The Concept and Components of the System

The drier environments, "the steppe," or, as they are called in the Arab world, Al Badia, occupy the vast majority of the dry

Annual rainfall (mm)

Annual rainfall (mm)

Amount of supplemental irrigation (mm)

Figure 4 SI production functions for wheat in different rainfall zones in Syria. (Adapted from Oweis, 1997.)

Amount of supplemental irrigation (mm)

Figure 4 SI production functions for wheat in different rainfall zones in Syria. (Adapted from Oweis, 1997.)

areas. The disadvantaged people, who depend mainly on livestock grazing, generally live there. The natural resources of these areas are fragile and subject to degradation. Because of harsh natural conditions and the occurrence of drought, people increasingly migrate from these areas to the urban areas, with the associated high social and environmental costs.

Precipitation in the drier environments is generally low relative to crop requirements. It is unfavorably distributed over the crop-growing season and often comes with high intensity. It usually falls in sporadic, unpredictable storms and is mostly lost to evaporation and runoff, leaving frequent dry periods. Part of the rain returns to the atmosphere directly from the soil surface by evaporation after it falls, and part flows as surface runoff, usually joining streams and flowing to "salt sinks," where it loses quality and evaporates. A small portion of the rain joins groundwater. The overall result is that most of the rainwater in the drier environments is lost, with no benefits or productivity. As a result, rainfall in this environment cannot support economical dry farming like that in rain-fed areas (Oweis et al., 2001).

Optimal annual SI amount (m3/ha)

Figure 5 Optimal economical annual SI amount (m3/ha) in different rainfall zones in Syria. (Adapted from Oweis, 1997.)

Optimal annual SI amount (m3/ha)

Figure 5 Optimal economical annual SI amount (m3/ha) in different rainfall zones in Syria. (Adapted from Oweis, 1997.)

Water harvesting can improve the situation and substantially increase the portion of beneficial rainfall. In agriculture, water harvesting is based on depriving part of the land of its share of rainwater to add to the share of another part. This brings the amount of water available to the target area closer to the crop water requirements so that economical agricultural production can be achieved. Water harvesting may be defined as "the process of concentrating precipitation through runoff and storing it for beneficial use."

Water harvesting is an ancient practice supported by a wealth of indigenous knowledge. Indigenous systems such as jessour and meskat in Tunisia; tabia in Libya; cisterns in north Egypt; hafaer in Jordan, Syria, and Sudan; and many other techniques are still in use (Oweis et al., 2004). Water harvest ing may be developed to provide water for human and animal consumption, domestic and environmental purposes, and plant production. Water harvesting systems have three components:

1. The catchment area is the part of the land that contributes some or all of its share of rainwater to another area outside its boundaries. The catchment area can be as small as a few square meters or as large as several square kilometers. It can be agricultural, rocky, or marginal land, or even a rooftop or a paved road.

2. The storage facility is a place where runoff water is held from the time it is collected until it is used. Storage can be in surface reservoirs, in subsurface reservoirs such as cisterns, in the soil profile as soil moisture, or in groundwater aquifers.

3. The target area is where the harvested water is used. In agricultural production, the target is the plant or animal, whereas in domestic use, it is the human being or the enterprise and its needs.

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