also feeds. A river bursting its banks is among the oldest and most universal of disasters, and across recorded history flooding has killed more people than almost any other natural force. Yet the world's first cities rose on exactly that danger. Year after year the Nile's flood — and the wilder, less regular floods of the Tigris, Euphrates, Indus, Yellow River, and Ganges — spread fresh fertile mud across the land, and that silt fed the harvests that fed the first states. Civilization was built on the floodplain because the floodplain was where the soil was richest. The flood gave with one hand and took with the other, and it has never stopped doing both.