Sustainable use of irrigation water, water footprint and virtual water in advancing transboundary water policy in the Nile Basin countries
No Thumbnail Available
Date
2020-07
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
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 estimating 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 evaluate deficit irrigation management and
its impacts on yield and water productivity of barley; second, evaluating of the blue water-saving
potential through deficit irrigation and mulching; 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 crops in the Nile Basin countries. For the case
study, the barley has been selected as a target plant for multiple reasons. Firstly, barley is the
fourth most important annual cereal crop grown globally; secondly, the crop grows under a
different agro-ecological zone; thirdly, barley is both irrigated and rain-fed crop and commonly
cultivated across upstream and downstream countries. To determine the irrigation amount of
barely, the irrigation field experiment was arranged in a 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 reason
for the application of less water to provide a better yield might due to, Kc value, soil, and the
regional crop variety respond well to water stress. 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 at a spatial resolution of 5x5 arc-minute grid cells for the year
1986-2015 based on 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 per crop, 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
Page VII
maize (6046m3
/tonne), rice (5175m3
/tonne), sorghum (2644m3
/tonne), and millet
(2160m3
/tonne) and in Egypt, groundnut (3138m3
/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-saving; WF of crops and virtual water trade across the Nile
Basin countries. Water-scarce countries like Egypt and Sudan can increase imports of waterintensive 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
Sustainable, water use, water footprint, virtual water, water policy, Nile Basin countries