An Earth Observation
Approach towards Mapping
Irrigated Areas
and Quantifying Water Use by Irrigated Crops in South Africa
WRC Report TT 745/17
Dr Gerhard Backeberg
Executive Manager: Water Utilisation in Agriculture
Water Research Commissio n.
T
he estimations of the area of irrigated
crops are currently outdated and vary
greatly. Various assessments since 1990
documented the area under irrigation,
using different approaches. According to these
estimates, the area under irrigation ranged
between 1.21 to 1.58 million ha and the area
registered for irrigation was between 1.44 to
1.68 million ha. To address the knowledge gap
regarding the appropriate methodology and
obtaining recent empirical evidence of the
irrigated area, a research project was initiated
by the Water Research Commission (WRC) in
2013, which was co-funded by the Department
of Agriculture, Forestry and Fisheries
(DAFF). The overarching aim of this research
project, led by Prof Adriaan van Niekerk of
Stellenbosch University (SU), was therefore
to update the existing estimations of the
area and amount of water used by irrigated
agriculture in South Africa (SA). As stated in the
published WRC report, the project by SU was
undertaken with national and international
partners.
Remotely sensed earth observation (EO) data
are regularly captured from a wide variety
of aerial and satellite platforms. The wide
coverage and cost-effective nature of EO
images are not only ideal for determining the
AgriKultuur |AgriCulture
area under irrigated agriculture but have for
many years been employed in energy balance
modelling to provide up-to-date estimates
of actual evapotranspiration (ET) and the
total amount of water utilised by irrigated
agriculture.
A literature review of existing methods
confirmed that EO is the only viable approach
to use for national assessments. This
research consequently applied various EO
and geographical information systems (GIS)
techniques, including the mapping of irrigated
agriculture and the modelling of actual ET.
Monthly datasets of ET for a 12- month period
was generated for the entire SA. The ET
datasets describe the water consumption and
crop production on land between 1 August
2014 and 31 July 2015 and thus capture the
phenology of vegetation, crop production
cycles and associated water consumption in
SA. The generation of the irrigated area map
and the calculation of the total water use
by irrigated crops were informed by these
datasets.
The ETLook model used to produce the
monthly ET dataset proved robust despite
some challenges with available and accurate
(spatial) rainfall data. The irrigated area map
generated using the ET dataset – along with
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