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(i.e., storm flow in larger gullies). Storage systems collect runoff water at different
scales from field to catchment scale in various types of structures or in the soil for
supplemental irrigation (Rockström 2002 ; Oweis and Hachum 2006 ).
The goals of water harvesting are summarized by Prinz ( 1996 ) as:
- Restoring the productivity of land which suffers from insufficient rainfall
- Increasing yields of rainfed farming (dry farming)
- Minimizing the risk of crop failure in drought-prone areas
- Combating desertification by tree plantation
- Supplying drinking water to humans and animals.
In regions with annual precipitation between 100 and 700 mm, low-cost water
harvesting may provide an interesting alternative if irrigation water from other
sources is not readily available or is too costly. In summer rainfall areas, the mini-
mum precipitation for WH is around 200 mm year–1. In areas with more than 600–
700 mm annual rainfall, WH can prolong the cropping season. In comparison to
pumping water, water harvesting saves energy and maintenance costs. These advan-
tages are countered by the problem of unreliable rainfall, which can partly be over-
come by interim storage. Modern hydrological tools (e.g. calculation of rainfall
probability and water yield) allow more precise determination of the catchment area
(Prinz 2002 ).
WH supports a flourishing agriculture in many dry regions where rainfall is low
and erratic in distribution (Oweis et al. 1999 ; Oweis et al. 2001 ; Ali et al. 2010 ).
Water harvesting is particularly advantageous in the following circumstances:
- In a dry environment where low and poorly-distributed rainfall normally makes
agricultural production impossible. Provided other production factors such as
soils and crops are favorable, WH can make farming possible even in the absence
of other water resources. - In rainfed areas, where crops can be produced but with low yields and a high risk
of failure. Here WH systems can provide enough water to supplement rainfall
and thereby increase and stabilize production. - In areas where water supply for domestic and animal production is not sufficient.
These needs can be satisfied with WH. - In arid land suffering from desertification, where potential production is dimin-
ishing due to lack of proper management. Providing water to these lands through
WH can improve the vegetative cover and help to halt environmental degradation
(Prinz 1996 ; Rockström 2002 ).
The specific benefits listed above lead to many other non-tangible and indirect
socioeconomic gains. These include stabilization of rural communities, reduced
migration of rural people to cities, use and improvement of local skills, and improve-
ment in the standard of living of millions of poor people living in the drought-
stricken areas (Prinz 1996 ; Rockström 2002 ; Mekdaschi and Liniger 2013 ).
The main components of a WH system include catchment area, storage facility
and the target area (Fig. 1 ; Oweis et al. 2001 ) as described below:
A. Yazar and A. Ali