Spate irrigation is the art and science of water management that is unique to semi-arid environments. It is found in the Middle East, North Africa, West Asia, East Africa and parts of Latin America. Flood water from mountain catchments is diverted from river beds (wadis) and spread over large areas. Spate systems are very risk-prone. The uncertainty comes both from the poorly predictable nature of the floods and the frequent changes to the river beds from which the water is diverted. It is often the poorest segments of the rural population whose livelihood and food security depends on spate flows. Substantial local wisdom has developed in organizing spate systems and managing both the flood water and the heavy sediment loads that go along with it.