The Olifants and Doring Rivers are the major drainage systems in the west, with the Gouritz River in the south-east of the biome. The Succulent Karoo Biome is primarily determined by the presence of low winter rainfall and extreme summer aridity. Rainfall varies between 20 and 290 mm per year. Because the rains are cyclonic, and not due to thunderstorms, the erosive power is far less than of the summer rainfall biomes. During summer, temperatures in excess of 40 C are common.
Fog is common nearer the coast.
Frost is infrequent. Desiccating, hot, Berg Winds may occur throughout the year. Grasses are rare, except in some sandy areas, and are of the C3 type. The number of plant species mostly succulents - is very high and unparalleled elsewhere in the world for an arid area of this size. Little data are available for the fauna of the Succulent Karoo.