Pressures affecting freshwater systems and
resources in
South Africa: #1
The characteristics of South Africa's aquatic ecosystems are largely determined by the interaction between climate, rainfall and the
landscape over which water flows (see Introduction to this report -
figures on general characteristics of country). For South Africa,
the warm Agulhas current on the east coast, the cold Benguela
current on the west, coupled to the topography of the sub-continent,
have created an overall theme of aridity (Preston-Whyte and Tyson,
1988). Climatic features affecting South Africa's aquatic
environment include (from Walmsley, 1991):
- low precipitation- with an average
rainfall of 497 mm, the country is well below the world average
of 860 mm.
- high temporal climatic variability with
distinct seasonal rainfall patterns (see Climate and Atmospheric Change section).
- high spatial climatic variability - the
country has six rainfall regions with higher rainfall occurring
on the East coast, and the country becoming progressively more
arid towards the West (see Introduction).
- high solar radiation due to a low
degree of cloudiness.
- high evaporation rates - except for small areas on the coast and certain
escarpments, evaporation exceeds rainfall (see
Introduction).
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- Figure 3.2 plots mean annual precipitation (MAP) against mean annual evaporation (MAE) for the major South African catchments. Evaporation exceeds
precipitation in all cases.
- severe and prolonged
droughts which are often terminated by severe
floods. During any one season certain areas may
experience drought whereas others experience severe flooding.
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| Figure 3.2 Mean annual precipitation and evaporation |
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Region 1: A
sub-tropical coastal plain incorporating the
Eastern Transvaal lowveld, Mozambique and
northern KwaZulu/Natal, in which the marine
influence is strong, and aquatic ecosystems have
variable salinity.
Region 2: The summer
rainfall region of the highveld and south eastern
coastal plain, incorporating Gauteng, the Northwest
Province, the Free State, southern KwaZulu/Natal and the
northern section of the Eastern Cape. The Vaal-Orange,
Tugela and Limpopo rivers are all included in this
region.
Region 3:
The alpine mountain region of Lesotho. This area experiences high
rainfall, and is characterised by clear mountain
streams.
Region 4: The western and
southern Cape Mediterranean climate region. This area is
one of winter rainfall. It has temperate, unbuffered,
acid waters, arising principally from the Table Mountain
Sandstone in the mountainous regions. Marine influences
in the low-lying areas increase the buffering capacity
of waters and raise the
pH. There are two types of
waters: the "peat-stained" acid waters
draining the seaward slopes (e.g. the Steenbras, Palmiet
and Storms rivers), and the colourless acid waters
draining from the land-facing slopes (e.g. Olifants,
Great Berg and Breede rivers).
Region 5: The arid western
region stretching north from inland of Port Elizabeth
into Namibia and southern Botswana. The western part of
this region is dry, waters are temporary, alkaline and
carry very high dissolved solids and sediment loads. The
eastern section is characterised by short steep,
geologically young rivers with permanent flows, neutral
to alkaline waters and moderate levels of dissolved
solids.
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Population growth (see Social Dimensions section), increased economic
activity (see Economic Dimensions section) and changes in land use (see
Terrestrial Ecosystems section) all lead to increased water demand. Sectoral water
requirements in South Africa are presented in Table 3.1.
There is an estimated overall increase in demand of 51.7% over the
next 30 years. The environment is presently the smallest sector, and
only changes by 7.5% compared with the estimated increase of the
urban and domestic sector to almost three times the present day
usage.
| Sector |
% Contribution
to GDP* |
1996
(106 m3 a-1)
|
2030
(106 m3 a-1) |
Percentage
increase |
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Urban & domestic |
- |
2 171 |
6 936 |
219,5% |
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Mining and industrial |
37% |
1 598 |
3 380 |
111,5% |
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Irrigation &
afforestation |
6% |
12 344 |
15 874 |
28,6% |
|
Environmental |
- |
3 932 |
4 225 |
7,5% |
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TOTAL |
- |
20 045 |
30 415 |
51,7%
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Figures for water use
efficiency for each sector are not
available, but agriculture is considered to be the
least efficient in economic terms (production per
m3) and commercial forestry the least
efficient in environmental terms.
Groundwater demand has also increased, from approximately 1 790
million m3 a-1 in 1980 to about 2 000 million
m3 a-1 today. Seventy eight per cent of this water is utilised by
the irrigation sector (Figure 3.4). The demand for water does not necessarily co-incide with the spatial
distribution of water. |
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| Figure 3.4 Groundwater use per sector |
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Figure 3.5 shows the availability of surface water per capita for South Africa.
This indicates that the country'surban and
industrialised areas (Cape Town, Port Elizabeth,
East London, Pietermaritzburg, Bloemfontein, Pietersburg, and Gauteng) are the most
water stressed, and will become more so as the
population increases and the demand for water in the
urban and domestic sector increases. |
| Figure 3.5 Availability of surface water per capita for South Africa |
Because of the spatial variability of water resources and the
scarcity of water throughout the country, in many catchments the
need for water exceeds the supply of water. In 1996 the water
requirements in the Vaal, Lower Orange, Sundays, Great Fish, Olifants
(Mpumalanga) and Crocodile/Limpopo rivers exceeded the amount of
water available (Figure 3.6).
This situation is likely to rapidly worsen, and by
2030 the Breede/Berg basin will be added to this list
and the discrepancies between water requirements and
available balance in the other water-scarce
catchments will become larger (Figure 3.6b). |
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| Figure 3.6 Water balance for major catchments in South Africa, 1996 |
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Information on the
abstraction of water from surface- and
ground-waters, coupled with return flows, gives an
indication of local water budgets. However, this
information is not readily vailable and is not
presented here.
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Figure 3.6b Water balance for major catchments in South Africa, 2030
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There is also information about Freshwater Systems and Resources in the following reports:
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Metropolitan reports:
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Affairs and Tourism. All Rights Reserved.
Site maintained by the Directorate Environmental Information and Reporting
Last update: October 1999
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