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Al die ondersteuning
om water effektief
te gebruik.
GWK
Besproeiing
GWK besproeiing staan gereed om boere te ondersteun in:
•Die ontwerp van nuwe stelsels (spilpunt, mikro, drup en sprinkel)
•Die evaluering van bestaande besproeiingstelsels
•Doeltreffende waterbestuur (spuitpakkette, watermeting en
die optimalisering van bestaande stelsels)
Matthys Saayman
Tegniese Bestuurder: Besproeiing
053 298 8318
matthyss@gwk.co.za
The ETLook model used to produce the monthly evapotranspira
tion dataset proved robust despite some challenges with available
and accurate (spatial) rainfall data. The irrigated area map generated
using the evapotranspiration dataset – along with other remotely
sensed data – was judged highly accurate by participating stake
holders. All known misclassifications were manually corrected to
produce the final, validated third version of the map.
According to the map 1 334 562 ha of South Africa’s land surface
was actively irrigated during 2014/2015. This constituted about
10% of the total area under cultivation (including fallow areas) of the
area used for agriculture in 2014/2015. Western Cape had the highest
area (260 476 ha) under irrigation, with Limpopo having the second
largest area under irrigation (218 302 ha).
The national aggregation of evapotranspiration for all irrigated ar
eas in 2014/2015 showed that the total consumptive water use from
irrigated agriculture in South Africa was 10 221 million m
3
per
year. This compares well with previous estimates such as the 1997
Overview of water resource availability and utilisation in South
Africa
, which estimated the water use by irrigated agriculture to
be 10 740 million m
3
per year.
It is known that South Africa has a limited availability of suitable
land and adequate water resources for irrigated crop production.
With the added pressures of climate change, population growth and
decline in water quality, the need for improved assessments of the
current water resources and land use is critical.
Actions related to improved water use efficiency (WUE) and
irrigation expansion can only follow once this information is avail
able. This project and report have contributed recent and accurate
information on water use by different irrigated crops over time (i.e.
throughout the growing season) and space (i.e. in different geo
graphical areas). Combining these datasets into a water accounting
(WA) framework will improve understanding of the actual pressures
on South Africa's water resources with changes in land use, that will
better inform water use for irrigated agriculture.
In summary it can be stated that the knowledge gap has been closed
by applying Earth Observation methodology that is at the forefront
of international research practice. Breakthroughs through research
have therefore been made by providing practically relevant knowl
edge which is of high priority. In this regard the report gives an excel
lent overview of the status quo of irrigated agriculture water use for
the period of 1 August 2014 to 31 July 2015.
It must again be emphasised that the study established a meth
odology that can be replicated for other periods. Thereby it gives
competitive advantage to DAFF for further implementation of avail
able research results which have been created by SU through fund
ing by the WRC and DAFF.
Taking these innovative research results and demonstration of ap
plication forward to practical implementation, a number of issues
have to be considered: First, it is unlikely that the irrigated area
mapping (IAM) and water use quantifications produced in this pro
ject are representative of the long-term situation. The application of
the methodology to other periods is essential in supporting sound
water management practices and guiding decisions about changes
in water use allocations.
Second, the FAO recently released an Africa-wide, freely available,
monthly open access of remotely sensed derived evapotranspi
ration dataset at 250 m resolution (also generated using the
ETLook model and thus very similar to the evapotranspiration
dataset used in this project) for the period 2009 to 2019. This will
considerably reduce the cost of future implementation in
South Africa. Linked with the recently released and freely avail
able Sentinel 2 imagery, the evapotranspiration datasets available
through the FAO will allow for the production of seasonal (even
monthly) IAMs and water use quantifications up to 2019.
Third, if the irrigated area mapping process is automated, the
latency (period required for production) can be reduced to a few
weeks, which will substantially increase the reliability of the water
use estimations, as it will allow for local validation to be carried out.
Finally, based on the findings of this research, it is mainly recom
mended that:
The irrigated area mapping procedure is automated and funding
for implementation of the procedure by DAFF is prioritised.
The irrigated area map is continuously (i.e. on a monthly or
quarterly basis) updated.
Consumptive water use of irrigated crops is revised on a continu
ous (seasonal) basis at national scale.
The water accounting framework is applied on primary catch
ment level, preferably in all catchments of South Africa.
For more information contact the author at
gerhardb@wrc.org.za
.
Focus
Irrigation
34
Estimating
irrigated area and water use