Rivers and lakes
South Africa has no significant natural lakes, but several artificial lakes are used mostly for crop irrigation. None of the country’s rivers are commercially navigable (except one) and most river mouths are unsuitable as harbors because large sandbanks block entry for most of the year.
The Orange River is South Africa’s largest river. Rising in the Drakensberg Mountains, it goes across the Lesotho Highlands and joins the Caledon River between the Eastern Cape and the Free State. Before it empties into the Atlantic Ocean, it forms the border with Namibia.Other major rivers include the Vaal, Breede, Komati, Lepelle (previously Olifants), Tugela, Umzimvubu, Limpopo and Molopo rivers.
The subtropical location, on either side of 30° S, accounts for the warm temperate conditions so typical of South Africa, making it a popular destination for foreign tourists.
The country also falls squarely within the subtropical belt of high pressure, making it dry, with an abundance of sunshine.
The wide expanses of ocean on three sides of South Africa have a moderating influence on its climate. More apparent, however, are the effects of the warm Agulhas and the cold Benguela currents along the east and west coasts respectively. While Durban (east coast) and Port Nolloth (west coast) lie more or less on the same latitude, there is a difference of at least 6° C in their mean annual temperatures. Gale-force winds are frequent on the coasts, especially in the south-western and southern coastal areas.
Rainfall in South Africa
The amount of water on earth is constant and cannot be increased or decreased, but it is unevenly distributed across the earth. South Africa receives an annual rainfall of 450- 492 millimetres whereas the rest of the earth receives 985 millimetres. This is nearly half the earth’s average.
Thus South Africa is classified as a semi-arid country. There is also uneven distribution of rainfall across South Africa. The eastern half of the country is much wetter than the western half due to the nature of the weather conditions. South Africa also experiences alternating periods of droughts and floods which affects the amount of water across South Africa. In addition, hot dry conditions result in a high evaporation rate.
Rainfall (mm) for the season July 2011 to April 2012
Source: South African Weather Service
Frost, humidity and fog
Frost often occurs on the interior plateau during cold, clear, winter nights, with ice forming on still pools and in water pipes. The frost season (April to October) is longest over the eastern and southern plateau areas bordering on the escarpment. Frost decreases to the north, while the coast is virtually frost-free.
Average annual relative humidity readings show that, in general, the air is driest over the western interior and the plateau. Along the coast, the humidity is much higher, and at times may rise to 85%. Low stratus clouds and fog frequently occur over the cool west coast, particularly during summer. The “mist belt” along the eastern foothills of the escarpment is the only other area that commonly experiences fog.