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for the project might not be representative
of the current or longer term situation?
‘Our main expected outcome is to develop
the methodology and choosing a refer-
ence year was basically just to test it,’ says
Dr Jarmain. ‘There will always be years that
are drier or wetter in different areas, but
the idea is to repeat the process regularly
and over time you’d get a better sense of
what is happening in an area. Automating
the process would allow the information to
be updated and made available in near real
time. Ideally, a web portal could be set up,
where maps could be viewed of crop water
use on a monthly basis. The 2014 to 2015
map will be used as a baseline for compara-
tive purposes.’
This would not only facilitate better moni-
toring of water use, but would also assist
managers in taking decisions on possible
expansions in irrigated agriculture. One
of the project’s aims is to show how the
methodology can be combined with a water
accounting framework to assess the water
available at different scales.
‘For an individual catchment, if we know
how much water we have from rainfall
and how much is used for irrigation, plus
we know of other water extractions taking
place and we know what the environmen-
tal requirements are, we can get some idea
of whether this is a vulnerable catchment,’
says Dr Jarmain.
‘If it’s on the negative side of the balance
sheet and there’s clearly no water, the man-
agers could start looking at how the water
has been allocated, and it should be a no-
go sign for any new developments. But if it’s
on the positive side, it would indicate that
there is at least a chance for new alloca-
tions, requiring more detailed investigation.
’The project is managed by Dr Gerhard
Backeberg (executive manager: Water Uti-
lisation in Agriculture, WRC) who reiterates
that the main purpose of the research is to
establish the baseline of the area irrigated
and actual evapotranspiration crop water
use with application of satellite imagery.
‘The project is due for completion in March
2018 and the report published by the
middle of next year,’ he says. ‘The informa-
tion generated with this modelling ap-
proach should in future be operationally
implemented and updated on preferably a
monthly basis. Refinement with additional
research and development is also required.’
This includes, for example, comparing the
area irrigated with suitability of soils for ir-
rigation, investigating water application in
relation to actual evapotranspiration crop
water requirements, analysing irrigation
type (permanent, supplementary or occa-
sional) and methods (surface, sprinkler or
micro/drip), evaluating the lawfulness of
water use and assessing the scale of irriga-
tion schemes.
The Wide-Scale Modelling of Water Use
and Water Availability with Earth Obser-
vation/Satellite Imagery project is being
carried out by Stellenbosch University, in
partnership with eLEAF®, Agricultural Re-
search Council, GeoTerra Image® and inde-
pendent consultants.
To contact the project team, email Dr Caren
Jarmain at
cjarmain@gmail.com .