| The climate of any place on earth is
mainly determined by its latitude, its position relative to the distribution of land and
sea, and its height above sea level. The climate and the weather associated with it
(precipitation, temperature and wind) have a major influence on all human activities.
Situated in the Southern Hemisphere, South Africa experiences summer from
October to February and winter from June to August. South Africa’s climate is largely
influenced by maritime air from the southern waters of the Indian and Atlantic Oceans. Two forms of weather are dominant in South Africa,
frontal and convectional. The weather experienced by the CMA is frontal in nature. As part
of the South Western Cape, the CMA enjoys a Mediterranean climate, with mainly wet winters
and hot dry summers. |
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| Contents of CONTEXTUAL INFO on the
Climate: |
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| Precipitation |
| The South Western Cape Region,
in which the CMA is located, receives 80% of its annual rainfall during winter from May to
September. Figure 1 shows the mean annual rainfall for the CMA for
the period 1992 to 1998. This rainfall is mainly cyclonic and orographic but very
occasionally thunderstorms do occur. The mountains to the east of the CMA are sometimes
snowcapped but the snow layer never persists throughout the winter. Common cloud
formations over the CMA are low-lying dark grey nimbostratus clouds and orographic clouds
that often cover mountain tops. |
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| Figure
1 |
Mean
annual precipitation for Cape Town International Airport (1958-1996) (Source: South
African Weather Bureau) |
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| The rainfall over the CMA is influenced by
the steep peaks in the Cape Peninsula mountain chain as well as the Helderberg and the
Hottentots Holland mountain range to the east of the CMA (see Map).
As a result the annual rainfall varies greatly within the CMA – from between 500 mm
and 1700 mm on the Cape Peninsula, to between 500 mm and 800 mm on the Cape Flats, and
ranging from 800 to over 2600 mm in the mountains to the east of the CMA. Cape Town
International Airport situated on the Cape Flats receives 554 mm p/a (South African
Weather Bureau, 1998). This variable rainfall gradient is a contributing factor to the
numerous and diverse habitats and plant and animal species (see Terrestrial Ecosystems). |
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| Temperature |
| The average daily maximum
temperature of the CMA is about 28° C in mid-summer and 17° C in mid winter. Figure 2 shows the mean annual temperature for the period 1992 to
1998. Due to the moderating influence of the sea, temperatures rarely fall below 0° C or
rise above 35° C. As with rainfall, temperature is also influenced by the topography of
the CMA (see Water: Table 1). Temperature can therefore
vary depending on micro-climatic conditions that exist. |
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| Figure
2 |
Mean
annual temperature (1958-1996) (Source: South African Weather Bureau) |
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| Prevailing winds |
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| Prevailing winds for the CMA are south-easterly and north-westerly. In the
summer, winds are almost exclusively southerly and result in the formation of orographic
cloud on Table Mountain. In winter north-westerly winds are frequent and often spell rainy
weather. Winds over the CMA can reach gale force. |
| Global Climate Change |
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Global climate change poses major problems for global weather patterns
including those influencing the CMA. Climate change is caused by anthropogenic factors
such as industrial activity, transportation of goods and people and the burning of fossil
fuels. These activities result in the production of greenhouse gases including carbon
dioxide. This has potentially far-reaching implications for fauna and flora in the CMA.
- Climate change could threaten pollination
biology interactions, germination, and change fire and rainfall regimes (Possingham, 1993;
Stange and Wong, 1993; Bazzaz, 1990; Keeling, 1995; van Wilgen et al, 1992).
- Melting of the ice shelves in Antarctica and
shrinking glaciers could lead to the destruction of species unable to adapt to the
consequent habitat changes and the potential rise in sea levels.
Extreme weather events such as floods and
droughts are caused by the El Niņo phenomenon that influences global atmospheric
circulation. This phenomenon, caused by changing sea temperatures, affects the location of
major bands of clouds over southern Africa, causing them either to be driven offshore or
onshore. |
(Source:
CMC, 1999) |
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