Over the greater part of South Africa, most of the rain falls in the summer months (October to March, inclusive). If an irregular line be drawn from near East London in a westerly direc tion to near Laingsburg, then northward through Fraserburg, and curving north-westward to the coast, about 23° S., the area to the north and east of it is one that receives at least 6o% of its rain in summer. Part of it receives over 9o% of its total amount during these months. The south-west of the Cape Province is a region of winter rains. The area, lying to the west of another irregular line, drawn from about Bredasdorp, at first northward, and bending north-westward to meet the coast at 25° S., has 6o% or more of its rain in the winter months. Between these two areas is one where the rain is distributed fairly evenly throughout the year. At some places near the south coast, these rains may be appreciable in quantity, and here patches of forest occur.
In the summer rainfall area, much rain falls during thunder storms, the downpour often being very violent, causing much loss of water by run-off, and much soil erosion. Such storms are more characteristic of the inland districts. In the southern Kar roo five or six thunderstorms a year are recorded : at Johannes burg, 61. At the latter station lightning is seen on the average on 114 days every year. Precipitation during thunderstorms is often in the form of hail, which falls in the Transvaal on from 8o to 133 days in the year. Much damage is often done; crops may be entirely beaten down and ruined; small stock may be killed, and many roof tiles and windows broken. Snow falls principally in the mountains, especially along the great escarpment. Along the Basutoland section it may be seen even at midsummer. On Table Mountain (Cape Town) it falls about one year in six. In Natal it is rarely, if ever, seen below 4,000 feet.
South Africa is a land of intense sunlight, which is related to the clearness of the atmosphere, itself connected with high alti tudes and dryness. The average amount of bright sunlight re ceived each day throughout the year is 7.51 hours at Cape Town, 8.7 at Johannesburg, and 9.41 at Kimberley. With these fig ures may be compared the 3.8 hours for London. Evaporation is correspondingly high. The evaporation from a free water surface at Johannesburg is 74.67 inches per annum. This again diminishes the value of the rainfall to vegetation.
Owing to the small rainfall and high rate of run-off and evapora tion, South Africa is poorly supplied with forests. The country is covered with grasses, or, in the drier parts with low xerophytic shrubs and bushes. The grassland is best developed in the eastern half of the country. Three varieties of it are generally recognized: (I) The High Veld, which includes most of Basutoland, the Orange Free State, and the southern Transvaal, is a steppe re gion, with thorn trees growing on the rocky slopes. The domi nant grass is the red grass (Themeda triandra). Species of An dropogon, Panicum and Digitaria are also common. Herbaceous perennials are common. In the summer months the veld is in many places made beautiful by innumerable pink, white and mauve flowers of cosmos, which has spread among the indigenous flora. (2) The Eastern Mountain Grassland occurs along the slopes of the Stormberg and Drakensberg at altitudes of from 4,000 to 8,000 feet. The characteristic grasses are species of
Andropogon, Heteropogon, Panicum and Themeda. They all grow in tussocks and tufts. In this zone the bracken fern (Pteris aquilina) and composites are common. Tree ferns grow near the streams, and in some areas numerous, but scattered, protea bushes occur. (3) The Eastern Grass Veld is found over a strip of coun try extending between the great escarpment and the coast belt, from about Port Elizabeth northward through Natal, at heights ranging from i,000 to 4,000 feet. The broad monotony of the grassland is broken in places by low trees or bushes, which occur either individually or in small clumps. Among these are various species of thorn trees (Acacia spp., Zizyphus mueronata), the Cape lilac (Ehretia hottentotica). Aloes flourish on dry, rocky sites. On many slopes facing the north, the grassland is replaced, owing to intense insola_ion, dryness and exposure to hot winds, by an assemblage of thorn trees, aloes and euphorbias.
Desert or semi-desert associations cover much of the west and south: (I) Between the fold mountains of Cape Colony and the Escarpment, Karroo vegetation extends from the Olifants river, in the west, to about the Sundays river in the east. The rainfall is from 5 to i 5 in. per annum. The plants include succulents, such as Mesembryanthemum, Euphorbia, Aloes, Pelargonium, Sta pelia, etc. ; low shrubs, like the Karroo bush (Pentzia incana), and compositae. There are many bulbous and tuberous plants, which bloom for a short time after rains. Trees grow only along the dry river courses and on the mountain slopes in the east. (2) The upper Karroo comprises part of the interior plateau, south of the Orange river, and west of a line from Queenstown to Fauresmith, and the eastern part of Bushmanland. This, too, is a treeless area. The vegetation consists of small shrubs and low bushes. The most conspicuous of the succulent plants is Mesembryanthemum spinosum; aloes are common; grasses also occur, among the commonest being Aristida scabrivalvis, Era grostis truncata and E. obtusa. (3) Namaqualand : this botanical province includes part of Bushmanland, Little Namaqualand and most of Great Namaqualand above 2,000 feet. The rainfall is 5-10 inches. Tufted grasses grow on the higher plateaux and on sandy plains, but scattered, drought resisting shrubs and bushes, with succulents in the lower valleys and on rocky slopes are per haps more characteristic. (4) The Namib extends northward in a belt 18-35 m. wide along the west coast from Olifant's river. This area experiences the most arid conditions in South Africa, the rainfall being from 1 to 5 inches. On rocky hills grow species of Mesembryanthemum, Euphorbia virosa, Aloe dichotoma, etc. On the sand-dunes a few tufts of grass are to be f ound—Era grostes spinosa, E. cyperoides—together with Mesembryanthe mum Marlothi, and ganna bush (Salsola Zeyheri). Where under ground water can be reached the naras flourish (Acanthosicyos horrida) and the tamarisk (Tamarix articulata). The gravel Plains are the most barren of all. In places only an annual Me sembryanthemum occurs; in others only lichens. Welwitschia mirabilis is found in a few places. The characteristic plant is the Bushman's Candle (Sarcocaulon Burmanni).