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regions where the amount of evaporation largely exceeds rainfall. Therefore, an in
situ WH technique where rainfall is collected and stored directly into the soil profile
will be better (Abu-Zreig and Tamimi 2011 ). The MCWH system requires a large
area to collect water and its construction requires more labor. Increased withdrawals
of water in rainfed and irrigated agriculture may have negative implications on
downstream water availability within a river basin scale, and this needs further
investigation (Rockström et al. 2010 ; Glendenning and Vervoort 2010 ). Ngigi
( 2003 ) stated that the impacts of an RWH system in Ethiopia, Kenya, Tanzania and
Uganda were still marginal because the adoption rate is low despite the success of a
number of RWH systems.
9 Implementation and Operational Management
of Rainwater Harvesting Systems
There is historical evidence that rainwater harvesting has been an important element
of community development since the beginning of human settlements. Many cul-
tures have developed their societies with the primary management of water resources
as a cornerstone, developing more sophisticated ways of supplying water both for
consumption and agriculture (UNEP-SEI 2009 ).
Rainfed agriculture is practiced on 80 % of the world’s agricultural land area and
generates 65–70 % of the world’s staple food. For instance, more than 95 % of the
farmland is rainfed in Africa and almost 90 % in Latin America (UNEP-SEI 2009 ).
There are numerous positive benefits for harvesting rainwater. The technology is
low cost and highly decentralized which empowers individuals and communities to
manage their water. WH has been used to improve access to water and sanitation at
the local level. In agriculture, rainwater harvesting has demonstrated the potential to
double food production by 100 % compared to the 10 % increase from irrigation.
At the global level, there is no comprehensive assessment of the extent of imple-
mentation of rainwater harvesting technologies for specific uses. Nor is there any
summarized information on how much land is currently under any type of in situ
rainwater harvesting. For the specific application of conservation tillage, as no-
tillage agriculture, national statistics have been aggregated by Hobbs et al. ( 2008 ).
Their information suggests that, globally, only a small fraction of the land surface,
about 95 million hectares, is currently under conservation or no-till agriculture. For
irrigation and conservation tillage, the AQUASTAT database (AQUASTAT 2009 )
holds data for a selected number of countries. Unfortunately, the information on
irrigation cannot directly be associated with rainwater harvesting systems for irriga-
tion purposes as it differentiates between surface water and groundwater, which
does not allow the separation of shallow groundwater from deep groundwater or
surface water withdrawn from ʻblueʼ water sources (lakes, waterways, large dams)
from small-scale systems. The recent assessment of irrigated and rainfed land, com-
pleted in the Comprehensive Assessment of Water Management in Agriculture (CA
A. Yazar and A. Ali