Sustainable and efficient irrigation water use, water footprint and virtual water to advance water policy in the transboundary Nile Basin
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Date
2020-06
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Addis Ababa University
Abstract
The world faces a huge challenge in balancing water demand for the growing populations and
economic development, while protecting the environment with declining freshwater supply.
Deficit irrigation (DI) and organic mulching (OM), understanding the water footprint (WF) and
virtual water will play a key role in sustainable water management in water scarce regions. The
main objective of the study is to provide policy relevant information by assessing the virtual
water flows and water footprint of major crops produced in the Nile Basin. The research consists
of four main components: first, a case study aimed to determining the depth of irrigation and its
effect on the yield and water productivity of barley; second an assessment of the blue watersaving potential through DI and OM; third, a spatial analysis of the WF of major crops in the
Nile Basin; and, finally, an assessment of the annual variability and long-term changes in WF and
virtual water flow of selected major crops in the Nile Basin countries. To determine irrigation
depth of barely, the irrigation field experiment was arranged in randomized complete block
design (RCBD) with four replicates and five irrigation treatments (fully irrigated treatment (FIT),
90% FIT, 85% FIT, 80% FIT, & 75% FIT). The AquaCrop model & the global WF accounting
standard were used to calculate the WF of crops. For barley production at 80% FIT, the largest
yield was recorded at 1700 kg/ha. The provision of a certain level of water stress (80% FIT)
throughout the growing season, translates to a better yield relative to full irrigation. The FIT
(2.01 kg/m3
) and 80% FIT (2.95 kg/m3
) treatments had the lowest and highest water
productivity, respectively. The finding indicates that barley production using DI offers great
potential in improving water use. The blue water-saving potential of DI and OM, the spatial and
temporal variability of WF, was modeled using the AquaCrop-OS plugin model at a spatial
resolution of 5x5 arc-minute grid cells for the year 1986-2015 on the basis of a global data
source. The blue WF of the selected crops was highest in Egypt, Sudan, South Sudan, and
Tanzania. For the current situation, the total blue WF was 48.5 km3
/y, 89% of which falls in
Sudan (55%) and Egypt (34%). Production of sorghum account for the largest share of the blue
WF (50%) followed by maize (21%), and rice (16%). DI combined with OM showed to reduce
the current blue WF by as much as 42%. Egypt and Sudan exclusively rely on irrigation water
while the rest are based on rainfed in which other countries need to use irrigation for better
production. Rainfall and evapotranspiration are highly variable in all production regions, which
are the main drivers affecting the availability and distribution of water resources. Likewise, the
findings show that there is a substantial difference in green and blue WF among crops across the
Basin countries. The largest average blue WF (m
3
/y) in crop production was found in Sudan,
South Sudan, and Egypt. In Sudan, the crops with large WF are maize (6046 m
3
/tonne), rice
(5175 m
3
/tonne), sorghum (2644 m
3
/tonne), and millet (2160 m
3
/tonne) and in Egypt, groundnut
(3138 m
3
/tonne). Egypt is the largest exporter of rice with an average net virtual water export of
810 Mm3
per year followed by 19 Mm3
in Sudan and 16 Mm3
in Egypt for groundnuts
production. The results of this study have some relevant policy implications and may be of great
use in policy formulation. This research provided empirical evidence of the potential blue water
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saving; WF of crops and virtual water trade across the Nile Basin countries. Water-scarce
countries like Egypt and Sudan can increase imports of water-intensive crops from relatively
water abundant countries (upstream countries), and vice versa. It is important to know the
national virtual water trade with internal and external virtual water flows in order to establish a
sound national water policy. Virtual water trading can therefore help to sustain the water use of
the regions in a sustainable manner. It is therefore necessary to use evidence that satisfies the
various criteria for the design, planning and implementation of sustainable water resource
management.
Description
Keywords
Efficient irrigation water use, water footprint, virtual water, water policy, Nile Basin