SABI Magazine Volume 9 Issue 4 | Page 9

Research
Estimates of the area under and
water used by irrigated crops
are both outdated and vary
greatly. Recent estimates of the
actual area under irrigated crops
range between 1 252 601 ha 1 and
1 350 000 ha 2 . The Van der
Stoep and Tylcoat 1 estimate is
based on the WARMS database,
which recorded the registered
area under irrigation in 2014,
as 1 440 748 ha. The 1990
estimate of 1 290 132 ha by the
Committee on Food and Feeding
strategy 1990 3,4, is still considered
as the last authoritative empirical
estimate of the actual area
under
irrigated
agriculture
in South Africa.
Water
use
by
irrigated
agriculture was estimated to be
10 740 million m 3 /year in 1996
(as part of the “Overview of
Water
Resource
Availability
and Utilization in South Africa”)
and 7 836 million m 3 /year in
2000 (as part of the “National
Water
Resources
Strategy
(NWRS)”) 5 . Note that the latter
estimate is based on a 98%
assurance of supply.
©
With many relevant water resources
related questions in mind, current
research jointly funded by the
Water Research Commission
(WRC) and the Department of
Agriculture, Forestry and Fisheries
(DAFF) hopes to shed light on
the current extent of irrigated
agriculture in South Africa as
well as the consumptive water
use. In this article some research
findings are shared.
PROVISIONAL
NOT FOR
REPRODUCTION
Earth observation approach
A novel approach is being
developed to routinely update
outdated estimates related to
South African irrigated agriculture.
Earth observation and geospatial
data provide an independent
and objective data source for
assessing
water
resources.
Such data sets, in combination
with sophisticated biophysical
modelling and machine learning
algorithms, are being employed
in an innovative way to map
irrigated areas and to estimate
the actual water consumed by
irrigated agriculture. In the WRC-
DAFF funded research all fields
actively irrigated (permanent,
©
©
PROVISIONAL PROVISIONAL
NOT FOR
REPRODUCTION NOT FOR
REPRODUCTION
Figure 1: Water use (actual evapotranspiration, ET) for 2014/15 (1 August
2014 to 31 July 2015) for the entire South Africa (top), Western Cape
(bottom left) and Mpumalanga provinces (bottom right).
supplementary or occasionally)
during the period 1 August 2014
to 30 July 2015 are accounted
for. Previously irrigated areas or
fallow fields are also mapped,
but as a separate class and
are not considered in the water
use calculations for the period
of assessment.