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Spate irrigation is a type of water management unique to arid regions bordering highlands. Spate irrigation systems are among the most fascinating and complex resource management systems. It is common in South Asia, the Middle East, North Africa and the Horn of Africa. . Spate irrigation systems are generally situated in remote areas where there is deep-seated poverty and support systems are weak. Spate irrigation is an ancient form of water management, involving the diversion of flashy spate floods running off from mountainous catchments, using simple deflectors of bunds constructed from sand, stones and brushwood on the beds of normally dry wadis. This type of agriculture is very risk-prone and requires high levels of co-operation between farmers to divert and manage the distribution of flood flows.

Uncertainty is a defining characteristic. The number and sequence of floods vary from one year to another. So do yields, which can be high however.
A second important characteristic is that sedimentation is as important as water management. Rivers in spate lift and deposit huge quantities of sediment. As a result there is constant change in bed levels, in both the river system and the distribution network. The uncertainty, occurrence of high flood peaks and heavy sedimentation mean that conventional irrigation modernization approaches are inappropriate.

Sudden floods, or spates, originate from sporadic rainfall in macro catchments. After the land is inundated, crops are sown – sometimes immediately, but often the moisture is stored in the soil profile and used later. Spate irrigation systems support farming systems – usually cereals and oilseed, but also cotton, pulses and even vegetables.

Examples.

The largest area under spate irrigation is in Pakistan (1,402,000 ha). There are also substantial areas in Somalia (150,000 ha), the Sudan (146,000 ha), Yemen (115,000 ha) , Algeria (110,000 ha), Ethiopia (100,000 ha) and Morocco (79,000 ha).